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4 year old deck - snapped boards, flexing, cupping and badly dried out

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  1. #1
    Senior Member YoungBolt's Avatar
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    Default 4 year old deck - snapped boards, flexing, cupping and badly dried out

    Hi crew,

    I've got a bit of a rather expensive problem brewing with my, somewhat, recently build deck.
    I built my deck around 4 years ago and used 90x19mm greygum decking boards

    Last week I stepped on a board and it snapped under my foot into pieces. This was very surprising and unexpected. The next section of the same board also did the same.
    The board that snapped had some nasty white mushrooms of mould underneath it.
    The texture of the timber was chaulky. I have checked under the deck and found no evidence of termite damage or termites.

    This prompted me to start checking other boards and putting pressure on them. To my horror i'm finding many are flexing under my weight when I bounce on them. Many boards are cupping and dried out to buggery.

    The boards are meant to be greygum and were re-stained about 2 years ago with ultradeck acrylic stain.

    The deck is exposed 24/7 to the sun and rain, but I figured I would get a few more years out of them than just 4 years especially being greygum.

    The boards are spaced around 2mm apart. The lowest point of the deck is 250mm above the soil and the lowest point of the boards is 450mm so I wouldn't have thought it has any moisture issues. Highest part of the deck is 1m above the ground.

    One side of the deck is blocked up a retaining wall that has soil behind it and is level with the deck. The other side of the deck are fully open. The left side is hard up ahainst a brick wall and the right hand side is around 300mm from the fence.

    Like I said it is exposed to the sun and rain, but surely this isn;t the reason why the boards are degrading so quickly?

    The joists from what I can see are ok. They were painted and are 90x45 treated pine. I also put down some plascourse down to protect the top of the joists.

    What is causing this much damage?
    I will get some photos tonight to show the status of the boards.
    Attached Thumbnails Attached Thumbnails ca104f39-8d2f-412d-baee-7a3001f799f2.jpg   10b36b03-0d90-4766-b3e8-acf454ce5454.jpg   82ee064a-de9d-445d-960f-1f990aec4f76.jpg   e07d89e9-5a29-4eac-b733-dfd5b5e3feb8.jpg   b00b93d1-b412-40dc-bbd7-b79b6ccc7b74.jpg  

    ff45eab5-8386-418e-ab39-23c721a1ab87.jpg   03be74f2-af67-413e-84da-4ae352b27086.jpg   7a8f06a2-7f9d-425e-a1a5-94691a2b240e.jpg   41151747-5c20-4c1e-944e-e8f4d4349bf0.jpg   56ada35a-59a1-40f6-bc63-796b08d29b94.jpeg  


  2. #2
    Deactivated User Marc's Avatar
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    Poor quality timber on a low deck with little ventilation.

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    not sure if its greygum, but whatever it is it looks like feature grade to me. photo 3 looks like gum veins and knots to me - gum veins on horizontal exposed - not good

  4. #4
    Senior Member YoungBolt's Avatar
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    Quote Originally Posted by Marc View Post
    Poor quality timber on a low deck with little ventilation.
    3 things not going in my favour. Lucky me

    Is greygum considered poor quality? I'll be honest and say I got it for $2.80 L/M from a place called "Nationwide timber" who usually supplies timber windows and flooring.
    He sells these in bulk pack because he buys them from the same timber mill he gets the timber for his windows and floor. Is there differnet grades of decking boards? I figured greygum is greygum hardwood.

    Would treated pine have been better?

    Is 400mm off the ground considered low?! Isn't the moisture barrier 200mm?

    And last the ventilation part, what else can be done ?

    What are the usual standards/expectations of ventilation ? I figured having 2/4 sides open should be ok.

    Do I have to accept that this will keep happening because of bad design?

  5. #5
    Seasoned DIY droog's Avatar
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    I figured having 2/4 sides open should be ok.
    Ventilation requires air in and air out. If the two open sides are not opposite each other then you really have created a dead spot.
    Also looks like one open side is to the underside of the house, what is the ventilation under the house like ?

    Edit, sorry looks like one side is close to a fence so not much option for a breeze to flow in, might need assisted ventilation.

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    1K Club Member Gooner's Avatar
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    Those deck boards look like they haven’t seen a coat for more than 2 years. They don’t look very happy at all.

    I can’t quite make it out but it looks like the bearers are surrounded by some kind of flashing?

    I have a deck over 1m off the ground in the main area and I had a bunch of timber stored under there in a stack. I concreted under the deck and it has proper drainage. The timber was up off the ground on blocks. By the time I got around to using the timber, that white mould had gone through the bottom of the stack of timber like an alien forest and destroyed it.

    Mould needs a food source and moisture. The wood is the food source and it would seem you have a ventilation/moisture problem. Water & vinegar solutions may help kill white mould but you need to solve the moisture issue, it looks like the deck is surrounded by wall, fence, and timber. When it rains there probably isn’t, much ventilation under there to dry it out. Does water pool under there?

    id be looking at fixing that issue up one way or another. A roof over the deck may help but probably still need better ventilation. If the boards are flexing, I’d be replacing. No point sanding back and finishing if the timber is stuffed.
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    *If* it's Grey Gum, it should be fine for 40 years above ground

    https://www.woodsolutions.com.au/wood-species/gum-grey

    "Grey gum timber is extremely durable, with an in-ground life expectancy in excess of 25 years. For aboveground applications, life expectancy exceeds 40 years. Grey gum heartwood is termite-resistant, and untreated sapwood is not susceptible to lyctid borer attack.
    ...
    Grey gum is widely used in heavy engineering and marine construction, where it is found as poles, piles, railway sleepers, cross-arms and mining timbers. In general construction it is used for building framework, flooring and decking. Grey gum is also extensively used in landscaping and boat building."

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    Almost every thing you have done building this deck is contrary to the best advice on this forum.

    Low to ground with poor ventilation is probably the worst. Old experienced hands here get sick of trying to explain to the newcomer that building exposed, or really any timber deck, close to the ground is, at best, inadvisable.

    Poor quality of wood used... could throw in 'you get what you payed for" here, but I won't. It seems you aren't sure of even the type of timber. I doubt that rubbish in your photo's is Grey Gum. Reputable supplier comes to mind.

    A good quality coating applied when needed is essential, forget that acrylic water based rubbish, again the some of the old wizened hands here have changed there thinking over time. At the same time one must realize the most experienced builders here have to make a living and if his quote is higher than the opposition (because he has included a good quality oil coating in the price) he may loose the job, he must stay competitive. As a DIY home builder, that plans to stay put for a while, we should choose the best long term option.

    There's more but you must be getting the picture.

  9. #9
    Deactivated User Marc's Avatar
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    Oiling a deck prevents some cosmetic deterioration. Deck boards rot from below up, starting in butt joints and between joist and board under the deck. No oiling will ever prevent that.
    Fixing this deck will most likely include a lot of digging to improve ventilation, and re arrange the surroundings. not sure if it is feasible ,and hoping the frame is still sound.
    This from my armchair without the benefit of seeing the problem up close and personal.
    The deck boards are goners for sure. May be build a roof over it?

    Best of luck.

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    I've seen lower, with less ventilation, last 'decades' (in fact, I have one). This subfloor looks great, like the day it was built.

    Problem is elsewhere. E.g. Sold bad deck wood, or didn't get what you thought you were getting, and/or some infestation that 'the wrong wood' is susceptible to, etc etc

  11. #11
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    Those pics of the decking boards from top look like a 20 year old deck to me, not a 4 year old one.

    How often did you oil it, looks like it hasn't seen an oil since it was put down.
    Any Australian timber should last 20 years above ground with no maintenance, and double that with regular maintenance.

    It looks like white rot, which is caused by moisture trapped in the timber, the timber gets destroyed from within, so wouldn't surprise me if you find most of the timber has suffered the same fate.
    Mieux vaut prévenir que guérir

  12. #12
    Senior Member YoungBolt's Avatar
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    Firstly, thank you for the advice and feedback everyone - some are very helpful!

    Ultimately it looks like I've got a mixture of bad quality decking boards and potentially some ventilation issues as well.

    Neither of which are easy or cheap fixes. Fantastic.

    Quote Originally Posted by pharmaboy2 View Post
    not sure if its greygum, but whatever it is it looks like feature grade to me. photo 3 looks like gum veins and knots to me - gum veins on horizontal exposed - not good
    I think you might be right. I wasn't aware at the time the different gradings of decking. I just figured decking is decking.

    If you see the attached pictures, the original boards had heaps of inperfections such as knots, cracks, insect trails etc. I didn't think much of it at the time but these are the major areas where the timber has especially turned bad.

    Quote Originally Posted by Gooner View Post
    Those deck boards look like they haven’t seen a coat for more than 2 years. They don’t look very happy at all.

    I can’t quite make it out but it looks like the bearers are surrounded by some kind of flashing?

    I have a deck over 1m off the ground in the main area and I had a bunch of timber stored under there in a stack. I concreted under the deck and it has proper drainage. The timber was up off the ground on blocks. By the time I got around to using the timber, that white mould had gone through the bottom of the stack of timber like an alien forest and destroyed it.

    Mould needs a food source and moisture. The wood is the food source and it would seem you have a ventilation/moisture problem. Water & vinegar solutions may help kill white mould but you need to solve the moisture issue, it looks like the deck is surrounded by wall, fence, and timber. When it rains there probably isn’t, much ventilation under there to dry it out. Does water pool under there?

    id be looking at fixing that issue up one way or another. A roof over the deck may help but probably still need better ventilation. If the boards are flexing, I’d be replacing. No point sanding back and finishing if the timber is stuffed.
    I'm not 100% on when I stained them but I know I did at least once restain them. It has been a few years though and all the coating/stain is now coming up.

    The bearers dont have any flashing around them. There is a flashing between the joist and the bearer to try and protect the joints. I've also got some plascourse flashing between the deck boards and the deck joists as well. Stumps obvious have some ant caps.

    Interesting situation you have considering you actually did concrete it too. Looks like mould can really eat up boards quickly, even if they are hardwood.

    A roof over the deck would be quite complicated, expensive and the area is small so I have concerns it'll make the area feel quite closed in and tight.
    The deck was originally just meant to be a nice area to sit down on because there was no outside entertaining area. I did want the deck as a bit of a feature but it's turned into one for all the wrong reasons!

    Looks like you're right about the boards look like they've had their time and experienced an incredible amount of wear in a short time. It's just depressing to seem them so degraded. It took a few weekends of cashies to save up for them too.


    Quote Originally Posted by r3nov8or View Post
    *If* it's Grey Gum, it should be fine for 40 years above ground

    https://www.woodsolutions.com.au/wood-species/gum-grey

    "Grey gum timber is extremely durable, with an in-ground life expectancy in excess of 25 years. For aboveground applications, life expectancy exceeds 40 years. Grey gum heartwood is termite-resistant, and untreated sapwood is not susceptible to lyctid borer attack.
    ...
    Grey gum is widely used in heavy engineering and marine construction, where it is found as poles, piles, railway sleepers, cross-arms and mining timbers. In general construction it is used for building framework, flooring and decking. Grey gum is also extensively used in landscaping and boat building."
    By all accounts the retailer did say it was greygum. I believe he said it came from southern NSW. I remember them being incredibly tough to drill and the stainless screws could break if you didn't countersink the holes in the board enough. Maybe these were some nasty seconds or something.

  13. #13
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    Quote Originally Posted by METRIX View Post
    Those pics of the decking boards from top look like a 20 year old deck to me, not a 4 year old one.
    I had that same thought.

    If I was to do that again I would ensure the subframe is resilient to decay, replace decking with knotless treated pine, solid paint before grain opens up. But critically the 2mm gap is ridiculous for that environment and I would have it as large as you can accept, maybe 8mm.

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    Quote Originally Posted by Bushy View Post
    Almost every thing you have done building this deck is contrary to the best advice on this forum.

    Low to ground with poor ventilation is probably the worst. Old experienced hands here get sick of trying to explain to the newcomer that building exposed, or really any timber deck, close to the ground is, at best, inadvisable.

    Poor quality of wood used... could throw in 'you get what you payed for" here, but I won't. It seems you aren't sure of even the type of timber. I doubt that rubbish in your photo's is Grey Gum. Reputable supplier comes to mind.

    A good quality coating applied when needed is essential, forget that acrylic water based rubbish, again the some of the old wizened hands here have changed there thinking over time. At the same time one must realize the most experienced builders here have to make a living and if his quote is higher than the opposition (because he has included a good quality oil coating in the price) he may loose the job, he must stay competitive. As a DIY home builder, that plans to stay put for a while, we should choose the best long term option.

    There's more but you must be getting the picture.
    ok.

    The lowest point of the deck is 400mm off the ground. By all accounts that is beyond the minimum recommendation for a deck I've seen. The lowest point is 400mm, but the majority is higher than that and the end of it is 1000mm off the ground.

    I wasn't aware that the ventilation is bad. I installed bigger gaps between the boards than normal (2mm gaps) and there's still about a foot of gap between the deck and the fence on one side, it's completely open on one other side and there is a small gap between the deck and the retaining wall. The only "sealed" side is the house side, but I left old manhole was open to allow for some air flow from under the house to go through the area as well.

    I agree that the timber is probably some cheap quality stuff. I figured at the time it was much cheaper than retail because the supplier was not a traditional timber supplier with overheads. This was someone who basically bulk buys timber and resells it to either retailers or direct to public. 4-5 years down the road I can see this is obviously incorrect.

    Quote Originally Posted by Marc View Post
    Oiling a deck prevents some cosmetic deterioration. Deck boards rot from below up, starting in butt joints and between joist and board under the deck. No oiling will ever prevent that.
    Fixing this deck will most likely include a lot of digging to improve ventilation, and re arrange the surroundings. not sure if it is feasible ,and hoping the frame is still sound.
    This from my armchair without the benefit of seeing the problem up close and personal.
    The deck boards are goners for sure. May be build a roof over it?

    Best of luck.
    Thank you. Interesting. I figured there must be more of an issue than just a deck not oiled enough or with the wrong products.

    If was to try and save it from any further deterioration or improve the ventilation for the next set of boards, what would I need to do to improve the ventilation?
    If increase the gap between the deck and the fence, then it becomes mostly unusable as a space. The max distance fro mthe house to the end of the deck is 4m at it's widest and 2m at it's thinnest.
    The retaining wall at the top part of the courtyard is basically level with the back gate entry to the courtyard.

    I did a stackload of work to this yard to try and improve drainage and make it usable space. It used to just be all paved on a huge slant and all the water used to rush down the property into the garage and shed at the bottom. I cut up the 3 sections with the 1st section being a flat area with a retaining wall, and flowing onto the 2nd section where I had this deck. The deck then leads onto 3rd section was which was dug down to create a base for the shed level with the entry to the garage.

    Frame for the deck looks go far. I've crawled udner there and tapped it down a hammer and can't hear any tinny noises or find any signs of rot/damage.

    Quote Originally Posted by r3nov8or View Post
    I've seen lower, with less ventilation, last 'decades' (in fact, I have one). This subfloor looks great, like the day it was built.

    Problem is elsewhere. E.g. Sold bad deck wood, or didn't get what you thought you were getting, and/or some infestation that 'the wrong wood' is susceptible to, etc etc
    So it could purely be the deck boards? Frustrating situation if it is, but it at least would mean I wouldn't need to completely redesign my little courtyard or do major work. I've spent ages as it is on this tiny crappy courtyard.

    I am up for a good $1.2-1.5k for new deck boards. I'd hate to fork out that money for it to only rot out like this again.

    Is there any ways to test the ventilation or moisture undearnath? In all honesty the soil has and is almost always moist or wet. It's very rarely dry under there.

    If I was to replace the deck boards, would it be worth covering the base in crushed rock or similar to help with water dispersion.

    The other option is to just remove the entire deck and pave the area instead. Not the easiest option nor a favored option as I would have to rip out many weekends of work and prep I did to level this yard and make it somewhat usable for it's size.
    I would also need to do some more work to the 1st retaining wall to try and make this area level.

  15. #15
    Community Moderator phild01's Avatar
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    When I have done a low deck with possible moisture issues, I lay weed mat and overlay it with something like road base. The weed mat lets water down but inhibits it from rising.

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    Quote Originally Posted by YoungBolt View Post
    Hi crew,

    I've got a bit of a rather expensive problem brewing with my, somewhat, recently build deck.
    I built my deck around 4 years ago and used 90x19mm greygum decking boards

    Last week I stepped on a board and it snapped under my foot into pieces. This was very surprising and unexpected. The next section of the same board also did the same.
    The board that snapped had some nasty white mushrooms of mould underneath it.
    The texture of the timber was chaulky. I have checked under the deck and found no evidence of termite damage or termites.

    This prompted me to start checking other boards and putting pressure on them. To my horror i'm finding many are flexing under my weight when I bounce on them. Many boards are cupping and dried out to buggery.

    The boards are meant to be greygum and were re-stained about 2 years ago with ultradeck acrylic stain.

    The deck is exposed 24/7 to the sun and rain, but I figured I would get a few more years out of them than just 4 years especially being greygum.

    The boards are spaced around 2mm apart. The lowest point of the deck is 250mm above the soil and the lowest point of the boards is 450mm so I wouldn't have thought it has any moisture issues. Highest part of the deck is 1m above the ground.

    One side of the deck is blocked up a retaining wall that has soil behind it and is level with the deck. The other side of the deck are fully open. The left side is hard up ahainst a brick wall and the right hand side is around 300mm from the fence.

    Like I said it is exposed to the sun and rain, but surely this isn;t the reason why the boards are degrading so quickly?

    The joists from what I can see are ok. They were painted and are 90x45 treated pine. I also put down some plascourse down to protect the top of the joists.

    What is causing this much damage?
    I will get some photos tonight to show the status of the boards.
    I'd say the board that broke was all sapwood, grey gum sapwood deteriorates very quickly, it should have been graded out or pressure treated, it is really easy to pick , sapwood is pale white to yellowish, whereas the true wood is deep red/brown, one of the hardest of the hardwoods , easily up there with ironbark.
    inter

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    Quote Originally Posted by METRIX View Post
    Those pics of the decking boards from top look like a 20 year old deck to me, not a 4 year old one.

    How often did you oil it, looks like it hasn't seen an oil since it was put down.
    Any Australian timber should last 20 years above ground with no maintenance, and double that with regular maintenance.

    It looks like white rot, which is caused by moisture trapped in the timber, the timber gets destroyed from within, so wouldn't surprise me if you find most of the timber has suffered the same fate.
    They're around 4-5 years old. From memory I built it in late 2016 / early 2017. It has been restained once, but I've been caught up with other projects and work so haven't attended to it for some years.

    I just kept putting it in the "i'll do it next weekend" basket until last weekend when I unexpectedly managed to make contact with the soil underneath.

    So if it was white rot, then it's something to do with the original timber? Is the environment that caused it, or a dodgy batch of timber I bought?

    What other telltale signs of white rot is there?


    Quote Originally Posted by phild01 View Post
    I had that same thought.

    If I was to do that again I would ensure the subframe is resilient to decay, replace decking with knotless treated pine, solid paint before grain opens up. But critically the 2mm gap is ridiculous for that environment and I would have it as large as you can accept, maybe 8mm.
    What could I do to make the subframe more resilient to decay? I painted all of the joists and bearers with two coats of paint rated for external use.

    I'm happy to use treated pine and paint it if that is a better option.

    I didn't realise the area was so bad for a deck to survive long term. If I do install new deck boards at wider gaps then I'm going to need to install new joists due to all the existing holes in it no?

    .
    Would it be a better idea to rip out the deck and install a paved area instead?

  18. #18
    Senior Member YoungBolt's Avatar
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    Here’s some photos of the deck post install, and some of the space around it
    Attached Thumbnails Attached Thumbnails 930a16e0-4209-45a5-a147-753b67d8cde4.jpg   883994f1-cb6d-4636-8a02-3b8da5223b29.jpg   bf1eb80e-dfb6-4142-a580-cdaae45b0429.jpg   ac3b3fc9-a0a7-4f9b-9c03-adcbb2bdcf1e.jpg   6526ff30-00ff-4861-a2a5-02dad61d3add.jpg  


  19. #19
    Deactivated User Marc's Avatar
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    One critical aspect of ventilating a low deck is the gap between boards, not how far the fence is from the edge. lacking hight and opening to the wind to flow, the gaps between boards play a critical role.
    2 mm gets plugged up quickly with debris, and airflow becomes zero.

    I suggest that once you lift the old boards, and remove all screws, you assess how much soil is it possible to remove safely and without creating a pool for water to sit. How much can airflow be improved by opening up one or more sides.
    Proceed to give the frame two coats of exterior water based paint and install "protectadeck" on bearers and joist.
    Choose a good quality species of hardwood. In victoria you have Demak, a supplier that is a member on this forum and sells good stuff.

    If it is me, and after this experience, I would, first of all, stack the boards under cover and sticker them for a month. Then give it a coat of oil based primer and two coats of solid water based exterior paint all around before installing.
    Others may think this is a heresy and that deck should be oiled. Up to you.

    When installing, keep the gap at 5mm not less. use one of the jigs for this purpose, like deckhand https://www.betterhardware.com.au/de...late-tool.html Remember that this gaps are the important one. The biger the better within reason ... that is ... no so big that you can step in them

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    Quote Originally Posted by YoungBolt View Post
    ....
    I didn't realise the area was so bad for a deck to survive long term. If I do install new deck boards at wider gaps then I'm going to need to install new joists due to all the existing holes in it no?
    ...
    The site itself is really not that bad.

    Don't replace the joists. Replace the protective plastic

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    Quote Originally Posted by r3nov8or View Post
    The site itself is really not that bad.
    What makes it bad is how enclosed it is, ventilation is key and the deck boards need to breathe with wide spacings.

    I have found treated pine is the better choice in damp areas. Also far favour a solid painted deck to any other type of wood finish, they just go on looking good longterm provided it is done before the grain opens up and is re-coated every few years as opposed to stripping and re-coats every 6-12 months.

    Many exposed decks are neglected in the first few years and end up looking like rubbish if deprived of the never ending maintenance routine. Cabots decking paint is an excellent product.

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    Quote Originally Posted by phild01 View Post
    ...
    Many exposed decks are neglected in the first few years and end up looking like rubbish if deprived of the never ending maintenance routine. Cabots decking paint is an excellent product.
    Of course, there is Modwood, which I've said before, done right, to the letter, is, in my experience, just great

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    Quote Originally Posted by r3nov8or View Post
    Of course, there is Modwood, which I've said before, done right, to the letter, is, in my experience, just great
    Just revisited the Trex deck I did and it looks just the same as day one. Agree with a good quality composite deck.

  24. #24
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    Quote Originally Posted by YoungBolt View Post
    They're around 4-5 years old. From memory I built it in late 2016 / early 2017. It has been restained once, but I've been caught up with other projects and work so haven't attended to it for some years.

    I just kept putting it in the "i'll do it next weekend" basket until last weekend when I unexpectedly managed to make contact with the soil underneath.

    So if it was white rot, then it's something to do with the original timber? Is the environment that caused it, or a dodgy batch of timber I bought?

    What other telltale signs of white rot is there?




    What could I do to make the subframe more resilient to decay? I painted all of the joists and bearers with two coats of paint rated for external use.

    I'm happy to use treated pine and paint it if that is a better option.

    I didn't realise the area was so bad for a deck to survive long term. If I do install new deck boards at wider gaps then I'm going to need to install new joists due to all the existing holes in it no?

    .
    Would it be a better idea to rip out the deck and install a paved area instead?
    White Rot or Wet Rot can easily be identified by the white / brownish mould on the timbers underneath, your picture looks to be pretty much what's caused the problem, it attacks the internal timber structure eventually weakening it from within.

    I would say it's a combination of a moisture problem under the deck, lack of airflow and poor quality timber that was more prone to it due to it's lower grade.
    The timber you sourced was fine for screening and feature wall or an exposed deck with really good cross ventilation under it, or a covered deck, as long as it was oiled on a regular basis.

    Your deck doesn't look that bad underneath for clearance, if you say the lowest point is 400 and highest is 1000 that's fine, I have seen many lower decks still going after 20 years.
    The problem looks to be moisture build up under there with no crossflow ventilation to effectively dry it out.

    You need to do something to get more ventilation under there, get rid of any stuff you store under there, what is that pine retaining wall you built at one end, this will completely stop any airflow getting under there.

    You would be better off replacing the boards with H3 TP, the treatment will help with the mould getting a hold onto the boards, I would also coat the bottoms of the boards with either an oil based undercoat or waterproofing compound.
    The idea is to keep moisture in your case probably condensation, from sitting on the raw timber, if you say the H3 joist / bearer are in perfect condition this will give you an indication of what works.

    Most importantly with pine is to keep the boards either sealed with paint on top and sides or oil them regularly, looking at the current tops of the boards you have completely ignored any maintenance on them, you can't do that. a deck needs constant maintenance.

    I always tell my clients if they don't want to do the maintenance either because they don't have the time or are not interested, then don't install a deck, or pay someone to do the regular yearly clean / oil for them because they are just throwing money away as the deck wont look good or last, or put a roof over it to protect it is the best option.

    As for the joists already screwed, if you do go for new boards replace the damp course with protect deck, this will cover the existing screw holes and stop water getting into them, the beauty of protect deck is any fixings that penetrate it the rubber self heals around the penetration effectively keeping water out.

    Gaps for boards should be 3-4mm for hardwood as the timber will slightly shrink in the first 12 months giving you around a 5mm gap, TP needs to be around 5-6mm, it will shrink and expand constantly.

    Tell-tale sigs of your problem shown below, there is plenty of information out there on what causes it, it all comes down to two things, dampness and lack of airflow, if your boards were grey gum and they disintegrated in 4 years you must have a severe damp / lack of airflow problem.

    Your pic and others, they look very similar.
    7a8f06a2-7f9d-425e-a1a5-94691a2b240e.jpg


    995020497-1.jpg

    0220-sr-2.jpg
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    Thanks again everyone for your time and help with this. Very much appreciated!

    Quote Originally Posted by Marc View Post
    One critical aspect of ventilating a low deck is the gap between boards, not how far the fence is from the edge. lacking hight and opening to the wind to flow, the gaps between boards play a critical role.
    2 mm gets plugged up quickly with debris, and airflow becomes zero.

    I suggest that once you lift the old boards, and remove all screws, you assess how much soil is it possible to remove safely and without creating a pool for water to sit. How much can airflow be improved by opening up one or more sides.
    Proceed to give the frame two coats of exterior water based paint and install "protectadeck" on bearers and joist.
    Choose a good quality species of hardwood. In victoria you have Demak, a supplier that is a member on this forum and sells good stuff.

    If it is me, and after this experience, I would, first of all, stack the boards under cover and sticker them for a month. Then give it a coat of oil based primer and two coats of solid water based exterior paint all around before installing.
    Others may think this is a heresy and that deck should be oiled. Up to you.

    When installing, keep the gap at 5mm not less. use one of the jigs for this purpose, like deckhand https://www.betterhardware.com.au/de...late-tool.html Remember that this gaps are the important one. The biger the better within reason ... that is ... no so big that you can step in them
    Ok, interesting!

    I remember installing it with 3mm gap, but over time with the hardening of the timber, it's reduced to 2mm. Debris very easily gets stuck in the gaps and i'm forever picking it out.

    As far as opening up the sides, I dont really have an option with the current setup unfortunately. There's a retaining wall at the opening that is right up against the deck. The courtyard is on a huge slant and so I created a little flat area before the deck to level out the yard. The idea was that you'd have a small grassy area from the back gate to the deck and then walk straight onto the deck. I wasn't so keen for a deck per se, but to try and level out the yard, make it somewhat useful wth an entertaining area and also stop the river that used to flow down the courtyard and into the garage at the bottom of the property.

    I can remove some dirt underneath, but what would that do for airflow? The more I remove, the less footing the deck stumps have as well.
    I was thinking of putting down some weedmat and crushed rock ontop to help with water dispersion.

    The frame has two coats of exterior rated paint, but happy to throw anouther lick on it.

    I'll definitely invest into protectadeck. I think my cheap plascourse isn't likely doing enough compared to the rubber protectadeck you can buy.

    If I do replace the boards, I'll definitely increase the gaps to at least 5mm, maybe go more, and as you say let them dry out a bit before. It will need to be well oiled or painted I think.

    Quote Originally Posted by phild01 View Post
    What makes it bad is how enclosed it is, ventilation is key and the deck boards need to breathe with wide spacings.

    I have found treated pine is the better choice in damp areas. Also far favour a solid painted deck to any other type of wood finish, they just go on looking good longterm provided it is done before the grain opens up and is re-coated every few years as opposed to stripping and re-coats every 6-12 months.

    Many exposed decks are neglected in the first few years and end up looking like rubbish if deprived of the never ending maintenance routine. Cabots decking paint is an excellent product.
    Yep, makes sense.

    I can't do much to increase the ventilation from the sides.

    How do you assess when an area is damp and could have issues prior to a deck install? Prior to the deck there was pavers and the area was quite dry. I'm surprised at how there it is so damp under the deck.

    If I do keep the current setup, I will likely switch to TP and paint it well. I figured a hardwood would be more weather resistant and hold up better longterm than TP, but I underestimated how much ventilation I need, the moisture build up underneath and maintenance it needs. Sounds like painted TP would be a better choice for the area.

    If regularly painted and maintained, would the TP boards be able to last 10+ years?

    Quote Originally Posted by METRIX View Post
    White Rot or Wet Rot can easily be identified by the white / brownish mould on the timbers underneath, your picture looks to be pretty much what's caused the problem, it attacks the internal timber structure eventually weakening it from within.

    I would say it's a combination of a moisture problem under the deck, lack of airflow and poor quality timber that was more prone to it due to it's lower grade.
    The timber you sourced was fine for screening and feature wall or an exposed deck with really good cross ventilation under it, or a covered deck, as long as it was oiled on a regular basis.

    Your deck doesn't look that bad underneath for clearance, if you say the lowest point is 400 and highest is 1000 that's fine, I have seen many lower decks still going after 20 years.
    The problem looks to be moisture build up under there with no crossflow ventilation to effectively dry it out.

    You need to do something to get more ventilation under there, get rid of any stuff you store under there, what is that pine retaining wall you built at one end, this will completely stop any airflow getting under there.

    You would be better off replacing the boards with H3 TP, the treatment will help with the mould getting a hold onto the boards, I would also coat the bottoms of the boards with either an oil based undercoat or waterproofing compound.
    The idea is to keep moisture in your case probably condensation, from sitting on the raw timber, if you say the H3 joist / bearer are in perfect condition this will give you an indication of what works.

    Most importantly with pine is to keep the boards either sealed with paint on top and sides or oil them regularly, looking at the current tops of the boards you have completely ignored any maintenance on them, you can't do that. a deck needs constant maintenance.

    I always tell my clients if they don't want to do the maintenance either because they don't have the time or are not interested, then don't install a deck, or pay someone to do the regular yearly clean / oil for them because they are just throwing money away as the deck wont look good or last, or put a roof over it to protect it is the best option.

    As for the joists already screwed, if you do go for new boards replace the damp course with protect deck, this will cover the existing screw holes and stop water getting into them, the beauty of protect deck is any fixings that penetrate it the rubber self heals around the penetration effectively keeping water out.

    Gaps for boards should be 3-4mm for hardwood as the timber will slightly shrink in the first 12 months giving you around a 5mm gap, TP needs to be around 5-6mm, it will shrink and expand constantly.

    Tell-tale sigs of your problem shown below, there is plenty of information out there on what causes it, it all comes down to two things, dampness and lack of airflow, if your boards were grey gum and they disintegrated in 4 years you must have a severe damp / lack of airflow problem.

    Your pic and others, they look very similar.
    wow judging by those pictures - I've very likely got white rot issues. It hasn't seem to rear it's ugly head on all the boards, but there are a noticeable few more with the telltale signs. Might just be a matter of time until they're all stuffed.

    Does white rot form or is it embedded in the timber before I laid it?

    I can see now that the lack of airflow and moisture build up underneath wouldn't hve helped the situation. Would I have ended up here if it was regularly maintained?

    I wasn't aware of the grade of decking board. Just trusted the seller that it's good quality. Old mate has done a number on me.

    I will go for TP boards as a replacement. They are at least cheaper than hardwood and by a few accounts seems are more resilient to moisture and rot issues. I'll definitely paint the undersides as well.

    With regards to the retaining wall, I installed that to create a level area toward the back of the courtyard. It was on a big slant and there was no flat area in the entire yard. I didn't think that the retaining wall would cause much problems. There's not a whole lot I can do about it now though, unless I remove the entire back section there and reinstall the big sloping area that effectively becomes useless.

    AS you say I've done minimal maintenance on the boards. Got held up with lots of projects and work so it fell into the "next weekend" basket that didn't eventuate much.

    I think my biggest problem is likely lack of ventilation so any condensation or rain that comes through the boards can't dry out effectively. I'll go around underneath and stab the joists & bearers with a screwdriver, but visually I couldn't see any rot issues.

    ----

    With all the discussion around the poor airflow and moisture issues, is it worth ripping out the deck and paving the area instead?

    Replacing boards is going to be anywhere from $1500-$2500. I have an area of approx 18 sqm of area to cover so even at the average price of $3.50/lm I'm up for $1000 alone for the boards, plus I need to likely will need to also buy new screws again which are around $200 as I doubt the existing ones will come out nice and straight or without busted heads, plus a good few rolls of $50/roll protectadeck and then the costs for paint and/or oil.

    If I'm going to fork the money out and likely be back here in a handful of years then I may as well just pave it all and pull out the deck. I do plan to sell/rent out this place in the next 1-2 years as I would like to upgrade but because I dont know if I will be able to rent it out and hve to sell, I want to be able to try and do things to last a bit of time incase i'm wearing the expenses for any damage tenants might cause

    I will post up some pictures of the yard and see what solutions we can come up with for the yard?

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    Does that area get good direct sunlight, if it is cold and little sunlight then decay can set in. I know with spotted gum that the dampness issue would not necessarily be as bad as yours. One deck recently I looked at, spotted gum and the 90x19 boards were terribly cupped after a couple of years since new. When the boards were lifted they were completely wet underneath but no decay. The gaps were about 3mm too. That deck got good direct sunlight though and about 600mm above wet ground.

    If you do use treated pine I would be hesitant to fully encase them in paint. You have not noted any dampness under the existing boards so the type of timber you have used might be the major contributing factor as well. I once built a deck using cheap hardwood and it was rubbish after a few years, it has been redone in treated pine with 5mm gaps,solid Cabots paint, is closer to the ground than yours but with good ventilation. It is still in perfect condition after say 10 years. The underside was not painted.
    Attached Thumbnails Attached Thumbnails tp-deck.jpg  

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    When I redid that deck, because the joists were saturated with nail holes, I flipped the joists over, being TP they were still serviceable.

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    Funnily enough it gets heaps of sunlight.

    The board that broke still felt a little damp underneath. I've felt the ones closest to the opening and they are fairly damp underneath and it hasn't rained here in about 2 days or so.

    Impressive outcome Phil with that deck!

    My joists were held on with twisties so I dont think it would be very salvageable once I rip those out.

    I'm still considering just ripping out the deck and paving the area.
    It'd be a bit depressing considering there's approx $1000 worth of sub-frame materials going to waste, and I'd need to do a bit of extra work to remove and reinstalling a higher retailing wall lower down the yard.
    Plus you'd have at least 3-4 steps coming out from the house to step onto the paved area.

    I've taken a few crappy photo's of the yard to give some idea of what i'm dealing with. Excuse all the rubbish and junk. I'm still renovating some things and there's plenty of left over junk. And I need to get out the brushcutter to attack all the random grass!
    Attached Thumbnails Attached Thumbnails 86cd824b-92c6-46be-a329-bdd14b0ef1b1.jpg   abcc1e58-524f-40bf-a3cc-0f4a67fd7a31.jpg   e4ea50c9-eba1-4420-9332-9fc21e0b5b65.jpg   43457ec4-c3d5-4c21-8bbf-30c572360ee5.jpg   5c2ee965-65e1-4fe3-9d98-a937113c424b.jpg  

    d6ffdd0d-166b-494b-af5b-42d9dfda3de9.jpg  

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    Can you use a 5 to 6mm gap over most of the deck and open up the spacing towards the fence side?
    Anything greater than 12mm becomes trip hazard with high heels tho I guess, neither Cecile or I wear stiletto heels .
    I used 5mm but opened up a few to 8mm so I didn't have to buy another length of decking and 8mm causes no issues and still looks OK with 80mm boards
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    I would be using the joist and bears as an indication of what to use and do.

    I looks like you painted them all the way around, if you pull up the boards and the tp is still fine then there's the answer, I suspect the boards you got appear to be of lower grade.

    This guy probably buys them from auctions in bulk that are only fit for undercover decks or screens then sells them as higher grade timber at a cheaper price, punters will buy them thinking they are getting a bargain.

    I have seen decking boards at auctions that were only fit for firewood.

    And no wet rot is not part of the timber it is attracted to timbers that are damp and not ventilated, it everywhere just waiting for the right situation.
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    Quote Originally Posted by Moondog55 View Post
    Can you use a 5 to 6mm gap over most of the deck and open up the spacing towards the fence side?
    Anything greater than 12mm becomes trip hazard with high heels tho I guess, neither Cecile or I wear stiletto heels .
    I used 5mm but opened up a few to 8mm so I didn't have to buy another length of decking and 8mm causes no issues and still looks OK with 80mm boards
    If I replace the boards, I will be switching to bigger gaps. I think I'll go with 6mm gap as a minimum. I'll try 8mm first and see how wide it is. No one in this house wears stillettos either so pretty safe there....well at least my misso's doesn't, as for me..if the money's right or i'm desperate


    Quote Originally Posted by METRIX View Post
    I would be using the joist and bears as an indication of what to use and do.

    I looks like you painted them all the way around, if you pull up the boards and the tp is still fine then there's the answer, I suspect the boards you got appear to be of lower grade.

    This guy probably buys them from auctions in bulk that are only fit for undercover decks or screens then sells them as higher grade timber at a cheaper price, punters will buy them thinking they are getting a bargain.

    I have seen decking boards at auctions that were only fit for firewood.

    And no wet rot is not part of the timber it is attracted to timbers that are damp and not ventilated, it everywhere just waiting for the right situation.
    As far as I can tell the TP joists & bearers are fine. There's a few areas where I didn't paint and the cuts/exposed sections still look brand new. No rot to be seen.

    Likely is to do with having cheap boards, less than ideal ventilation and lack of maintenance on my part.

    I wont be buying anything from that guy again. Dodgy AF.


    If I replace the boards with TP and paint the top & sides of them, how long can i expect them to last? I will commit to repainting them at least once a year.

    Is it worth ripping out the deck and installing paving instead?

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    With paving won't you want the area to be level, could be problematic with any subsidence.

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    All the suggestions so far are like cracking an egg with a sledgehammer, your decking boards were substandard & more than likely not even grey gum, Grey gum without sapwood could be laid straight on the ground in the dirt & it wouldn’t rot in 20 years.
    Inter

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    Personally I wouldn't be ripping it out and putting down paving. I think the deck is a much better feature to have than paving. I wouldn't even consider it personally.

    You say you will need to buy new screws but probably won't. I have had to remove plenty of screws from my deck (had to replace a 6m rotted joist once and that one time when a piece of burning timber fell from the fire pit and put the deck on fire....) and the screws all came out fine. Stainless screws into merbau and hardwood joists. I've had issues with my deck, but nothing that couldn't be fixed.

    Looks like you will need to rip out the boards but perhaps you can use them down the track for screening or something else. That's what I did with my pergola. Old deck boards came up a treat when used for screening on the pergola even though they looked stuffed (similar to yours) when I pulled them out. (They were part of that stack of wood that the white rot had gotten to I mentioned in a previous post.)

    You may opt to spend a little extra and put down the composite deck boards. You mention you may want to rent out the place. If you do that, your renters are not going to be maintaining the deck and you probably won't want to be going there every so often to maintain it either. So using something like Ekodeck may be a good option.

    As others have said, wider spacing between boards, improve ventilation and drainage (perhaps grade the soil to one side, plastic sheeting/weed mat and crushed rock on top) and perhaps consider putting a simple roof over the deck. Perhaps a waterproof shade sail to partially cover the deck and give you some shade at the same time.

    The frame all looks good. Concrete stumps, ant caps, painted frame, etc. I wouldn't be giving up on this deck just yet.
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    Here you go...

    https://www.atfa.com.au/wp-content/uploads/2017/11/79_Deck_Ventilation.pdf

    I think you will relate to this. Deck rotting in 4 years.

    Also mention about plastic sheet with gravel on top.

    Don't give up.
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    Re the paving concept and considering keeping the flow from the house level, you could consider laying a cement sheet floor and tiling it. (Others might be able to recommend the specifics )

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    Quote Originally Posted by Gooner View Post

    Also mention about plastic sheet with gravel on top.
    Gee, great to know an idea I came up with and use is also documented. Personally I think weed mat is better because water can escape into the soil and not pool on the membrane.

  38. #38
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    Thanks for the continual assistance with this dilemma!

    Quote Originally Posted by intertd6 View Post
    All the suggestions so far are like cracking an egg with a sledgehammer, your decking boards were substandard & more than likely not even grey gum, Grey gum without sapwood could be laid straight on the ground in the dirt & it wouldn’t rot in 20 years.
    Inter
    What do you mean by your analogy?

    I agree that the boards are like some nasty seconds or cheap quality. The retailer was not a decking or timber retailer direct to public, but more someone who buys bulk packs of timber and onsells them to other retailers or producers of windows, door frames, flooring etc

    I've learnt the hardway now, but will hopefully make changes that will ensure it wont happen again.

    Quote Originally Posted by Gooner View Post
    Personally I wouldn't be ripping it out and putting down paving. I think the deck is a much better feature to have than paving. I wouldn't even consider it personally.

    You say you will need to buy new screws but probably won't. I have had to remove plenty of screws from my deck (had to replace a 6m rotted joist once and that one time when a piece of burning timber fell from the fire pit and put the deck on fire....) and the screws all came out fine. Stainless screws into merbau and hardwood joists. I've had issues with my deck, but nothing that couldn't be fixed.

    Looks like you will need to rip out the boards but perhaps you can use them down the track for screening or something else. That's what I did with my pergola. Old deck boards came up a treat when used for screening on the pergola even though they looked stuffed (similar to yours) when I pulled them out. (They were part of that stack of wood that the white rot had gotten to I mentioned in a previous post.)

    You may opt to spend a little extra and put down the composite deck boards. You mention you may want to rent out the place. If you do that, your renters are not going to be maintaining the deck and you probably won't want to be going there every so often to maintain it either. So using something like Ekodeck may be a good option.

    As others have said, wider spacing between boards, improve ventilation and drainage (perhaps grade the soil to one side, plastic sheeting/weed mat and crushed rock on top) and perhaps consider putting a simple roof over the deck. Perhaps a waterproof shade sail to partially cover the deck and give you some shade at the same time.

    The frame all looks good. Concrete stumps, ant caps, painted frame, etc. I wouldn't be giving up on this deck just yet.

    Quote Originally Posted by Gooner View Post
    Here you go...

    https://www.atfa.com.au/wp-content/uploads/2017/11/79_Deck_Ventilation.pdf

    I think you will relate to this. Deck rotting in 4 years.

    Also mention about plastic sheet with gravel on top.

    Don't give up.
    wow yes that pretty much looks like my deck boards. Who have thought that low ventilation and crappy boards could look so terrible in such a small amount of time.

    If I can reinstall some decking boards that will last for a good 10+ years then I'd prefer that then ripping up the deck. The sub-frame looks to have survived well so it'd be a shame to pull it out. Plus I do like being able to walk out of the house straight onto the deck - the house is small 2bd unit so the outside deck area from the kitchen & dining room makes it feel a little bigger.

    I've spent long enough of this tiny house in the last 2-3 years. I'm wanting to have a my weekends back so a quick, and relatively cheap fix is preferable.
    Ripping up the deck would suck and then I'd be up for a good stack of weekends to remove the lower retaining wall and reinstall a higher one, level the old deck area, pack it down, put sand down, pave it all and install stairs for the external doors.

    I didn't think of reusing the deck boards but I've got a thicknesser so I can least make them flat again and use for screening or for a balustrade screen.

    Looking at the cost for ecodeck and the low amount of time they've been in the market, I might just stick with TP for now.

    Is it possible to stain and oil TP To look similar colour to merbau and still last? Or I should just paint it and dont leave it unpainted?

    With regards to the floor, there should already be some flow as the ground slopes downwards to the front retaining wall near the shed. There's an approx 500mm elevation across 6m which means it has a 5 deg incline.
    At the end of the deck I've installed a retaining wall with agi pipe behind it and it's all been backfilled with scoria and crushed rock. Does it need more of a slope for good drainage?

    Should I maybe try and slope the floor toward the fence side and install an agi pipe or drainage channel?

    I'll definitely go with the suggestions for wider spacing between boards (probably 6mm), install protectadeck, put down weed matt and/or plastic sheet with a stackload of rocks ontop.
    Going to be fun to try and dig and lay mat when I have 400mm spaced joists to jump between!

    Are any type of gravel/stones particularly better for drainage purposes?

    Also how would I go about installing the weed mat with the stumps and bearers already in place?

    As much as I'm frustrated at having to spend $1k for new boards, it'll at least give me the chance to make it look nice with some picture framed edges and install ballustrade/seating area around the edge. I've also wanted to change the staircase direction and create a landing over the top of the weird square area near the shed that's just an area to store junk. .

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    Quote Originally Posted by r3nov8or View Post
    Re the paving concept and considering keeping the flow from the house level, you could consider laying a cement sheet floor and tiling it. (Others might be able to recommend the specifics )
    I did not even consider this but it might be a good idea for longevity. The only issue would be that tiles + cement sheet + glue would be likely much higher than the current deck boards.

    Also I know nothing about the requirements for tiles that are exposed to the elements 24/7. Would I need to screed the area for flow? I'm guessing at the very least it'd a drain or two.

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    You need fall with tiled sheeting. Expensive exercise compared to decking. If you can re-frame with some fall you won't need screed. Exterior scyon is easy for this and can be gun nailed.
    If you lay weedmat it just doesn't matter that things are in the way, just roll it out neatly and I suggest roadbase on top.

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    Cheapest, longest lasting, solution. The fact that your TP subfloor is perfectly fine, my vote is for TP decking. Even if the original cause remains, it'll be fine.

    You can crack an egg with a sledgehammer too. Just be careful

  42. #42
    Deactivated User Marc's Avatar
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    I once cracked an egg with an excavator. Was hard boiled though

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    My analogy is , if the boards were actually grey gum with no sapwood you wouldn’t be having a problem, the solution is to rip up the boards & redo the decking with the proper durability boards, spacing & new joist protection, there is more than enough ventilation & it isn’t overly close to the ground.
    inter
    ps, at my house I laid a 9 m2 low deck from some leftover durability 1 tallowwood decking, straight on the ground on decking runners at 450 cts, 7 years ago, it greyed and hasn’t changed or deteriorated at all, it is constantly wet & gets hosed off nearly everyday.

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    Appreciate the help here. Certainly reduces some of the uncertainty. I'm up for a bit of money to fix, but fingers crossed it'll be the last time I need to put new boards down for some time to come.

    Looking back I probably should have just paved the area. Would've been better for longevity but at the time I was hellbent on having a pretty deck.
    Also paving would mean I will not have to worry about potential buyers kicking up a stink about no permit etc for the deck.

    Anyway, next time I have some time on my hands I'll install TP deckboards.
    Is there any process I should follow to prepare them? i.e. leaving them out to dry for a few weeks, paint/oil before laying, put some wp treatment etc?

    If i'm reinstalling boards, i'll install a picture frame around the edge of the deck and make a ballustrade to cover the ugly fence, might even turn it into screening.

    Definitely will install with 6mm gaps and take the good advice on installing weedmat & roadbase underneath.

    If I do rent this place out, i'll likely then install a roof of some sort to protect it better, but while i'm here i'll need to prioritise repainting/oiling the deck boards.
    So far to protect myself from sun & rain I have a wind out awning I got for a steal of fb marketplace.


    With regards to airflow - is worth installing some form of vent between the retaining wall and the deck? Are there any options for a vent or opening that people can still walk over?

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    Je pense, donc METRIX's Avatar
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    Quote Originally Posted by YoungBolt View Post
    and also stop the river that used to flow down the courtyard and into the garage at the bottom of the property.
    Does this river still run down to the garage, but it now just runs under the deck ?

    If so, you need to redirect this river away from under the deck using a retaining wall and aggy pipe, as this sounds like why you have a moisture problem under there.

    Here is some info for you on the various durability's of timber, your timber was definitely not one of good quality.

    Timber Durability Ratings

    The durability rating of a species (displayed as a Class) of timber relates to the natural ability of the heartwood of that species to resist decay and insect pests.

    Class 1 Timber Durability

    Class 1 is the highest durability rating.
    Class 1 means that timber is projected to last for 50+ years in a fully protected area and 50+ years outside above the ground.
    Class 1 timber lasts for 25+ years if it is in the ground, such as a deck pole.

    Class 2 Timber Durability

    Class 2 timber also lasts for 50+ years inside and fully protected.
    When it is used outside above the ground, its life expectancy is 30+ years.
    When it is in the ground, its projected usage is 15-25 years.

    Class 3 Timber Durability

    Class 3 timber lasts 50 years fully protected, 15 years above the ground and 8-15 years in the ground.

    Class 4 Timber Durability

    Class 4 timber lasts 50 years fully protected, 5 to 8 years above the ground and less than 5 years in the ground.
    Mieux vaut prévenir que guérir

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    Quote Originally Posted by METRIX View Post
    Does this river still run down to the garage, but it now just runs under the deck ?

    If so, you need to redirect this river away from under the deck using a retaining wall and aggy pipe, as this sounds like why you have a moisture problem under there.
    From my crappy pictures, you might see that the top part of the yard has some grass and paving. This section is held back by a retaining wall that is before the deck.

    I backfilled the entire area with healthy topsoil, installed an agi pipe behind the retaining wall along with some crushed rock & scoria rock. The grassy area seems to drain up a lot of water. on a heavy downpour the grassy area can have pools of water that turn the area into a bit of a mudpool.

    I assume the top section deals with a lot of the old water issues.

    I can only assume the reaosn the soil underneath the deck stays moist/wet is because the lack of airflow and that it receives next to no sunlight. The fence and the 2-3mm gaps between the boards likely dont give much opening to the sun.

    Near the garage I put anouther retaining wall with agi & backfilled the entire area behind it with small size crushed rock, plus there are drains on the concrete before the garage door and shed to take away any remint water.

    Would it be worth installing a drain or agi pipe at the front of the top retaning underneath the deck to catch any excess ground floor?

    I was thinking of maybe using the grate off a drainage channel and install it between the retaining wall and the deck as a bit of a vent to the deck?

    Would it be worth lowering the height of the deck (i.e. creating subframe with joists and bearers at same height) and then installing a space between the retaining wall and the deck? If there's a step then I dont have to worry about people getting their foot stuck walking straight from the grassy area onto the deck.

  48. #48
    Je pense, donc METRIX's Avatar
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    Yes I saw that TP retaining wall, where did you put the aggy at the bottom of the wall, and how much rock did you put on top of it and how wide ?
    Did your pipe have a sock or did you use geotext fabric to stop the soil blocking it.
    Did you have a minimum 1:100 fall of the pipe
    What sized rock did you put on top of the pipe
    How much water comes out of the pipe during / after a heavy downpour.

    If the water is pooling it sounds like it's not getting to the pipe properly.

    Below is the best way to do the drainage to guarantee no future issues, note the geotext envelope not just a sock with soil straight on top of it as many people do.
    Also notice how much aggregate there is, not just a piddly little bit at the bottom of the wall.

    Attached Thumbnails Attached Thumbnails drainage.jpg  
    Mieux vaut prévenir que guérir

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    Quote Originally Posted by METRIX View Post
    Yes I saw that TP retaining wall, where did you put the aggy at the bottom of the wall, and how much rock did you put on top of it and how wide ?
    Did your pipe have a sock or did you use geotext fabric to stop the soil blocking it.
    Did you have a minimum 1:100 fall of the pipe
    What sized rock did you put on top of the pipe
    How much water comes out of the pipe during / after a heavy downpour.

    If the water is pooling it sounds like it's not getting to the pipe properly.

    Below is the best way to do the drainage to guarantee no future issues, note the geotext envelope not just a sock with soil straight on top of it as many people do.
    Also notice how much aggregate there is, not just a piddly little bit at the bottom of the wall.
    ok, haven't done it to the same spec as the picture unfortunately.

    I put the aggy about mid way along the retaining wall. It has a stronger fall than 1:100. It drops about 300mm across a 4m span.

    Admittedly didn't use any geofabric at all.

    Backfilled the rock about 100mm from the back of the retaining wall all the way from the base to about 50mm from the top. Just put soil ontop of the rock.

    Rock was mostly scoria with a mix of some left of 20mm crushed rock.

    I've never checked the amount of water that comes from the pipe. The soil under the deck is fairly dry now. I might soak the area around the retaining wall with the hose and see if the soil under the deck gets wet and if any of the agi pipe drains into the pit it's connected too. A section of the agi pipe is covered by some paving that I mortared in place.

    Definitely will change the way I do retaining walls in the future to include geotec fabric. No one I know who has done them before and gave me advice actually recommended a sock or fabric. Most said that rock is enough around it and 50mm of soil ontop shouldn't be a problem.

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    Quote Originally Posted by intertd6 View Post
    My analogy is , if the boards were actually grey gum with no sapwood you wouldn’t be having a problem, the solution is to rip up the boards & redo the decking with the proper durability boards, spacing & new joist protection, there is more than enough ventilation & it isn’t overly close to the ground.
    inter
    ps, at my house I laid a 9 m2 low deck from some leftover durability 1 tallowwood decking, straight on the ground on decking runners at 450 cts, 7 years ago, it greyed and hasn’t changed or deteriorated at all, it is constantly wet & gets hosed off nearly everyday.
    This.

    If it was poor ventilation and dampness, the Treated pine subfloor would also be showing signs of rot.

    Your solution is realtively simple - goto a decent supplier, buy whatever hardwood takes your fancy (for me that would be either spotted gum or merbau), and re lay it.

    When you are relaying it, 4mm gaps between boards. Treated pine boards look like treated pine boards, they also get more slippery than hardwood, and have 2 advantages only - they are cheaper and easy to hand nail. You've been unlucky with @@@@ timber supply (and yes Ive been burnt buying timber from gumtree or trading post as well - probably all of us have), but dont wreck all that work by putting down pine for the sake of $300

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