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800mm High Treated Pine sleeper wall - cladded with decking

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  1. #1
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    Default 800mm High Treated Pine sleeper wall - cladded with decking

    Hi All,

    I've started excavating and am almost at the stage of digging post holes and building the actual retaining wall - just hoping to get some confirmation and advice!

    The wall will be approx 800mm high. Soil is clay with a mixture of solid rock(Sandstone) at parts.

    The plan is to use H4 (maybe even H5 if i can get it in time) Treated Pine sleepers 200x75 for the posts & rails - posts spaced 1200mm apart.
    100mm socked agg drain at the bottom of the wall which will fall towards a pre-existing spoon drain, geofabric to prevent silt and backfilled with drainage ash.

    The biggest issue i'm going to have is getting to the desired depth for the posts (800mm?) - i'm basically on a sandstone rock bed/plateau and will be hand digging/jackhammering all the post holes (no access for machinery).

    I'm also not sure what the best way to set the posts in is (i'm concerned with longevity/rotting) as I've read varying ways to set a timber post that now i don't know which way to go!
    e.g. compacted gravel at the base, then fill with concrete, or concrete pad at the bottom, then fill will compacted gravel etc.

    Basically i don't foresee moving house anytime soon, and i would hate to have to try and replace the wall 10-15 years down the track - i want it to last (especially the posts, replacing rails is easy in comparison).

    I'm tossing up between either using sleepers as posts OR going down the path of getting steel H posts/channels - the only thing that's putting me off this is the price, but more so the fact that I've never used this before and i imagine i'd have to get the heights dead on when setting them in?
    whereas with the sleepers i was just going to get 2.4m sleepers, set them in and at the end snap a line and cut them to height with the circular saw.

    Can cutting posts after the fact be easily done with steel channels (angle grinder, then cold gal spray to cover the cut??).

    The whole wall will be cladded/faced with 86mmx19mm spotted gum decking boards running horizontally.
    If using sleepers for posts i was just going to screw another sleeper in between the posts (e.g. every 600mm) and attach boards to this.
    Or if steel posts then just batten out the wall (attach some treated pine vertically to the sleepers) and attach decking boards to that.

    Any advice would be greatly appreciated!!

  2. #2
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    galvanising and treated pine dont go together well.
    id just go treated pine all the way.
    read this
    https://www.google.com.ph/url?sa=t&s...G-f19crdO6X_Op

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    if u are cladding it i think there would be a better way to fix the boards than tight up against the treated pine.
    i worry about the large surface area squished up against the soft rough sawn pine backing up against dirt. this is a good scenario to promote rot in the decking boards.
    i might be getting a bit pedantic, but you want it to last and the risk is very real.
    perhaps run some rough sawn 50x35 or whatever they are down the posts first then attach the deck boards therough that.
    that way there is less surface area contact and less chance of rot.

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    use stainless screws for the deck cladding and treated pine square drive coach screws for the posts to sleepers. make aure the back is lined in black plastic and backfilled slowly and compacted every 100 mm of backfill.

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    Thanks for the replies rebuilder!

    Yeah that's a good point - i didn't really think of the excess contact of the decking boards touching the sleepers - i'll batten it out so there is less surface area contact.

    I'm either going to face screw with 60mm square driver stainless decking screws as you've mentioned, or use hidden fasteners (camo system also in stainless steel).
    When concreting the timber posts should i add gravel at the bottom, or just concrete the whole lot (and slope the top off)?

    Is there a reason to use black plastic lining the sleepers? i thought it might make it harder for the sleepers to dry out? As i'm going to be cladding i'm not worried about soil staining the sleepers.

  6. #6
    4K Club Member Marc's Avatar
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    From your post it seems you are thinking in not digging all the way down to 800. (?)
    A few considerations.
    Clay is hard to dig up but when it rains it is soft, the post lean, the ground shifts. You say 800 high, but how much higher does it get behind your wall? Or is it flat all the way?
    If you are going to use sleepers as post, don't use 75mm. For $6 extra go 200x100x2.4
    A pine sleeper flat against the wall is not a strong post. If you want to build a strong wall that lasts you would need to use two post separated by 150mm and on the edge.
    Usually besides public works. no one builds that way. I understand.
    If you don't want to or can not dig 800 down, you can rain the post in with a stay rod. You will need access to the high side and dig a trench for the rod and to concrete in a steel cross member. The rod will need to go minimum 2.4 meters back (3 times the hight)
    There is nothing wrong with using galvanised post. Clearly a better choice. Stronger, no issues with it's position, no rotting in the ground, no debating how it will be anchored in the hole, and absolutely no issues with the treated pine. Paint the section that goes in the concrete with bituminous paint and also the inside of the channel where the TP goes. You can also paint the ends of the TP with the same paint to avoid the treatment to contact the zinc, no longer a big issue with todays TP.
    That would be my choice any day.
    And don't skimp on the hole depth. Don't use quick set concrete. Use high strength concrete mix if you are going to buy the bags or mix your own 3/2/1, if you need to cut the steel beam, set the cut end in the concrete and leave the top galvanised and uncut.
    Best of luck with your project and post plenty of pictures.
    “In the fields of observation chance favors only the prepared mind.”
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    well yeh im sure the old galv cca issue was due to the a part, arsenic, which i dont think exists these days. Steel companies still specify the issue, and fastener companies still say to not use galv fixings in treated pine.
    marc are you sure this is all completely obsolete?

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    im going to answer my own question with this link.. perhaps its not an issue if u coat the pine, but it wouod have to be moisture proof, and durable enough to withstand the movement of the pine against the galv, which woukd wear it out. something i cant imagine existing. especially not with tonnes of dirt pushing against it.
    im quite sure galv and cca is still an issue current day.
    https://www.google.com.ph/url?sa=t&s...072nH7CO7lhjv2

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    Quote Originally Posted by Marc View Post
    From your post it seems you are thinking in not digging all the way down to 800. (?)
    A few considerations.
    Clay is hard to dig up but when it rains it is soft, the post lean, the ground shifts. You say 800 high, but how much higher does it get behind your wall? Or is it flat all the way?
    If you are going to use sleepers as post, don't use 75mm. For $6 extra go 200x100x2.4
    A pine sleeper flat against the wall is not a strong post. If you want to build a strong wall that lasts you would need to use two post separated by 150mm and on the edge.
    Usually besides public works. no one builds that way. I understand.
    If you don't want to or can not dig 800 down, you can rain the post in with a stay rod. You will need access to the high side and dig a trench for the rod and to concrete in a steel cross member. The rod will need to go minimum 2.4 meters back (3 times the hight)
    There is nothing wrong with using galvanised post. Clearly a better choice. Stronger, no issues with it's position, no rotting in the ground, no debating how it will be anchored in the hole, and absolutely no issues with the treated pine. Paint the section that goes in the concrete with bituminous paint and also the inside of the channel where the TP goes. You can also paint the ends of the TP with the same paint to avoid the treatment to contact the zinc, no longer a big issue with todays TP.
    That would be my choice any day.
    And don't skimp on the hole depth. Don't use quick set concrete. Use high strength concrete mix if you are going to buy the bags or mix your own 3/2/1, if you need to cut the steel beam, set the cut end in the concrete and leave the top galvanised and uncut.
    Best of luck with your project and post plenty of pictures.
    Cheers Marc!

    Above the wall is lawn which its not level and dips all over the place. The highest part is 800mm from the base of the wall, so i'm going to do the wall 800mm high and eventually level the rest of the lawn out.

    The clay isn't too bad - the jackhammer with a spade bit makes life much easier. Its more so the solid sandstone plateau at parts (Our house is on a hill and theres sandstone in most places when i dig :/ ).

    I was aiming to dig 800mm deep, though wasn't sure if i could get away with 600mm deep in the solid sandstone - i guess 200mm isn't really much more to go so i'll just have to man up and get to the 800mm

    Good point on the 100mm posts - if i do pine posts i'll go 200x100 for the posts and 200x75 for the rails.
    Going to ring around tomorrow and price up steel posts - if they aren't ridiculously $$$ i'll probably go for them.

    If doing pine posts, do you just set them straight in concrete? (e.g. no gravel base).

  10. #10
    4K Club Member Marc's Avatar
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    The answer to timber post in concrete is not as simple as do this or that.
    If it was under cover, clearly post in concrete is best since water ingress is unlikely. In your case, you can say, gravel on the base and concrete around the post will facilitate drainage from water that may ingress from above between timber and concrete.
    I say in your case there is more likelihood of water coming from below at 1.6m under ground and go straight up through the gravel and in the timber. So what is the best way to do this?
    I say the best way is to use steel post or concrete post or ... if you really must use sleepers, have dual post on the edge packed in gravel leaning against half sleeper across the post in the ground to take some of the pressure, all dutifully painted with tar.
    (Did I say concrete post? Oops! Yo are not in Victoria are you? If not, disregard my last blooper)
    A lot of work and at $35 a sleeper you may as well pay $70 for steel H post.

    PS
    Just an illustration, If I need to put a pile in the river bank, I try to get the highest grade treatment I can find (H5 or H6) and then I cote the part that goes in the sand and up the the high tide mark with polyester resin and fibreglass. A coat of resin, followed by fibreglass stuck on the fresh resin and stapled to it. Then two more coats of resin.
    “In the fields of observation chance favors only the prepared mind.”
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  11. #11
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    Quote Originally Posted by Marc View Post
    The answer to timber post in concrete is not as simple as do this or that.
    If it was under cover, clearly post in concrete is best since water ingress is unlikely. In your case, you can say, gravel on the base and concrete around the post will facilitate drainage from water that may ingress from above between timber and concrete.
    I say in your case there is more likelihood of water coming from below at 1.6m under ground and go straight up through the gravel and in the timber. So what is the best way to do this?
    I say the best way is to use steel post or concrete post or ... if you really must use sleepers, have dual post on the edge packed in gravel leaning against half sleeper across the post in the ground to take some of the pressure, all dutifully painted with tar.
    (Did I say concrete post? Oops! Yo are not in Victoria are you? If not, disregard my last blooper)
    A lot of work and at $35 a sleeper you may as well pay $70 for steel H post.
    Haha nope not in victoria, in NSW!

    Yeah gal channels definitely sound like a lot less work and less things to worry about.

    Below picture shows part of the wall to retain, it does return back in a couple of meters on the right. (I'ts an L shaped wall, with the return part then transitioning into a rock wall).
    The section on the left that goes into the lawn will be stairs.

    Still a bit of digging/clearing out to do (theres a lot of rubble which was placed behing the original rock wall), then onto the post holes - hoping to get it all done this weekend and ready to set posts the following weekend!
    Attached Thumbnails Attached Thumbnails retainingwall.jpg  

  12. #12
    4K Club Member Marc's Avatar
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    That ground looks more sandy rocky than clay. A bit of clay to the right and may be when you dig down?
    That is the sort of ground that shifts when you get a lot fo heavy rain. Fortunately the gradient is not that steep behind your wall but certainly not flat!
    Good decision about steel post. Do paint the post and the sleepers. It is true that copper can react with the zinc but it's more a problem in coastal areas and less likely with LOSP
    “In the fields of observation chance favors only the prepared mind.”
    Louis Pasteur



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    The section on the right of the photo is sandstone (the pile near it is part of it that's been jackhammered up) - but yeah most of the soil behind the wall i believe is fill/not natural ground, mixed in with lots of rubble (crushed concrete, rock, bricks, roof tiles etc). The natural ground that I've dug in (i started to dig some post holes for where the stairs will be) has mostly been partly clay and rock.

    The ground that you can see at the base of the wall is 1/4 minus (mixed in with dirt that come out of the wall). Pavers were previously on this section, plan is to dig this down a bit after the wall is done and pour a slab + tile.

    Wouldn't happen to have any suggestions for steel post suppliers would you?

  14. #14
    4K Club Member Marc's Avatar
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    Not really, but plenty of suppliers in Gosford
    “In the fields of observation chance favors only the prepared mind.”
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    i misses something, LOSP, where do u get losp sleepera from? ive only ever seen green rough sawn sleepers (CCA).
    and sticking them in the ground next to what looks like a river?? in that wet environment is bound to leach it out onto the galv.
    haha sorry marc, i can see u are very anti pine in ground, and i can agree that its not ideal, but a concreted rusted steel H beam is much harder to remove and replace than a rotted timber poat sitting in front of the wall.
    doesnt LOSP only go uo to H2 category? surely h2 wouldnt suffice for in ground use.

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    and with the required minimum h4 for in ground use, we would have to be looking at CCA and at h4 levels, there is enough stuff to leach out for years and screw these posts.
    can u get concrete posts for this.

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    and finally, painting it with anything, will actually make it worse. if there is a tiny scratch in the paint and a small portion of the anode, in this instance, zinc, comes into contact with copper, the reaction is worse than if the copper came into contact with a larger surface area of zinc.
    the conductive groundwater in the soil will quickly help the electrolosis on its way to work its way through the small zinc opening and the spread out sideways and destroy ur galvanized post from the inside.

  18. #18
    4K Club Member Marc's Avatar
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    The OP will confirm but the only river here was mentioned by me as an example of what I have done with timber post in extreme conditions. An ordinary retaining wall with logs or concrete or steel down 800mm will last like a fart in a basket if it is set in a river bed. .

    I did not say that logs are treated with LOSP. I said that with current treatments the problem with galvo is less that it used to be and even less with losp.

    As far as your idea of how galvanic corrosion will work between a galvanised post that is painted with bitumen and a log that is painted with bitumen and the remote likelihood of contact I wonder where did you get that? And how do you figure that will work unless submerged or in a coastal area with high saline spray all day long? Galvanised bolts do corrode inside TP when in a wet environment. That is why I suggest painting both. The speed of the oxidation process of zinc in contact with copper oxide depends from the concentration of copper oxide and the electrolyte present that is water and salt. The mass differential typical of zinc anodes on boat hulls or bimetal problems like with stainless steel and galvo is a completely different problem and does not apply here.
    “In the fields of observation chance favors only the prepared mind.”
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    i got the information from my protective coatings experience, not from a particular source, but yes there is one thing missing from my equation, salt.
    but the problem i was talking about with any coating, is that if it is scratched, the corrosion rate is worse than if there was no paint at all.
    nonethe less i think i agree now that without salt my arguments may be null and void.
    also, on this point, if u do go galv h posts, dont fix the spotted gum to the galv, thats just asking for trouble.

  20. #20
    4K Club Member Marc's Avatar
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    I once had to brace a few pylon that had been attacked by Teredo worms and thought that HDG lintel would be OK in brackish water with 6 0/00 salt content as opposed to 35 0/00 in sea water. I was wrong. The zinc was attacked so quick that in a few years there was no more coating and the angle was a big lump of rust. Should have bolted a couple of boat anodes to it but I didn't.
    Should see what sea water spray does to metal structure like balconies or windows. It's like spraying them with sulphuric acid.
    Talking about acid, wood, particularly hardwood, has a lot of acetic acid that can contribute to metal corrosion even without any contact, particularly inside shipping containers where it becomes volatile.
    But back to this retaining wall, the HDG UB and TP sleepers is a proven way to build a small wall and easier than using wooden post. In my experience anyway. others favour wooden post, and some even concrete post. (Oh my ! )
    Tell you what.The best post to use on a wall like that is railway line. Will rust, but all you do is give the lot, steel and timber a splash of sump oil every year or so. Will last 2 life times
    “In the fields of observation chance favors only the prepared mind.”
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    Thanks for the info fellas.

    I've been doing some ringing around - hoping to source them locally, though some places are really pricey $$ (especially for the corner posts - its about $100 for a 1.8m corner post.... i need 5 of those, plus H channels and C channels to go with it!).

    I was planning on ordering 1.8m posts, digging holes 800mm and setting them in, then once they're set - snap a line and cut them to height and touch up with gal spray.
    One particular brand which seems to be the most widely available (Retain-IT) only offer upto 1.5m lengths - these can be ordered through some of the big hardware chains and are a fair bit cheaper then some of the other prices I've got.

    If i went with 1.5m gal posts, they could only be set 700mm deep (they will be 800mm above ground) - do you think this would still be okay?
    If i can go 1.5m lengths then it'll be cheaper and more readily available, as opposed to the 1.8m posts.

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    i had to build a retainig wall to hold my block up after 30 years of sand pushing down on nothing but the hardifence whixh the builders uses as a retaining wall. i went with the concrete posts and panels because it was all hidden by the neighbours fence. the wall had to be 600 high, but like u i couldnt get below 500 cm. i just made the concrete foundations super large and it is still at andng to this day holding up loose sand which used to just run down into neighbours yard. I think as long as u are actually concreting the sides of the post amd not juat gravelling it, u should be right.

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    but i think, as marc mentioned, u might want to have the posts no more than 1200 apart if thats the case.

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    Quote Originally Posted by rebuildr86 View Post
    but i think, as marc mentioned, u might want to have the posts no more than 1200 apart if thats the case.

    Cheers! Yep posts at 1200 centers is the plan.

    Best price I've found so far is $764 (5 H channels, 2 C Channels and 5 Corner posts all @ 1.8m) though its 2+ hours away, so a 4 hour round trip (delivery is $200).
    Hoping to find something similar in price locally - hopefully be able to get the 1.5m White Retain-IT posts for cheaper. Tried getting onto the special orders desk at bunnings but they never called me back... standard!!

    Has anyone used the Whites ones/know if they're hot dipped gal? i couldn't find any mention of them being hot dipped gal which is kind of off putting....

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    You could make your wall 750. 50 mm means nothing, 100mm missing underground on the other side ... I am not an engineer but it surely means more than missing 50 mm on the hight of the wall. Plus you will not need to cut the post. That must be a plus!
    Bunnings special orders?
    “In the fields of observation chance favors only the prepared mind.”
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    Steel posts have been ordered - can't get them for 2 weeks though.

    Haven't made a lot of progress on the wall - a large section of sandstone has really slowed me down, though thankfully its now pretty well ready to start on the post holes next weekend!

    At least 2 to 3 (possibly more) of the post holes (11 all up) are going to be into solid rock, - after jack hammering out a large section of sandstone i'm starting to worry about trying to get to 800mm deep in those parts.

    I only have the weekends to do this and time is not really on my side - any suggestions/alternatives if getting to the desired depth isn't feasible. I'll have a crack next weekend and see how slow it is, if it feels like its going to take 1/2 to a day to do just one hole in the rock, i might have to rethink my approach.

    Would something like chemical anchors set in a shallow hole e.g 400-500mm deep concreted in with the post be okay, this way it'd effectively attach the post to the sandstone plateau/rock? Or another idea was to hire a core driller and core drill the post holes and set in concrete (though at $200 for the day :/).

    One section will only be retaining 200mm of top soil, the other 600mm is solid sandstone, so its just the water it will have to deal with (which hopefully the ag pipe makes short work of).

  27. #27
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    Intuitively if you have a hole in sandstone it is different from soil, the question is how much is enough and that I don't know.
    You could hire a dingo with a jackhammer attachment.
    “In the fields of observation chance favors only the prepared mind.”
    Louis Pasteur



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    Just an update - am pretty much half way through the post holes - progress has been really slow, all up I've probably spent 1.5 days to dig 5 post holes. 6 more to go!
    2 of them the first 300mm was soil, then the last 500mm was rock. All the other post holes have just been complete rock which has taken between 2-3 hours per hole to jack hammer down to 800mm deep. snapchat-1679941012.jpg

    Below pic is of one hole (only about 300-400mm deep at this point), thinking for this one i could get away with just going 600mm deep as its not really retaining anything (pretty much all solid rock behind it).

    img_20171204_142629470.jpgimg_20171204_142625579.jpg

    Picked up the gal retaining wall posts, they're heavy bastards - seem very solid, only downside is the inside of the channel is 85mm-90mm(can't remember exactly, but atleast 85mm) and i'll be using 75mm sleepers.
    I need them fixed in as i'll be battening them out to screw decking boards to. Not sure if i should just put window packers in the channel to fill the gap, and also attach one screw through the gal post into the sleeper to hold them in.

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    well, progressing is progressing!

    keep it up!

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