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Spotted Gum Deck Issues

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  1. #1
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    Default Spotted Gum Deck Issues

    Hi All. I’m new here and hoping for some advice. I bought a house which has a spotted gun deck with about 2-2.5 mm spacing. Within 1 year of moving in it warped in some places and had black ‘streaks’ through it (it was only about 1 year old then). We oiled it regularly but it looks pretty bad. The deck is mostly exposed to weather and abuts the walls of the house. Many ends seem to have already started rotting due to moisture although the deck is now only around 6 years old. The boards are 135 mm wide and the deck is 200 mm high over clay soil. Hoping to sand and redo the boards to give them some more life (there is a LOT of deck) while we try to negotiate some reasonableness into the person that build it and try to get it rectified properly.

    Just wondering, is there some standard or other guide re spacing for decking boards?

    Will oiling (after sanding) the sides, underside and top give it extra protection from the elements or should we use something else on the ends and underside?

    Joists are just covered with the pvc - is tape or paint better? Given the soil moisture under the deck and the bearers form part of the house - need to do this properly but not sure what the standard / practise is.

  2. #2
    4K Club Member Marc's Avatar
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    What you are suffering is from low deck syndrome.
    200 mm is inadequate for ventilation, so the underside of the decking boards have constantly higher moisture than the top side and therefore the board cup.
    Also at 135mm wide, you need them to be a minimum of 25mm thick if not 32, and I bet they are 19. Hope to be wrong.
    2 mm spacing is way too close, but ... it is possible that it wasn't the case when first built, and it closed up due to excess moisture.

    Digging out some soil from under the deck would make some difference but with only 200 mm I suppose that would be rather hard to do.
    A roof over the deck would solve most problems but easier said than done.
    Sorry, not much help here.
    Science is never settled,
    it advances one funeral at the time.
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  3. #3
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    Thanks Marc. Looking at roof over decking. Yep, soil is an issue as well but very difficult to rectify from the looks of things. 👍

  4. #4
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    3mm is minimum on 90mm boards, wider boards need around 4mm, these should open up to around 5mm after some time.
    A deck which has no airflow under it will always be problematic especially if it's exposed to the weather.

    Moisture will build up under the deck and cause all sorts of issues, timber does not like uneven moisture from one side to the other.

    Do you have any pictures.

    Does sound odd, that after only such a short time the ends are rotting as spotted gum is a very hardy timber.

    Where are these ends, at the exposed end or butting the house, how close are they to the structure.

    Here is a good document with useful information.

    https://www.qbcc.qld.gov.au/sites/de...ecks_final.pdf
    Mieux vaut prévenir que guérir

  5. #5
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    I tried posting some photos from the iPhone but not uploading for some reason. The ends which are the most warped / rotting are abutting the exterior of the house in an unsheltered location

  6. #6
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    25fd728d-0b20-4bf1-a0e5-7351ba806102.jpeg70beff07-e6bd-4cdb-ae56-2c76d05ed692.jpeg
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  7. #7
    4K Club Member Marc's Avatar
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    What is that?
    Besides very poor workmanship it shows a monstrous gap, uneven finish yet no cupping nor rot. It looks like part of a pallet to me.
    If those boards are 130, that gap is 20mm
    Science is never settled,
    it advances one funeral at the time.
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  8. #8
    Je pense, donc METRIX's Avatar
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    Quote Originally Posted by FixerUpper15 View Post

    Hard to tell from those pics, where is the rot, they just look like badly cut ends of the board, do you have a pic of the tops of the board and one of the endgrain.
    Also one of the joists, you mentioned there was PVC put over the joists, have you got a pic of this as well, also from the side of the deck, is there any way air can get under the deck, ie has the 200mm gap been enclosed this way we can see what might be going on.

    Were stainless screws used to hold the boards down ?, the blackening of these timbers is usually caused by steel, not stainless steel.

    What oil have you been using, and how often is it applied, did you ever strip the oil off over the 6 years and start fresh,
    Mieux vaut prévenir que guérir

  9. #9
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    Sorry should of clarified that those are the boards taken off the deck and sanded back before painting. I’ll get a photo of the actual deck and post later.

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