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Advice on remediating moisture damaged shed floor (WBP Plywood)

  • 22-04-2022 9:45am
    Registered Users Posts: 82 ✭✭ Tr1ckieD1ckie

    Just finishing a DIY shed build. All has gone well except that over last winter the WBP laid on my floor were subject to significant water ingress as the shed wasn't watertight until recently. They seem to have dried out quite well but are still a bit spongy in places and not as rigid as previously.

    I laid the floor frame 4*2s on blocks with insulation boards in between and these are sealed with aluminium foil tape.

    Damaged WBP ply (18mm) goes over this (couldn't afford marine ply at the time but now regretting I didn't invest!) which run over the entirety of the floor frame.

    Problem is my 3*2 wall frames sit on top of the damaged WBP so it's not trivial to remove the WBP (roof is built on top of wall frames /walls clad etc.)

    So my question is am I ok to lay new WBP 18mm over the existing ones to achieve a rigid floor (would OSB3 be better here) or would I be better to take them up and replace them- it would mean installing additional floor joists to support the ends of the boards as I can't get under the wallframes now. And if laying a new layer over the existing ones, is there any value in installing a layer of viscrene in between.

    Grateful for any advice here

    Thanks folks


  • Registered Users Posts: 30,702 ✭✭✭✭ Lumen

    It's probably delaminated and warped.

    Is it spongy all the way to the edge?

    Fiddly to flush cut so it you cut it out with a circular saw and install new boards bearing on new sistered joists you'll be able to see the old edge.

    Have you tried not giving a ****? 😀

  • Registered Users Posts: 82 ✭✭ Tr1ckieD1ckie

    many thanks- it's completely solid at the edges but spongy at some joins between the boards in the middle of the floor- which is why I thought I might get away with laying another layer over the existing one and screwing this layer through to the floor joists (acknowledging that at the outer edge it will just have to sit over the existing layer

  • Registered Users Posts: 30,702 ✭✭✭✭ Lumen

    Right, the question is whether the current ply has swollen to the extent that an additional layer won't sit flat, which determines whether you have to cut out the existing ply or not. Unfortunately even a mm or so of uneveness in a ply floor is quite easy to detect, it's amazing how good the human brain is at finding faults!

    I have had some success with using thin sheets of woodfibre to shim out the gap between two layers of flooring, so I wouldn't rule out bodging, and I think in your shoes I'd be a bit wary of cutting out the whole floor.

    When considering appropriate floor material, IMO it matters more how it's treated than what the quality of material is. Were the cut edges sealed before going down? I suppose it's a bit late to be going over that though. Regarding OSB vs ply, depends on what you're using it for. Ply is easier to sweep, and less of a disaster if it gets wet (as long as the edges are sealed). But it's so expensive right now...

  • Registered Users Posts: 82 ✭✭ Tr1ckieD1ckie

    Many thanks Lumen. Great idea about the wood fibre underlay and I see screwfix sell this. Didn’t cut the boards laid them as 8*4 sheets and frame made to fit that but I didn’t think to seal the edges. I did varnish the boards themselves but only to limited effectiveness. That sounds like a plan then. Any value in Visqueen between the old and new boards. I don’t particularly want to trap moisture either though. Thanks again for the advice

  • Registered Users Posts: 30,702 ✭✭✭✭ Lumen

    Is Viqueen a vapour barrier? If so, don't think so. Are you trying to stop draughts?

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  • Registered Users Posts: 82 ✭✭ Tr1ckieD1ckie

    It is indeed lumen heavy duty black polythene