I built a 12'x20' shed foundation on the Oregon coast last Summer. It is 3/4" pressure-treated Doug Fir plywood over P-T framing. The plywood was very wet when purchased and installed wet like most PT woods. I still plan on installing a lino or laminate floor over the plywood once finished. I plan on erecting walls when I return in the Spring. A neighbor told me that water has now leaked under the 10 mil Visqueen cover and is puddling in places. The sheets are screwed 6" O/C in addition to construction adhesive at all framing members. Will this standing water damage the plywood very much if I don't re- wrap it before spring or am I OK?

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    It's not so much that it's pressure treated as that it is plywood. Plywood will eventually delaminate when the glue dissolves; and that will have to do with how thick the laminates are; especially the one on top. You will also probably get some deterioration along the edges. Here are some reviews on a similar product from Home Depot customers: homedepot.com/p/… – sborsher Dec 24 '14 at 18:51
  • Thanks, I've seen that HD product and it looks bad right off the stack. Hopefully my Doug Fir plywood is a bit more resilient as I have never had good luck with the Southern Pine products either such as T-111 siding. I might have a neighbor pull all the visqueen and reattach a better tarp since the house is over 500 miles from me. It rains so much up there during the Winter I doubt I will have any luck drying it out first before re-tarping. Since it's just a shed it's not too critical but I would sure hate to drop a foot through the floor next year if it is going to rot over Winter. – TurboToad Dec 24 '14 at 20:23
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    I agree with @sborsher. Experience shows me treated solid wood is better than treated plywood. My treated plywood which was under a deck (to make a storage area) started delaminating after 3 years outside in Michigan winters. I will never use plywood anything exposed to the weather again. – Bulrush May 9 '16 at 23:40
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    So, it has been almost 2 years since you first posted. What has happened? – wallyk Nov 27 '16 at 6:43
  • It depends on the type of plywood on how long it can handle being wet , the plywood mill I worked in used glues that when heat cured no amount of water could cause delamination. (Springfield Oregon). – Ed Beal Jun 12 '17 at 18:44

Once you have built the walls with plywood installed & roof completed windows cut out & entry door framed, the wet treated plywood floor will start to dry up. Purchase a moisture meter, test each treated floor sheet until the meter shows low moisture. Then install 4x8 sheets for a finish floor, particle board or 3/4 ply untreated and whatever after that. You're good to go.


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