I am laying a plywood sheet floor in my shed. I have plywood that is certified for humid conditions rather than wet and the sticker on it also says that the edges and faces should be sealed. It is not pressure treated.

I expect the floor to stay dry as it is not in full exterior conditions. Similarly it is not in direct ground contact and is well ventilated underneath and will rest on pressure treated timber supporting beams. The beams will rest on bricks with a plastic layer between them to stop any water being wicked up from the concrete slab.

I wondered if it is worth sealing the faces and edges of the plywood to protect them if they are exposed to any water and from moisture in the air. I already have water repellent shed and fence coating paint (but it has waxes so not ideal for a floor or for overcoating) and basic multi-surface primer as well as interior wood paing and lots of old interior emulsion. What is good/sufficient for sealing the edges of plywood? I have considered and excluded epoxy sealer as overkill for this job.

  • Hello again. This may be a "product request", and so off-topic here, but let's see what answers you get. Feb 7, 2020 at 13:06
  • Thanks for leaving it alone :) really the question is do I need to seal it not what should I use, as the answerers have interpreted rightly. Feb 8, 2020 at 10:44

1 Answer 1


Do you need to seal the faces? Not really in the conditions you described. I have worked in a plywood plant and all the product used the same glue. The difference was the quality of veneer and if any holes were plugged , and later filled and sanded. The last step they did spray the edges and put the company logo on the side of the unit. Painting the surface will be plenty of protection, paint will seal from moisture and mud on shoes and actually provide some wear protection. Sealing the edges won’t hurt but really is not going to make much a difference in your conditions.

  • 2
    I agree. I've build and used several yard sheds with treated lumber floor framing and untreated BC plywood. It's quite humid here in summer, and there's not been any sign that air moisture degrades the plywood after many years. Of much greater concern will be rainwater, snowmelt (from equipment storage) and spills. I used two coats of floor varnish (urethane) after installation and before wall framing.
    – isherwood
    Feb 7, 2020 at 16:41
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    Is it necessary, Maybe not. Would it be worth it for peace of mind, Probably. You could Use end cut sealer on the edges, cut edges at least. lowes.com/pd/…
    – Alaska Man
    Feb 7, 2020 at 18:38

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