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The floor of my laundry room was three layers of hideous vinyl flooring of various vintages, a layer of 3/4" plywood underlayment (to match the height of the vinyl to surrounding hardwood flooring) and a subfloor of diagonal 1x6ish planks.

I removed the vinyl and replaced the rotting plywood. Now I'll cover the plywood with interlocking vinyl plank flooring of this type. The instructions are written for covering an existing flooring material, so they don't address preparation of the subfloor.

Although the vinyl planks are waterproof, it doesn't seem right to lay them on bare plywood, particularly in the laundry room. How should the plywood be prepared? I think I'll just paint with Kilz 2 and caulk gaps and seams.

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I test flooring very oddly. I let 5 or 6 brands sit in a big bucket of soap and water for 3 days. Nothing changed on this brand at all because it is pure rubber. Some others that were supposed to be waterproof yet expanded and held the water - others lost luster or got soft. This definitely won my waterproof flooring tests (just local stores). –  DMoore Apr 15 '13 at 20:26
    
@DavidMoore, I'm so happy to hear about your scientific approach. I'm interested in the complete results from your test, but I guess I got lucky and chose the winner on the first try. –  ArgentoSapiens Apr 15 '13 at 20:29
    
If it says waterproof I better be able to go on vacation and not have to worry about the floor being ruined by water. The TM Ultra did well as well as did builddirect.com/Luxury-Vinyl-Tile/Moon-Rise-Splash/… Everything else I was disappointed. The builddirect website is great and have everything but you have to buy too much for small jobs. –  DMoore Apr 16 '13 at 3:14

3 Answers 3

Your floor needs to be clean and flat for a floating floor. To cut down on squeaking I would have glued and screwed in the plywood.

I am currently putting this floor in my basement. It is a great waterproof material. Not sure where you are going with Kilz2 though.

If you want the floor to be waterproof or have waterproof qualities then the water needs somewhere to go - a drain. If you just want to hold the water on top of the flooring well you could do a paint on waterproofing agent like redguard. I think it is overkill though.

The manufacturer does suggest no underlayment with this - probably worried about moisture trapping under underlayment. If you have large gaps - bigger than a 1/4 inch I would use a leveling agent to fill them. If they are small I wouldn't touch them. If you are looking to trap the water on the top of the flooring so it doesn't get to the subfloor then make sure your planks are tightly clicked, your baseboards are pushed down on the floor and caulk the gap between baseboard and flooring.

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Thanks for your answer; the last sentence is what I'm looking for. Just a few drops of water cause bare plywood to swell up until it dries out. I'm worried about this being trapped underneath the flooring where it'd dry out much more slowly. The idea with the Kilz was to prevent the plywood from absorbing the moisture. –  ArgentoSapiens Apr 15 '13 at 20:31
    
FWIW, plywood should only swell if it's soaked in water and even then, it's mainly on the exposed edges. Particle board, on the other hand... –  DA01 Feb 17 at 22:43

I'd question how waterproof you need this to be. Will there routinely be water sitting on the floor? If not, you may be over-engineering things.

That said, off the top of my head, one option for waterproofing the subfloor would be to paint on Redgard:

enter image description here

It's a 'paint on' waterproofing membrane that you'd typically use behind tiles on cement board and the like.

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I am doing a similar installation now, however my plywood sub flooring is pressure treated. I am filling any gaps with silicone caulking and then using an approved leveling/patching material(Henry Unipatch is what I'm using). I am then going to coat the entire floor with a bonding agent. I have 475 Sq. ft. of floor to do.

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