Sealing Plywood

[Pappy]

My work deck took some bad water in the flood and needs to be replaced. Plan to use 3/4 T%G plywood subflooring. Before I put it down I want to prime/seal the bottom and edges and then a couple of coats on the top after it is down. I know it won't stop heavy water but just want to seal out the light moisture to make it last a little longer.

Also thought about laying a sheet of cheap vinyl on top with drip edging around it. Any guess how the vinyl would hold out exposed to the weather?

[Stytooner]

I think your better bet would be 3/4" treated plywood. Then seal the top with Thompsons every year or so. That would last a very long time. At least 10 years and more.
5/4 treated decking boards would be a second choice. If it is screwed down, it too can last many years. Indoor sub flooring is not designed to get wet at all. The humidity will separate it eventually I think even if properly sealed.
If you can find vinyl that has a UV protective coating, that might last awhile, but standard cheap grade flooring stuff won't hold up too well to the elements.

[cwsmith]

I second the 'treated' plywood.

At minimum, you surely want to use an 'exterior' grade ply which utilizes moisture-resistant adhesives to hold the plys together. All the second-hand things you do to protect interior grade will not be as good or as long-lasting as the factory processes of 'exterior grade' or better yet 'treated' plywood.

From my limited experience, a vinyl covering just won't hold up. Over time it will weather and at minimum become porous. As I understand it, once that happens, it's almost worse than no covering, as it will then trap moisture in the wood.

I hope this helps,

CWS

[capncarl]

The bad thing about putting a seal coat or vapor barrier is that it can potentially hold water in the wood and completely defeat its purpose. To seal plywood your must make it impermeable to water. something like thompsons water seal may work better than a barrier or paint type coating. Don't spare it, really let it soak in. For flooring it should last a long time on the bottom of plywood as it will not be subjected to sunlight, rain, or other elements.
capncarl

[schloff]

I was tasked with a similar issue a few years back, only with a wheelchair ramp rather than flooring. My solution was to use an automotive undercarriage coating. Relatively inexpensive at any auto parts store ($6-ish or so) for a small job, but not sure how much you'd need for multiple sheets of plywood.

I would definitely use a treated sheet good for starters, it's only a few dollars difference per piece. Maybe adding $30 to the whole project, not knowing the size of the floor being replaced.

[radhak]

Better use external ply.

I used internal ply to build a kids picnic table, sealed the edges with epoxy, then painted it all with internal/external paint. But within 6 months it started showing frayed edges, and around 15 months later I had to trash it all.

[Pappy]

I have the contractor desk at the local McCoy's Building supply looking for some pressure treated T&G 3/4 ply to keep the joints smooth. Hate the thought of having to cut a spline around 2 or 3 sides of 6 sheets of plywood.

I used treated ply once but didn't seal it. Results were less than satisfactory. I will go with Thompson's this time. How long do I need to wait to seal what will be the underside and edges before I can lay it down?

[Stytooner]

I would say that you can seal it with Thompson's and let it dry a few hours. Then lay it down. If you aren't using treated lumber joists, I would seal them too at the same time. Don't use the Thompson's sparingly. Apply it like you mean it.

[cwsmith]

Pappy,

Do you really need to use plywood for your work deck? Have you considered just using treated 5/4 deck lumber instead, and other PT for joists, etc.? My 18 x 25 deck is now almost 30 years old and I've never done anything to it. We just like the weathered look, so it's never seen stain or water seal. Some of the deck boards are checked bit, but it's just as solid, plumb, and level as the day I built it.

No workable basement at that house, so I used to drag everything out on the deck to do any woodwork at all. The 5/4 with 3/8" spacing provided good surface for any tool setup and for my folding benches, etc.

So, not only sturdy, but pretty much maintenance free and no concerns about water pooling after a rain etc. Up here in the northeast, we also see a lot of snow for a few months each winter. About all that did was cause a handful of nails to set a little proud each spring and I'd spend a few minutes setting them back down.


CWS

[Pappy]

Pappy,

Do you really need to use plywood for your work deck? Have you considered just using treated 5/4 deck lumber instead, and other PT for joists, etc.?
CWS

Some of the tools are on 3" or 4" casters and the deck boards wouldn't be a problem for them. The band saw, edge sander, and jointer ride on 2" Darnell rose casters and the spaces coupled with the rounded edges would make them nearly impossible to move. Add to that the idea of dropped washers, screws, etc. going between the boards and the plywood seems a better idea to me.

[capncarl]

Hearing all.this reasoning, it may be better just to change a couple of sets of casters rather than going with a building material that will self destruct in a couple of years and have to be re-done again!
capncarl

[iceman61]

Whatever material you decide to use, treated wood needs to "season" out (dry out) for 2-3 months before you put any type of paint or weather protection on it or you stand the chance of it peeling back off.

[JoeyGee]

Hearing all.this reasoning, it may be better just to change a couple of sets of casters rather than going with a building material that will self destruct in a couple of years and have to be re-done again!
capncarl

This is exactly what I was thinking.

[Pappy]

Changing out the casters is not an option. The mobile bases on 2" casters are a version of the Wood magazine design and would require a complete redesign and rebuild of the bases. And there is still the issue of dropped hardware in a deck with boards.

McCoy's found a source for the 3/4 T&G at $42 a sheet. A bit pricey but still my best option. Depending on how dry it is, I may skip treating the underside and just seal the top after it dries out.

[cwsmith]

Pappy,

I understand you challenge with smaller casters or those little roller bearing-type coasters... on a spaced-deck boards it would be less than desirable. At the time when I had only my deck to work on, the only stationary tools I had to deal with was my RAS and BT, both of which had 3-inch wheels. Biggest problem for me was the constantly changing weather, which here in NY's southern tier, can be frequent (like we say, "If you don't like the weather... wait a minute!"). So, all my equipment of the time was quick-fold tables and hand-held tools and a few tarps.

Regarding the "dropped hardware", I don't recall whether you work surface is flat close to the ground (like a 2 x 4 supported platform, or whether it is actually raised a foot or more off the ground.)

My deck was at its highest point about 5 ft off the ground (and at the lowest, nearest the house a 1-1/2 ft.). So when I dropped my first drill bit, I never did find the darn thing. After that, I placed a couple of tarps under the deck, with ropes at the corners.... hardware was then easy to find and retrieve, as I could just pull the tarp out and then from the other side pull it back into position. However, anything larger than a 1/4" or so simply wouldn't 'fall through the cracks'.

My present shop is in my basement where I've installed 'Dri Core' OSB tiles. While the dropped screw or bit isn't lost, it's a lot more difficult to find than out on that deck, where I could just look at the tarp under the deck (it almost acted like a safety net, The OSB is almost like camouflage and I spend too much time on my knees with a flashlight and my face close to the floor. The next shop will have a solid color floor I think.

In any case, I understand your challenge and you pretty much know what works for you and what doesn't.

CWS