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Waterproof paint over plywood

sdr1's picture

Ok fellas I goofed and used the wrong plywood on a personal project a few years ago that is exposed to the elements. Long story short the ply is delmaninating. I've replaced a couple bad pieces but would like to coat the entier project with a waterproof paint or primer to get a few more years out of it before starting all over with the right ply.

Any suggestions for a waterproof coating? I was thinking Drylok but it only list masonay for its use. Didn't know if I put this on ply am I just going to exacerbate the problem?

Drylok is not the right (post #200536, reply #1 of 9)

Drylok is not the right thing.  At a minimum you want a heavy enamel paint.  An epoxy paint might be better, but is spendy.  A visit to a real paint store might be the best approach to picking a product.

Pay particular attention to sealing edges and seams, where water will get in first to cause the delamination.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Waterproof paint over plywood (post #200536, reply #2 of 9)

Paint and many deck coatings fail when used on a flat or low slope surfaces without recoating as often as every three years.  The wood expands and contracts daily working the paint.  UV breaks the paint down. The seams and metal edge details show the most movement,  metal due the different coefficient of expansion and contraction and seams , well because they are seams and each piece of plywood grows and shrinks daily. Failure is inevitable, As the wood expands and contracts, it can surface check the aging coating.  Your basic protection with paint is multilayer, and elastomerics.  Here again urethane not acrylic for ultimate elasticity.  Coating every 3 years or so.  When moisture is allowed under, around or through the paint or coating bonding becomes problematic or futile.  Treaded plywood is never the answer, and I mean never.  I like to suggest building the deck following duradek's "plywood recommendations" without the use of treated lumbers for trusses are not treated,  nor should your joists be treated(unless less than 18 inch off the ground a building code requirement).  Then call in a professional PVC deck membrane company with factory trained installers.  Verify the installation company with the manufacturer.  Have him protect and warrant your investment  because in waterproofing a do it yourself install is a warrant it yourself  and if it fails it is your fault.  Don't blame the plywood.


Of course, the OP didn't say (post #200536, reply #3 of 9)

Of course, the OP didn't say whether this was a horizontal or vertical surface or what.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Of course, the OP didn't say (post #200536, reply #6 of 9)

Your are right he did not, but it was in the question. I metioned ureathan, not a d******k (midldle name) product.  It is just being int he waterproofing prossion the question is common.

My appologies Dan.


following duradek's (post #200536, reply #4 of 9)

Not much of what you wrote has anything to do with the posters question.

And it seems Duradek is your middle name.

Are you just trying to insert the name of the product into the discussion ?

or perhaps I misinterpret your reply.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


Little more info (post #200536, reply #5 of 9)

Given some resposes I see now I should have provided a little more info. 

We're talking an outdoor patio item that was originally painted. Held up well for a couple summers but when a few cracks on the edges showed, it was down hill from there. And your right I can't blame the plywood, I blame myself for using the wrong stuff. You see I wanted a fairly smooth finish after it was painted but I was too cheap for any of the good stuff so I used inexpensive 3/4 Luan. Not the stupidest thing I've ever done but I should have known better because I know Luan delaminates if you just think about getting it  wet. :-)

P.S. Were talking all angles horz, vert. etc. It's the undersides where the sun don't shine that took the worst of it.

You're still being a little (post #200536, reply #7 of 9)

You're still being a little mysterious with "patio item".  I'm guessing this some sort of sculpture, or perhaps furniture with a sculptural twist?

But if you say it's the undersides that fare the worst, likely ventilation is more important than the coating on the plywood -- see if you can't invent ways to get a little more air flowing in the nether regions.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

You're on the wrong track- (post #200536, reply #8 of 9)

You're on the wrong track- especially if this stuff is already showing signs of weathering.

Preparation is critical. "Break" the edges, fill all gaps with putty- no matter how small. Where the edges are begining to fray, saturate them with a diluted wood glue, cover with saran wrap, and clamp until set. If there are areas where water pools, drill a 3/16" weep hole.

"Prime" with a thin, penetrating coat to seal. Shellac, Kilz, Spar Urethane, or an oil-based primer are all good choices. If the surface dries shiny, buff it with a scotch-brite pad before painting.

Finally, apply your 'finish' coat, using an exterior paint. Forget any 'epoxy,' Epoxy and sunlight don't mix.

It would take a few paragraphs to explain (post #200536, reply #9 of 9)

DanH, it would take a few paragraphs to explain this "item", lets just call it a storage box that hangs. It is top side is protected with a small but seperate roof. I'm not sure if the horizontal undersides took a major beating becasue how water drips off the sides or the way it was stored one winter, not by me, sitting right on cold damp cement.

renosteinke, thanks for the input. Have begun already what you suggested. Gluing and clamping down any loose layers, sanding off any lifted paint and filling cracks etc with putty.  Will use Zinsser B-I-N that I already have on hand.