Quote Originally Posted by ordjen View Post

On plywood surfaces I prefer acrylic porch and deck paints. Oil paints form a ridgid film which becomes more ridgid and brittle with age. Aging plywood often exhibits the wood grain opening up. The oil paint has no elasticity resulting in the paint film splitting openwith the grain.

Were I painting such a structure, I would first prime the plywood with an oil primer to set the grain. After a light sanding, I would give two or three coats of a quality acrylic porch and floor paint. It would also be a good idea to mix in a little traction sand to keep people with wet feet from slipping.

For a similar reason, I tend to favor acrylic floor paints on tongue and groove porch floors. T&G also swells and contracts with the seasons, making every seam vulnerable to water entry. Acrylic floor paint has a greater chance of being able to flex with the wood movement, maintaining tight seams. Even if water should gain entrance, acrylic breathes better than oil paint, giving the moisture a chance to exit without causing the paint film to pop.

The lower sheen of most acrylic porch and floor paints is also far less treasurous when wet than the slick, higher gloss oil paint.
Thank you -- so 100% acrylic -- which I believe is water based latex -- is your preferred choice. For the reasons you noted, and simpler cleanup, I think I'll be hard pressed to ever use oil again.

On the pontoon, the ply was very open grained. It had weathered for a year. It was very rough, but mostly un-sandable because of the remaining glue from the carpet. It would gum-up my sander. I did hit it with 40 grit. I rolled-on about 3/4 gal of the Valspar urethane oil -- http://www.lowes.com/pd_48233-4-009....rch&facetInfo= -- thinned with mineral spirits for the first coat. Then I brushed on an un-thinned second coat. It's still a little rubbery, but it does not have a solid uniform appearance. It looks like another coat is needed, but I may just let this wear a season and next spring apply the acrylic latex. I was going to mix in some sand on the second coat, but the surface is so rough already, I let it be. In fact, I need to sand down / tear-out a few sliver potentials.

On my porch -- should I prime/paint all sides of the untreated t&g boards before installing? New boards will all be PT, so I plan to install - let it rest a few months - and then paint. I also heard it might be good to paint the tongues while installing. I may have a mixture of re-useable boards and new PT ones.