Finishing Plywood for Outdoor Use

[Daniel Smith]

I'm getting ready to help my neighbor build a couple of relatively large speaker cabinets that will spend half the year in his screened deck. While the cabinets won't be directly exposed to rain, they will be sitting in high humidity when it rains and during the dog days of summer. Since we're going to be using plywood for the construction, I'm concerned about delamination under these conditions. Is there a way of finishing "standard" plywood so there's a reasonable chance of the cabinets holding up or do we need to think about using marine ply instead?

Thanks,

Dan

[Scott Holmes]

Marine ply or use "Finnish Birch" plywood same as "Baltic birch" plywood but it has exterior glues.

[Phil Phelps]

Check the lumber yard for Medium Density Overlay. MDO is used for highway signs and you don't see them delaminating. It is covered with a phenolic that holds exterior paint very well. It is available in many thicknesses. If you have a sign supply in your area, check with them for some exterior substrates.

[Howard Acheson]

Be sure to use an exterior rated plywood. Most decorative, hardwood plywood is constructed with interior rated adhesives.

Given the use, I would use an oil based enamel paint as a finish.

[Phil Phelps]

Be sure to use an exterior rated plywood. Most decorative, hardwood plywood is constructed with interior rated adheasives.

Given the use, I would use an oil based enamel paint as a finish.

Howie, as much of an oil base primer guy as I am, I don't like exterior oil paint. It tends to chalk.

[Howard Acheson]

I'm not talking about an exterior house paint. I recommend an oil based enamel paint. It can be used indoors or outdoors.

BTW, exterior house paint is designed to chalk. That's how it is "self cleaning".

[Tony Bilello]

In wooden boat building there is a term "fully encapsulated". This is when eveything is made 100% waterproof. Every sheet of plywood is coated with a layer of epoxy on both sides and all edges. This makes the sheet waterproof. A bit over-kill for speakers though. I would use MDO if they were mine.

[Daniel Smith]

Thanks for all the replies. I was unaware of MDO, so I've learned something from this post. As for the enamel, are there any common brands that I should stay away from or are particularly favored?

[Phil Phelps]

Stay away from home centers and visit a real paint store. Many more options, and better paint, there.