How do you keep plywood from warping in high humidity?

[maggiethecat]

Was looking at the Raabe retreat cabin (10x14) and saw they made their door out of plywood. From my reading about building in Hawaii the humidity in that area is always around 100% and causes plywood to warp. How would I seal the plywood door to keep it from warping?

A couple I read about had issues with that in their house in Eden Roc on the Big Island.

http://moonoverhawaii.blogspot.com/2008_01_01_archive.html


--maggie

[glenn kangiser]

As the wood will likely have a high moisture content when you seal it, about the only product that I can think of that would let moisture out but not back in is Defy from Saver Systems I think.   It also has special resins that are mold resistant.

http://aloghomestore.com/finish-defy.shtml#defy-original

[Redoverfarm]

Maggie you don't have to live on the islands to see the effect of warping in plywood.  It is a wonderful product but it's like everything else and has it's draw backs.  That is why in it's application has to be supported, attached well and sealed.  Most of all doors made now have plywood and very few are made of solid wood.  But as glenn pointed out sealing it is the most important when exposing it to elements. 

Another point is that the thicker the sheet the less chance of warping.  A well made frame also reduces the process and holds the shape.

[peternap]

Maggie, as John and Glenn pointed out, it will warp on it's own. It is fairly dimensionally stable however. The warp doesn't change the size, just the shape. We are obsessed with the idea of "Sealing" these days and with something like a door, a complete seal is not impossible.

Carpenters have been dealing with the problem since the beginning of time. Loose fitting raised panels for interior doors, were used to eliminate size changes, for example.

I don't like trying to seal anything because the wood needs to breathe. I've not tried the product Glenn referred to but it's the right idea. John has the right idea though. Proper framing of the door, with the crowns properly orientated (out) and proper joints will minimize or eliminate the warping.

For a finish, I'd use one of the traditional oils that do allow breathing. If it is to be painted and I can't think of any other way to make it look like anything other than plywood, I'd use linseed oil as a base.

There are also local options (wookie wookie oil or something and you should check to see what the locals are doing.

There are also lots of different types of plywood. If you used marine grade plywood for example, no "sealing is necessary" just paint or stain it. Luan, also know as doorskins, is Rosewood and comes in exterior as well as interior grade. I used it to build sea kayaks. It can be laminated onto exterior grade plywood for an exterior door or affixed to a frame alone for an interior door.

[John_C]

I think the ambient humidity would be less of a problem than the intermittent heavy rain and strong sun... a killer combination.

I would be inclined to get enough sheathing and bracing on it to allow the roof to go on ASAP.  Those large overhangs will do more to protect the sheathing, siding and subfloor than any goo you could put on the wood.  If you used OSB on the corners it wouldn't be that big a deal financially if you had to replace some of it.

[MountainDon]

I solved the door problem by going steel.