Preparing for Plaster Walls: Plywood and T&G Wood

The interest in plaster walls is high as more people fall in love with it's inherent beauty and as we learn about the indoor air quality benefits of natural finishes on our walls. I get more and more people asking me to install plaster and if the surface we are wanting to cover is wood or plywood, there's a lot more involved.

Plaster actually works wonderfully over a wood wall, however there is a lot more that goes into preparing the wall for plaster which increases the time and materials needed for a successful installation. This in turn means a more costly install. For those of us that are plastering over wood here we go.

Plywood: Even though more stable than solid wood, plywood, likes to move with changes in temperature and humidity. If you have had a hardwood floor, you may notice the cracks between boards can get larger and smaller depending on the season, that is the air moisture content affecting the wood. Plaster on the other hand, does not like to move, it's stone or clay, and while lime and clay plasters have some flexibility, they cannot keep up with the movement of wood. So how do we plaster over plywood?

In short, we separate it from the plaster.

1. Hang two ply tar paper by stapling it to the plywood. This can be found at most masonry supply stores. Austin Masonry Supply

2. Use lath screws to hang metal lath over the tar paper. The lath should be solid and not move much if at all. Usually a screw every 6-10 inches does it.

   

   Metal lath going over the two ply tar paper.

3. Use the appropriate brown coat material over the lath. I like Lift by New Age Artisans.

   Plaster for Lath It takes two coats, maybe three be sure to level it out.

4. Scratch or prep coat can be applied over this.

5. Your finish coats go up.

New Age Artisans Lift, a scratch coat going over lath.

As you can see, there are many more steps and a lot more material to go over plywood. Expect the project to cost more accordingly. When done right, you end up with a beautiful plaster finish, measuring between 3/8" and 1/2" thick. Be sure to plan for the added thickness.

Tongue and Groove Wood: If you have tongue and groove wood on the walls you want to follow the sampe steps as plywood above.

Smooth Venetian style plaster over plywood built out vent hood.