Do I Have to Use Felt Paper on a Retaining Wall When Applying Stone Veneer?

Moisture Barrier

• A moisture barrier is either a sheet of plastic or a tar-based felt paper that is installed beneath the veneer itself but on top of the retaining wall. All veneer walls will eventually wick moisture, which means the moisture will eventually make its way through the stones and the grout joints between the stones, and the moisture barrier acts as a trap that keeps moisture from affecting the actual retaining wall itself.

Concrete Walls

• One of the natural aspects of concrete is that it breathes. This means it inhales and exhales just like a human body, plus it takes in and expels moisture. If a moisture barrier is used on top of the concrete, it will actually trap the moisture against the surface of the concrete, rather than allowing it to evaporate naturally as it would if there were not a moisture barrier in place.

Wood Walls

• Any type of wood installation will need a felt paper moisture barrier installed between the chicken wire or wire mesh and the wood itself. This moisture barrier helps the moisture that will eventually wick through the veneers from ever reaching the wood beneath the paper. If moisture penetrates, it will eventually rot the wood out, leading to your retaining wall breaking down and eventually falling apart.

Interior Versus Exterior

• Felt paper over concrete retaining walls isn’t needed. This is because stone veneers are installed on top of the concrete retaining wall’s surface with thinset mortar, which is cementitious in nature. This means it contains cement, just as concrete does. The grout that goes between the veneers is also cementitious, which means everything will breathe normally and evaporate the water. Plus, concrete isn’t damaged by moisture, so a moisture barrier isn’t necessary.