Cultured stone, also called manufactured stone, has a lot in common with natural stone in terms of beauty and elegance but offers a number of distinct advantages as well, including the fact that cultured stone is less expensive and lighter than natural stone, making it an ideal choice for many homeowners who prefer to do the installation themselves. However, the cultured stone can only be installed on certain surfaces, and drywall does not serve as a proper base for this material.
Problems With Drywall
While it is a reliable building material, drywall is not waterproof or water resistant, which limits the materials that can be applied directly over the surface. When you install cultured stone, you will use mortar or thinset to hold the pieces in place. These adhesives are similar to cement in that they are mixed with water to create the proper consistency. If the adhesive is applied directly to drywall, the paper facing of drywall will absorb the moisture from the adhesive. The moisture will crumple the drywall from the inside out, and the entire installation will fail.
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If your application area is made of drywall, you can cover the drywall with materials that will support the moisture-based adhesive. Cover the wall with a water-resistant barrier, such as building paper or roofing felt. Run the barrier horizontally across the surface, and overlap seams 6 inches between rolls as necessary. Attach the material to the studs in the drywall with galvanized nails or staples to prevent rusting. This material will prevent moisture from the adhesive from leaking into the drywall and rotting it away. Once the water-resistant barrier is in place, attach 2 1/2 lb. diamond mesh metal lath using the same galvanized fasteners. The lath will support a base wall for the cultured stone application.
Base Coat Application
The lath is full of holes that you must fill in to ensure a solid, flat cultured stone application. Spread a 1/2-inch thick coat of mortar over the entire lath surface, filling in all holes or cups in the lath. Completely flatten the mortar coat so that the cultured stone will sit flat against the surface when it is finally installed. This base coat should dry for at least 48 hours before you install the individual stones to ensure that the adhesive from the stones has a stable and secure base to which it can bond.
If you have not installed the drywall yet, or if you have the ability to replace the drywall, there are a number of other materials you can use. Cement backerboard, also called gypsum board, is essentially a waterproof version of drywall. It is installed in the same way as drywall but features a solid core that does not crumple if it comes into contact with moisture. This support structure would need only the lath and base coat to support the cultured stone; it is its own waterproof barrier.