Before anything, we'll quickly note that we are making a distinction between interior and exterior stone veneer. Exterior applications require additional enhancements like flashing and water-impermeable membranes, on account of the weather. If you are only veneering an interior wall, you do not have to deal with these considerations. On the inside, it's mainly about aesthetics.
In short: Yes, you can veneer over brick. But like any surface, the brick must be prepared correctly. In general, you will encounter both painted and unpainted brick:
Painted Brick: Forget about applying a scratch coat to the brick. Painted brick will not "take" the scratch coat.
Unpainted Brick: Unpainted brick isn't necessarily perfect for the scratch coat, either. Smooth-surfaced brick or very crumbly brick still are not appropriate for a scratch coat. In the first instance, the brick is not porous enough to accept the mortar. In the second instance, mortar will not stick well to the brick because the brick surface itself is failing.
Regarding surface treatment, you have three options. With the first option, you attempt to deal with the brick itself. With the second and best option, you forgo the brick entirely, essentially creating a "new" surface out of metal lath.
- Prepare Brick Surface: Sand or waterblast paint, dirt, or oils so that you have a raw, fresh, porous (but not crumbling) surface. Some masons claim that this is an adequate surface for accepting a scratch coat.
- Install Metal Lath: Metal lath is the best surface you can apply prior to the stone. Apply corrosion-free 18 gauge metal lath to the brick with masonry fasteners. Make sure that the "cups" of the lath are pointing upward (think of the abrasive surface of a cheese grater). Overlap both the horizontal and vertical seams by one inch. Be sure to wrap the lath around corners (both inside and outside) rather than applying two separate pieces of lath.
Which Type of Stone Veneer to Use?You have three choices: natural stone, cultured stone, or faux stone.
Natural stone is the real thing: carved from the Earth, beautiful, heavy, and difficult to work with. However, natural stone can be workable when cut into a thin veneer. This makes the stone lighter and easier to handle.
Faux stone has no stone products in it at all. It is a high-density polyurethane and usually comes in panels, rather than individual "stones," for quicker installation. Many faux stone products are cast in the shapes of real stones, so they are quite realistic. The similarity ends when you rap on faux stone with your knuckles; it feels hollow and fake.
Made from Portland cement, aggregates and iron oxide pigments, cultured stone or artificial stone are names given to an artificial stone veneer that looks much like real stone ("Cultured Stone" is also a trademark of Boral Stone Products LLC).
Artificial stone is heavier and more substantial than the polymer faux panels, but not as heavy as real stone. It comes in individual "stones" that you fit together piece by piece and mortar into the wall, just like real stone. According to Cultured Stone, diameters range from 2" - 30" and have an average wall thickness of 1 3/4".
The Masonry Veneer Manufacturers Association has an excellent set of installation guidelines, Installation Guidelines for Adhered Concrete Masonry Veneer, that I recommend you check out.