The most common use for drywall joint compound, or "mud," is to fill the joints between installed drywall panels to create smooth, flat walls. Not only is the mud valuable as a filler, it is a bonding agent that adheres to nearly any porous surface. In some commercial applications, builders install plywood walls and then skim-coat the wood panels with drywall mud for a Southwestern stucco look or for hand-troweled Old World appeal. You can do the same thing at home.
Acceptable Types of Wood
You can apply drywall mud to any rough-grain wood surface. Plywood or oriented strand board (OSB) are good choices, but the mud will also stick to painted wood, as long as the paint is flat and not glossy. Drywall mud is not intended for outdoor use, so don't skim-coat a garden shed. By the same token, do not apply the mud to wood that will come into direct contact with water indoors, such as a kitchen backsplash or a plywood bathtub surround.
Drywall mud comes in dry and premixed products, with the premixed mud being more expensive, but much easier to apply. You can apply the mud by hand with a trowel as craftsmen once applied plaster to cover wood laths to form walls, but the quickest way is to thin the mud and roll it on with a paint roller. If you don't want the wood beneath to show through, you'll have to roll on two or more thin coats of mud, letting the first coat dry completely before rolling on the second coat.
Creating Texture Designs
Drywall mud offers infinite design potential. Once the base coat dries and you sand off the rough spots with a drywall sander, you can add texture to the surface. This requires another coat of mud. While the mud is still wet, you can smack it with a slap brush to create a stippled effect or use a putty knife to create a swirled pattern. If you roll the texture coat on thickly, you can wait until the bumpy surface begins to dry and then lightly pull a trowel over just the tips of the texture to make a "knockdown" effect. Practice your design technique on a scrap of plywood before applying it to a large area.
Wood moves more than drywall does because it can swell in high humidity or contract as it dries. Joints between wood panels should be taped just like joints between drywall panels to reduce the risk of cracking in the seams. If the wood does move, it's likely that cracks will appear in the surface of the dried compound.