Because bathrooms generate the most moisture in a home, these walls must be constructed differently from the others. Most importantly, they must be water-resistant to prevent moisture vapor from migrating through the walls. Walls surrounding a bath and shower must be completely waterproof. This is accomplished by using different types of wall underlayment.

Remodeling or New Construction

If remodeling or building a new bathroom, the bare stud walls should first be covered with water-resistant drywall. If you are stripping off old wallpaper or ceramic tile, it's worth your time and money to remove any wallboard that is not water-resistant. You can identify water-resistant wallboard by its light green color.

Wallboard around a shower or bathtub must not only be water-resistant but must have added protection to prevent any water intrusion, which can rot wood subfloors and stud walls. After the wallboard is up, the walls are covered with waterproof cement board, which is fiberglass-reinforced mortar. The joints are sealed with epoxy, and then the finish layer, such as ceramic or stone tile, is applied.

When covering a wall behind a bathtub with ceramic tile in new construction, tile all the way to the floor to protect the substrate from water damage that may occur over the years. If it is not possible to move an existing tub, the joint between tub and tile must be carefully caulked.

DryWall

Drywall is ideal for any number of finishes, including paint, wallpaper and textured, for areas other than the tub or shower. In all cases, it first needs to be taped and sanded, which involves covering the joints with tape and joint compound, resulting in a smoothly surfaced wall.

Another common drywall finish is a smooth or textured coat of drywall "mud" coat. Smooth finish is preferred in bathrooms for ease of cleaning. A smooth finished wall, which also requires priming and painting, is different than just having the wall taped and then painted. The labor-intensive smooth finish, which requires an experienced pro to accomplish, means applying several coats of drywall compound and finishing it so the wall is flawlessly smooth. Looking at the wall while a bright light is shined along it from the opposite end is the quality check.

Painting

When painting, start with a primer and then the finish coat. Paint falls into two primary categories, latex or oil-based.

• Latex is water-based, which means it is quick-drying, nearly odor-free and cleans up with just soap and water. It is more flexible and more resistant to sun fading than oil-based paints. And particularly important for bathroom use, latex paints contain additives to resist mold and mildew. However, if applied over wallpaper, it tends to soak the paper off the wall; if applied over bare wood, the water causes the wood to swell and warp. Also, latex will not bond well to oil-based paints, particularly those with a glossy surface. In such cases, first apply an oil-based primer, then the latex.
• Alkyd paint, which has largely replaced oil-based paints, is much more durable. Alkyd is a synthetic resin. It is quite odor-free and dries in four to six hours. It can be painted over wallpaper, but should not be applied directly to wallboard because it raises a nap on the paper covering after it dries. Always use a primer first.

• High-gloss paint, which is the most moisture resistant because of the high resin content. Higher resin paints are also more wear resistant, which makes them ideal for areas that must be wiped often.
• Semigloss paints are also durable, but have less of the reflective glare that accompanies high gloss paint.
• Satin sheen, a compromise between semi-gloss and flat paint.
• Flat paints do not produce any glare, but are not as durable as the higher gloss paints.

Wallpapering

Wallpapering bathrooms is no different than covering other walls, but using smooth-finished wallpaper makes it easier to wipe down. The drywall under it must be primed or sized first.

Other wall coverings include cast polymers in slab form that are finished in a variety of patterns, including marble, granite or solid colors. Marble or granite tiles are also popular choices for walls because of their beauty and easy maintenance.