The climate in the garage isn't the same as it is in your house, and your garage walls sustain abuse you would never inflict on your living room walls. These are two reasons why you need a tougher grade of paint in the garage, and you may lose a little in finesse for the gain in durability. Garage walls might be finished with masonry, wood or vinyl paneling, or drywall -- the wall covering material also affects your choice of paint.
Oil or Latex
Because of the volatile solvents it contains, many states limit the use of oil-based paint in the house, but an exterior alkyd enamel may be a good choice for the garage walls thanks to its durability and smooth patina. There's no overarching reason to avoid latex paint, however, because modern formulations are just as durable and glossy. If the walls already have a coat of oil-based paint, though, it's best to stick with the same type of paint to avoid the time-consuming process of scuffing the old paint with sandpaper and etching it with a trisodium phosphate solution -- which would be necessary to get latex paint to adhere well.
Flat, Semigloss or Gloss
The garage isn't the place for a flat finish. Flat paint is easy to scuff, and scuff marks are difficult to wash out of a flat finish. Moreover, garage interiors tend to be moldy, and washing mold from a flat finish can cause permanent discoloration. If you choose a semigloss or -- even better -- a gloss finish for the garage walls, you'll be able to wash away mildew and scuff marks left by tools using soap and water.
Interior or Exterior
Even though exterior paint is formulated for outdoor use, there's a lot to be said for using an exterior wall paint for the interior walls of your garage. Exterior paint is formulated with stronger binders; it's more resistant to moisture than interior paint and it often contains a mildewcide. All of these are desirable qualities in a utility space like the garage, which is more susceptible to high humidity and condensation than your house. That being said, you may prefer an interior wall paint if your garage doubles as a recreation or living space.
Considering Wall Coverings
- Drywall: When drywall is used in a garage, the installers seldom finish it to the same level they do interior walls. They may give it a level 2 or 3 finish, or they may leave it unfinished. Before painting unpainted drywall in any condition, it's important to prime it with PVA primer, which seals the paper and allows the top coat to bind. After priming, you can apply any type of paint, oil-based or latex.
- Wood paneling: Raw wood paneling also requires a primer, but instead of drywall primer, use a shellac-based wood primer. This type of primer not only seals the wood, it prevents tannins from bleeding through the top coat. If the paneling is already finished, clean the finish with TSP and water, and scuff it with sandpaper before painting. Use a primer if the old finish is cracked or peeling. You can apply any type of paint to primed or properly prepared prefinished wood paneling.
- Masonry: Cement and brick walls are subject to moisture seepage from outside and need a special sealer to block that moisture. After the sealer dries, apply concrete primer and masonry paint, which is an elastomeric coating that also waterproofs. Although it's a bit more difficult to handle, you can also give the walls excellent protection by using epoxy enamel. Apply sealer, primer and paint with a brush or roller.