Wall repair first step to a good paint job

With spring in the air, don't be surprised if you feel like doing some interior painting. It's all part of how we Canadians shake off cabin fever. And now that you can open the windows and let some fresh air in, there's no better time to roll on a new, clean coat of colour.

A really good paint job, however, requires more than just a roller and tray, a can of latex and some patience. You've got to start by making a smooth foundation for your work first, and this means filling all the dents and dings in your walls before you get going. Here's how.

Homeowner's Wall Repair Kit

Whether you've got walls covered in plaster or drywall, the ideal repair tools and techniques remain the same. You'll need a small tub of ready-mixed drywall compound, a 4-inch wide drywall knife, an abrasive sanding sponge and, if you've got some major repair work ahead of you, a small bag of setting-type drywall compound. More on this later. You can get all the basics for less than $30.

Fixing Small Dents, Scratches and Old Picture-Hanging Holes

This is the kind of damage you'll be fixing most often, but luckily it's also the easiest to do well. The main trick is to dimple the surface of any area of damage that has frazzled edges. Every old nail or screw hole fits into this category, as do major puncture wounds. If you leave the frazzles level with the surface of the wall, they'll stick up through your repair job and look terrible. To avoid this, pound the frazzled area with moderate blows from the rounded, butt end of your putty knife, or a screwdriver handle. Aim for a depression that's about 1/8-inch below the surface of the wall at its centre.

The next step is to apply a smooth skiff of drywall compound into and over the damaged-and-dimpled areas, using the blade of your putty knife. For best results the compound must be thoroughly stirred first. Lumps are no good. Professional drywall artists use compound by the gallon and stir each pailful before use with a metal beater driven in an electric drilling to ensure smoothness. You can achieve the same degree of mixing in your small tub by using a 1 1/2-inch diameter spade bit as your beater. Chuck it into a variable speed drill and spin slowly, then wash it clean with water.

If you've spread compound successfully, you should end up with a bit of excess extending beyond the edges of the repair zone, and some slightly above the surface of the wall. Now wait for it to dry. This'll take 8 to 24 hours, depending on room temperature and humidity. Fully-dry compound readily forms dust when sanded with your abrasive sponge block; still-wet compound will be gummy. Don't rush things or you'll make a mess. If your repair area is deep enough, you may notice that shrinkage of the first coat of drywall compound has created a hollow that's still visible after sanding. If so, swipe on another skiff of compound, let it dry, then re-sand. Two coats should do the trick for minor repairs.

Fixing Holes Bigger than a Marble, Smaller than an Egg

The main challenge in fixing anything larger than a nail hole is the tendency for ordinary drywall compound to shrink as it dries. In fact it can take days for a thick blob of compound to dry, and when it finally does it's usually cracked. A faster, stronger alternative is to use a repair compound that hardens by chemical reaction, not evaporation, like ready-mixed drywall compound does. This type is called "setting-type" compound and it doesn't shrink at all as it cures. The fastest formulations are also rock-hard less than two hours after application. Setting-type compounds always come as powder that you mix with water into a buttery paste just before application. They're available from any building supply outlet and better hardware stores. Since this product is intended for professional use, it usually (though not always) comes in large bags. Don't let this discourage you. Even in bulk, this stuff isn't expensive and it'll keep for years in a dry spot. Some versions are so tough after curing that sanding is impossible. One sandable version I like is Sheetrock 90. For maximum strength use a non-sandable product like Durabond 90; just be sure to trowel it slightly below the surface of the wall before you leave for a coffee break. Follow up with a thin, sandable skiff of ordinary drywall compound later.

Fixing Holes Bigger than an Egg

Holes bigger than about 1 to 1 1/2-inches in diameter should always be filled with a setting-type compound. They also require some kind of physical backing to support the compound as it's applied. Without backing, the compound would simply slump down or fall into the wall cavity before it sets. The best kind of backing surface is made of strips of 1/2-inch thick plywood, cut to about half the width the of the crater you're filling. Cut several pieces about 2 inches longer than the span of the hole, then snake them into the wall cavity and fasten them there using drywall screws driven just below the wall surface. A temporary screw in the centre of each backing slat creates a good handle that can be removed after the slats are secured along the edges. Leave a 1/8 to 1/4-inch gap between each slat so the compound will have something to root into.

A 4-inch wide drywall knife is the best tool for spreading the first coat of setting-type compound over the backing slats. Let it cure, then top-up with one or two coats of ready-mixed drywall compound, sanding between each coat. When you're done, there should be no visible ridges where the repair stops and the old wall starts. This "feathering" effect is achieved when you've sanded the edges of any wall repair successfully.