General Interior Surface Prep

As with exterior projects, it is very important that you take time to properly prepare any interior surface that you want to paint. This will help ensure that the finished paint job will look smooth and uniform, and that it will last a long time.

For interior painting, good surface preparation requires that you thoroughly clean – and, if necessary, repair – those surfaces that will be painted. These simple steps are essential to get professional-looking results.

Cleaning Interior Surfaces

Whether you are painting walls, ceilings, or trim, the starting point for any interior painting project is to clean the surface you are about to paint. Remove accumulated dust, dirt and grime by scrubbing surfaces with a sponge and mild household detergent solution.

If stubborn stains are present – for example, oil, grease, or mildew – clean the surface using a scrub brush and a stronger cleaning solution containing ammonia or household bleach. Ammonia should be mixed with an equal amount of water; bleach solutions, which are particularly effective in removing mildew, should contain one part bleach to three parts water. When using either of these cleaning solutions, be sure to wear rubber gloves and safety glasses. Do not mix ammonia and bleach together; doing so will produce noxious fumes and could result in serious injury.

After cleaning, rinse off the interior surfaces and allow them to dry completely before applying any type of primer or paint.

Making Repairs

If your walls are like most, they will need some minor repairs before painting. The same is true of ceilings and trim.

Start by making a careful inspection of the surfaces you will be painting. If you are painting large areas or several rooms, it is wise to take notes as you go along. Look for cracks, gouges, and holes; open or uneven joints in woodwork; and cracked, chipped or peeling paint.

Filling Cracks and Seams

You can quickly remedy cracks or seams in plaster and wallboard with caulk, drywall compound, or spackling paste. If you use caulk, choose a top quality, water-based all-acrylic or siliconized acrylic caulk: This type of caulk is easy to use, eliminates the need for sanding, and can be painted with a top quality paint less than an hour after application. (Certain caulks, such as silicone caulk, cannot be painted at all.)

If the crack or seam was previously caulked, remove as much of the old sealant as possible. If loose paint is present, scrape it off, then sand the area and dust it off afterwards. Surfaces adjacent to cracks and joints should be clean, dry and dust-free when caulk is applied. When caulking cracks or joints that are deeper than ½”(1.27cm), fill the gap with a foam backer rod before applying the caulk. If the gap is not that deep, a backer rod is not necessary.

Apply the caulk with a caulk gun, working the trigger to keep constant, but not excessive, pressure on the material. Before the water-based caulk dries, smooth it out by running a moist finger along the crack or joint. But be careful that you do not remove too much caulk during this tooling process; the material will naturally shrink a little as the water in the caulk evaporates. (Note: Caulk should not be sanded.) A second application of caulk may be needed to obtain a uniform, flush surface.

Follow these same procedures to seal other gaps for example, where baseboards, chair rails, crown molding and trim meet your walls and ceilings. Likewise, caulk is excellent for closing gaps in mitered joints.

If you do not have caulk, then use drywall compound or spackling paste to fill cracks, gaps, joints and small gouges. Before applying either of these products to wails and even woodwork, scratch or score the edges of the area with a putty knife to create a more “grippable” surface, then brush off any dust that is present. Apply the material and feather it out until it is flush with the surrounding surface. After the material dries, sand it to a smooth finish.

Repairing Holes in Plaster

To repair large holes in plaster, brush or scrape away any loose plaster that is present around the hole (or between the strips, if laths have been used). Next, undercut the edges of the hole with a special widening tool or an old-fashioned can opener – this will help keep the new plaster in place.

If wood laths or gypsum laths are missing, take a wad of paper and pack it into the hole as tightly as possible. Dampen the area with water.

Using a broad putty knife, press a small amount of replacement plaster firmly against the edges of the hole and pack it tightly against the lath. Try to fill the hole to about 1/4″ to 1/8″, or 5mm, below the wall surface. Allow the plaster patch to dry until it becomes slightly tacky, then score it with the edge of the putty knife. Allow the plaster to dry completely. Repeat the process again. However, this time, apply enough plaster so that the patch is level with the surrounding wall surface. Wait for it to dry. Then sand the patch to the level of the wall. Dust off the area and apply a latex or oil-based sealer.

Repairing Small Holes in Plaster Wallboard

While it is a simple matter to repair surface gouges in wallboard with caulk, wallboard compound or spackling paste, holes present a bigger challenge, since there is typically no backing behind wallboard. If you need to repair small (1″ to 2″ / 2.5cm to 5cm) holes in your wallboard, do the following:

    1. first, clean loose material away from the edges of the hole
    2. next, cut a piece of firm cardboard that is slightly larger than the hole
    3. insert a strong piece of string through the cardboard, and knot it so that it cannot be pulled through
    4. push the cardboard through the hole and pull it tight so that it provides a “backing” for the hole
    5. while holding the string firmly, liberally apply fast-drying patching compound to the hole (allow it to seep between the back of the wall and the cardboard); apply enough patching compound so that the material fills the hole just below the front surface of the wallboard
    6.  when the patch dries, release the string and cut it as close as possible to the wall
    7.  score the surface of the patch by scratching with the edge of a putty knife
    8.  apply a second layer of patch and smooth it out with a broad putty knife
    9.  sand to the level of the wallboard

Repairing Large Holes in Plaster Wallboard

Large holes in wallboard (3″ / 7.6cm or more in diameter) should be patched with either a spare piece of wallboard or a commercial patching kit.

If you have a piece of wallboard available, use a jigsaw to enlarge the hole by cutting outward to the studs on either side. Size a piece of wallboard to cover the hole and nail it to the studs. Apply drywall compound to the seams; after the material dries, sand it flush to the wall surface.

Alternatively, if you use a commercial patching kit, follow the instructions on the label.

In either case, keep in mind that the patching material may be more porous, than the wallboard, which could create an uneven appearance when painted. For this reason, it is important to apply a sealer at least over the repaired area before applying the paint. For best results, apply the sealer to the entire wall.

Dealing with Cracked, Chipped, or Peeling Paint

If you have any cracked, chipped, or peeling paint, this must be removed before you apply any type of coating. Check your woodwork and trim carefully: These problems are common in such areas.

Use a scraper to remove as much of the loose or peeling paint as possible. Next, sandpaper the surface to feather the edges of any remaining paint to a smooth finish. If any bare wood is exposed, spot-prime with an acrylic latex interior primer.

Caution: If you suspect the presence of old paint containing lead, do not sand the area. Contact your paint retailer for instructions on how to proceed.

Painting Over Wall Coverings

While it is usually best to remove wallcoverings prior to painting, if the wallcovering is in good condition (no severe blistering or bubbling, etc.), it is usually possible to paint right over it with excellent results. This is true even if the wallcovering has minor imperfections.

The first step is to correct any small problems that exist. For example, if there are small bubbles in the wallcovering, slit them with a razor, glue them down and press them flat with a seam roller.

If the wallcovering is torn away in spots, flake off any peeling edges with a putty knife, feather in spackling compound, then sand to a smooth finish.

Always use a primer before painting over a wallcovering. A stain-blocking primer is best, since some wallcoverings contain dye that can bleed right through ordinary primers’ and paint.

As a precaution, you should spot-test the primer and apply paint over it before you coat the entire wall. Do this in a concealed area: behind a couch, for example. The test area will show whether the primer has satisfactory stain blocking characteristics for your wallcovering. Check the test area carefully to make sure the wallcovering does not loosen when covered with the primer and paint. Also, make sure the primer goes on evenly without “crawling” – if the primer crawls, you either need to clean the surface, or, possibly, remove the wallcovering.

If, for whatever reason, paint cannot be applied over the wallcovering, you should remove the wallcovering. In some cases, a wallcovering can simply be pulled off of the surface in large sheets. More often, this can be accomplished by applying a chemical wallpaper stripper to soften the wallpaper, so that it can be quickly and easily scraped off the wall. If the wallcovering proves especially difficult to remove, try scratching the surface with a special scoring tool or heavy grit sandpaper before applying the chemical stripper. Beyond that, it may be necessary to rent a steam stripper.

Whatever method you use to remove the wallpaper, it is essential that you also remove all of the paste from the walls. This can be accomplished by vigorously scrubbing them down with a trisodium phosphate (TSP) solution or a commercial wallcovering glue remover. Rinse the walls thoroughly. When they are dry, carefully sand the walls with 80 or 100 grit sandpaper, then dust them off.

Final Preparation Steps

Before applying any type of interior coating, take time to do the following:

First, dull any glossy surfaces, whether painted or not, with medium-grit sandpaper. This will give the surfaces “tooth,” so the new coating will adhere better.
Dust off all prepared surfaces a final time.
Cover furniture and floors with drop cloths to protect them from paint spatters and spills.

WARNING! If you scrape, sand or remove old paint from any surface you may release lead dust. LEAD IS TOXIC. EXPOSURE TO LEAD DUST CAN CAUSE SERIOUS ILLNESS SUCH AS BRAIN DAMAGE, ESPECIALLY IN CHILDREN. PREGNANT WOMEN SHOULD ALSO AVOID EXPOSURE. Wear a NIOSH-approved respirator to control lead exposure. Clean up carefully with a HEPA vacuum and wet mop. Before you start, find out how to protect yourself and your family by contacting the National Lead Information Hotline at 1-800-424-LEAD or log on to

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