How to Prepare for House Painting
Repairing and preparing wood for longer-lasting paint.
We'll show you how to prepare your house for painting and make your paint job last longer. Careful prep work on these trouble spots will double the life of your paint.
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Wood close to the ground
If the lower ends of your garage door trim just won’t hold paint, here’s why: Concrete soaks up water, then releases moisture slowly. So any wood next to ground level concrete stays damp, and that constant dampness breaks the wood/paint bond. The same goes for any wood that touches a deck, patio or other surface where water sits.
To correct the problem, create a gap between wood and horizontal surfaces. Then apply paintable water repellent to the bottom 16 in. of the wood. Properly applied repellents add several years to a paint job in areas highly vulnerable to moisture.
Begin by scraping away all the paint in the peeling area. Two or three coats of paint can usually be removed with a combination of paint scrapers and sandpaper (Photos 1 and 2). For heavier buildup, use a heat gun to soften the paint as you scrape. Be careful with a heat gun—it can melt nearby vinyl and weather-stripping.
As you scrape, you may find that the wood has turned gray or black in some areas. Check for rot by probing these areas with a nail. Spots that are discolored but firm are simply weathered. Weathered wood doesn’t hold paint very well, so sand away the gray surface. If you find soft areas, you’ve got rot. Small, shallow soft spots can be dug out and repaired with a two-part, exterior filler such as Minwax High Performance Wood Filler. But when rot is deep and widespread, it’s best to replace the entire piece of wood.
Next, undercut the trim to create a gap (Photo 3). When you’re done, scrape any dirt or gunk out of the gap with a putty knife and blow out the dust using a vacuum or air compressor. To avoid staining the concrete, run at least three layers of masking tape under the wood. Apply repellent to all bare wood (Photo 4) including the underside (Photo 5). Bend a putty knife in a vise to make a handy tool for reaching into tight areas. Remove the tape right after application.
The label on the repellent will tell you how long to wait before applying a primer. Many repellents require an oil-based primer, so be sure to read the label. Then apply two coats of paint (Photo 7).
A single coat of paint may look fine, but two coats form a more durable film that resists moisture better and lasts longer. When using paint and primer, don’t ignore the temperature and humidity ranges listed on the label—weather conditions during application really do affect paint longevity.
If your home was built before 1979, the paint might contain lead, which is extremely hazardous to children age 6 and younger. Call your local public health department for information on how to check for lead and handle lead paint safely. For a free booklet on dealing with lead paint, contact the U.S. Environmental Protection Agency at www.epa.gov/lead.
A board that won’t hold paint
Sometimes a piece of wood siding or trim peels while neighboring boards don’t, even though they all get the same sun and moisture exposure (Photo 1). In a case like this, the board itself is usually the problem. Some boards won’t hold paint because of “mill glaze,” a glossy or waxy surface left when the board was planed at the mill.
Cure this problem by sanding glazed areas. Grain pattern can cause a more common and difficult problem. Dark bands of grain (called “latewood”) are less porous and stable than the lighter bands of wood, so paint doesn’t stick to them very well.
This isn’t a problem when those dark bands are narrow and uniform. But when they’re wide, paint soon loses its grip. In fact, you can sometimes see a board’s grain pattern right through the paint as cracks and peeling develop along the latewood grain lines (Photo 1).
If you have a few bad boards on your house, you can delay peeling by sanding thoroughly with 60-grit paper before priming. That roughens the dark bands so they hold paint better. But the only long-term cure for a bad board is replacement.
Before you get started, measure the width and thickness of your siding. Keep in mind that about an inch of the board’s face is covered by the board above. Buy matching siding at a lumberyard; most home centers don’t carry it.
To remove a bad piece of siding, you have to pull out two rows of nails: the ones in the bad board itself, and those in the board directly above. Siding is thin and splits easily, so the tricky part of this job is pulling nails without damaging surrounding boards. A cat’s paw is the best tool for digging out nails if damage to the surrounding wood doesn’t matter (Photo 1).
To get at the nails in the board above, shove a flat pry bar up under it and gently pry the board outward. In most cases, this will pop up the nailhead, so you can pull it with your hammer claw. If you run into a stubborn nail that won’t move easily, don’t use brute force and risk splitting the good board. Instead, slip a hacksaw blade behind the siding and cut the nail (Photo 2).You can’t get the new board in unless you pull the remaining shank of the cut nail (Photo 3).
Before you install the new board, lightly sand it with 80-grit paper. If you come across shiny, glazed areas, sand them thoroughly. Then prime the backside and the ends (Photo 4).
Also prime the ends of adjoining boards. This step pays off by slowing the moisture penetration that can lead to peeling at the joints. If the new siding is redwood or cedar, buy a special “stainblocking” primer. Both of these woods contain natural chemicals (tannins) that can bleed through paint, causing brownish stains. A stain-blocking primer will seal in the tannins.
Nail the new board into place with 8d galvanized nails. Use a nail set to countersink the nailheads slightly below the wood’s surface. Countersinking nails helps to keep the heads from protruding as the wood shrinks and swells.
After you prime the sunken nailheads (Photo 5), keep an eye on them for a few minutes; primer may drip out of the craters and leave runs on your siding. When the primer is dry, fill the craters with caulk. Also caulk the ends of the board, where it meets trim or the next piece of siding. Finish the job with two coats of acrylic paint.
Siding close to the roof
Too often, builders install trim and siding right up against shingles and don’t bother to seal the ends of the boards. It looks good at first, but trim and siding—whether they’re wood or a manufactured material like hardboard—soak up moisture from the wet shingles and before long the paint peels.
The solution is to cut back the siding to leave about a 1-in. gap. This keeps the siding out of contact with the shingles and allows you to seal the ends so they won’t absorb moisture.
Keep in mind that if the intersection of your roof and siding has been covered with roof cement (a thick, tarlike compound), you may have to deal with roof leaks as well. Chances are you’ll have to replace the metal flashing and some shingles after removing the cement. We won’t show that process here.
Begin by removing all the paint in the badly peeling area (Photo 1). While scraping, you might discover cracked or rotten siding that needs replacing. There’s no need to replace an entire board if only a section near the roof is damaged. Instead, cut off the damaged section with a hacksaw (Photo 3).
Don’t install any new boards until you’ve cut back the bottom edge of the siding. Cutting back siding is slow, tedious work. A backsaw or a dovetail saw with an offset handle is the best tool for the job. The fine teeth cut slowly but neatly, and the offset handle prevents scraped knuckles (Photo 4).
Don’t cut all the way through the siding or you’ll risk dulling the saw teeth and damaging the metal flashing behind the siding. Instead, stop your cut 1/8 in. or so from the flashing and then finish up by making several passes with a sharp utility knife. But be careful—it’s possible to slice the flashing if you press too hard.
With the siding cut back, take these steps: paintable water repellent followed by primer and two coats of paint on the faces and cut ends of the siding. At each step, use a disposable foam brush to coat the ends of the siding (Photo 5).Keep paint off your flashing and shingles with duct tape—masking tape may not stick to them very well.
Required Tools for this Project
Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.
You’ll also need these tools: an offset dovetail saw, metal reciprocating saw blade and holder, and a drop cloth.
Required Materials for this Project
Avoid last-minute shopping trips by having all your materials ready ahead of time. Here’s a list.