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Problem Solving
Diagnose Common Paint ProblemsTake a good look at your house before you start painting. You may have to correct some of the wrongs that the previous painter overlooked in desiring to get the job done fast. You may have peeling paint as shown in Figures A – C.
Poorly Prepared SurfaceYou may notice the finished coat of paint peeling away from another coat underneath (Figure A). This is the result of painting over a poorly prepped surface. Usually the surface wasn’t cleaned before painting or the primer coat was left too long before the finish coat of paint was applied. You can remedy this situation by firmly scraping away the paint to get at the surface below. Scrape until you get down to a solid surface that may be part bare wood or a sound, previously painted surface. Sand and clean the surface thoroughly, let it dry, and prime all bare wood and spot-prime any small bare spots.
Figure A
Excess Moisture
Sometimes you find paint and primer falling away from the bare wood surface (Figure B). This is most likely caused by water getting behind the wood or even moisture from the home’s interior. You can’t repaint here unless you stop the source of the moisture migrating through the walls, especially from bathrooms and kitchens. Adding ventilation such as an exhaust fan in the room can frequently help the problem. Many older homes have no vapor barrier, but sometimes applying a vapor barrier paint on the inside will do the trick. If you’re stymied, consult a building contractor to help you solve the problem. Then scrape and sand to remove the loose paint.
Figure B
Excess moisture getting behind the
siding
Another common problem is cross-grain cracking, sometimes referred to as “alligatoring.” The source of this problem is usually paint buildup from several layers of oil-based paints. Unfortunately, there’s no magic bullet for this fix. You’ll have to scrape off all the old paint down to bare wood and then sand the surface. Take precautions and gather this paint onto dropcloths or plastic for disposal because it may contain lead. Don’t keep applying layers of paint to areas that don’t need it such as porch ceilings and eaves where the surfaces are protected. Often a good cleaning is all they need.
Figure C
Alligatoring from too many layers of oil-based paint Other Problems
You may find dark mildew spots on the finished coat of paint along shady areas of the house. Buy a special cleaner at paint supply stores to scrub the surface. You can usually stop mildew by increasing exterior airflow in that area, trimming plants close to the house, and channeling water away with gutters and downspouts. If the area is tough to air out, you can get mildewcide additives for your finish coat of paint.
Another problem is chalking, where old paint surfaces get powdery. This is natural for old paints, but you’ll have to power wash or scrub the surface and do some light sanding to remove the chalking before applying paint.
Fill Large Gouges Before PrimingFill large holes and gouges with a two-part resin filler such as Minwax High Performance Wood Filler. You have to mix these setting types of fillers, but they stick better to wood than other fillers. Remove any paint around the area before filling. You can fill nail holes with them too.
For small, shallow blemishes, use an exterior spackling compound. Cracks can be filled with exterior caulk after priming.
Click image to enlarge.
1. Overfill each repair and then shape it, once it
has set, with a file, sharp chisel and sandpaper. Blemishes deeper than 1/2 in.
will need additional applications. Once the patch is dry, shaped and sanded,
prime it to protect it from moisture.
Click image to enlarge.
2. Feather the edge of your scraped areas with a
power sander to get rid of sharp edges. These ridges can break the finished
paint surface later and allow moisture to get behind the paint. After sanding
(use 80 to 100 grit), use a dry brush to whisk away any surface dust,
especially on horizontal surfaces like windowsills.
Power sanders cut fast. Use a 60-grit paper for heavy ridges followed by 100-grit for a smooth look. Also sand shiny, old paint surfaces to give the topcoat better bite.
TIPSand all old, bare wood. Paint won’t stick to wood once it has weathered.
Click image to enlarge.
Use a Stain-Blocking Primer
You can choose either an oil or a latex primer and get great results. Oil primers, however, are generally more effective on new wood, metal and previously chalked surfaces. If you’re priming over bare woods that have a high tannin content, such as cedar and redwood, ask your paint supplier for a special stain-blocking exterior primer. Stain-blocking primers will prevent a “bleed-through” of tannin through the primer and the topcoat and stop old, rusty nailheads from bleeding through as well.
TIPYour paint supplier can add pigment to your primer to get it close to the topcoat color. This is especially helpful when your topcoat is a darker color. You may be able to cover the primed area and old paint surface with one coat of paint.
TIPAlways try to avoid priming or painting in direct sun. The extra heat can dry the primer and paint too quickly and prevent adequate penetration. It can also cause oil paints to develop blisters that’ll ruin the skin of the finish coat of paint.
Click image to enlarge.
3. Spot-prime nailheads and knots with a special
stain-blocking primer to prevent unsightly bleed-through from rust or wood
resin. A pigmented shellac (BIN, for example) is a good product for this
use.
Click image to enlarge.
4. Work the primer into cracks and especially
where trim pieces meet siding. Even out the primer with long brush strokes and
check for drips. Remember to work the primer under the siding laps and into
tight spaces and hard-to-see spots. Surfaces that still have old paint that’s
adhering well don’t need a primer.
With all the caulks available at home centers and paint supply stores, it can be hard to know what kind of caulk to buy to seal gaps. Most professionals agree that acrylic caulk and siliconized acrylic caulk are the best for caulking around windows and doors and against corner boards. These caulks are paintable, long lasting and easy to clean up.
Caulk after priming. The caulk sticks best to a primed surface. Squeeze enough caulk into the gaps to get a smooth bead that fills the void. Excess caulk will look sloppy and will only increase the possibility of working loose over time.
5. Caulk all the seams and cracks once you’ve
primed the surface to keep out moisture and hide unsightly dark lines. Wipe
excess acrylic caulk and shape it with a moist rag as you apply it. Let the
caulk set (usually a couple of hours) before painting over
it.
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