Preventing blistering and peeling
A Popular Misconception
A popular misconception is that blistering and peeling, two of the most common exterior painting problems, can be blamed on an inferior paint product. To the contrary, the paint itself is seldom at fault.

Blistering and peeling are almost always caused by moisture, either moisture vapour or actual moisture, usually water. During the winter months, excess moisture building up inside the house escapes through walls and into exterior paint. When the summer sun heats the siding, water trapped inside the paint film is vaporized with the resulting pressure causing the topcoat to blister.

Exterior blistering can also be caused by painting in direct sunlight, particularly when heat-absorbent dark colour paints are used. Under a hot summer sun the paint film can dry too rapidly, trapping solvents which later vaporize and once again cause pressure against the topcoat.

To determine which type of blistering you have, break open one of the blister bubbles. If you find bare wood underneath, the cause is probably moisture. If you find paint, the blistering is most likely a result of painting in direct sunlight. In either case, all blistered paint should be removed by scraping and sanding prior to any repainting. In the case of heat blisters, the prime coat is usually not affected so you can repaint without priming. But do so when the sun is not falling directly on the surface. If actual moisture is the culprit, however, the source must be removed. Otherwise you will continue to have a problem with blistering and peeling, year after year, no matter how often you repaint.

There are number of ways for water to reach painted wood. Worn-out caulking or uncaulked joints can allow moisture to seep into adjoining wood surfaces. Ice-filled or trash-choked gutters cause moisture to build up under shingles. Moisture-laden air trapped inside tightly constructed buildings permeates exterior walls when heated. Also contributing to the problem are damp basements, leaking roofs, vegetation giving off moisture too close to the wood and wood that's damp with rain or dew when painted.

THOROUGH INSPECTION
A thourough inspection of the exterior of your home is necessary, paying extra careful attention to window and trim areas and other joints. Also check for moisture seepage between the porch slab and your house and through leaks in the roof.

Once you have located the problem area or areas, you're on the home stretch towards ridding yourself of the problem. Begin by repairing any loose caulking. Install vents to relieve moisture as required in kitchen, bathroom and laundry areas. Attic louvres, exhaust fans and dehumidifiers are also effective in alleviating moisture problems.

Peeling from moisture on wood siding can be corrected by inserting small metal wedges or shims under each board where it is nailed to a stud. These pry the boards away from the siding and provide sufficient back ventilation.

If you discover moisture is rising from the ground through masonry, you should waterproof the foundation with a specially designed coating. If wood is touching the ground, remove that portion of the wood. Siding should come down no further than 6" above the ground.
Be sure to check the roof for signs of leakage and clean out any gutters and downspouts. If you suspect vegetation is a cause of peeling, cut it back away from your house.

Scrape and sand the peeling paint down to bare wood and prime all exposed areas before repainting. Allow primer to dry for a day or two before applying the topcoat. Using two coats of the topcoat can more than double the life of the paint job. Use of a high quality product like General Paint is also important to ensure good results and a long-lasting paint job.

If you can't eliminate the source of moisture, try repainting the stripped and sanded wood with a latex paint which is more permeable than oil or alkyd coatings and may allow the moisture vapour to escape through the film.

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Scott Smith Painting
Phone: 831-438-4198
Ca. Lic. 795360

scott@scottsmithpainting.com