Easy House Painting Tips - Newsletter August, 2008

Table of Contents
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Exterior Paint Problems - having problems with peeling, blistering or cracking paint?

Exterior Repainting Tips - remember: a coat of fresh paint will not glue down a coat of old paint that's ready to crack and fall off.

Peeling
Moisture, such as rain and dew, can penetrate a paint coat and result in cracking, peeling, discoloration and premature paint failure. These problems may be observed in both heated and unheated buildings and are more pronounced on edges and ends of boards and are also observed where water is held on the surface. Porous paints are particularly vulnerable to moisture penetration.

Inside moisture (water vapor) can destroy paint on the outside of a building by diffusing through the walls. Water vapor from cooking, dish washing, clothes dryers, bathing and normal respiration by an average family of four can contribute three gallons of water per day to the humidity. If the inside of all exterior walls does not have a vapor barrier or if the vapor barrier is improperly installed, water vapor passes into the walls during cold winter weather and condenses to a liquid. The water eventually soaks into the siding and wets the paint. This is a common cause of blistering and peeling. The problem is particularly pronounced around bathrooms, laundry rooms, kitchens and other areas of high humidity.

To reduce water vapor in the house, vent high humidity areas such as kitchens and bath areas to the outside. Clothes dryers should be vented directly to the outside and not to the attic, basement or crawl space. Mechanical humidifiers add large quantities of moisture to the air and should not be used if paint peeling is a problem.

Blistering
Temperature blisters are bubble-like swellings that occur on the surface of the paint film as early as a few hours or as long as one to two days after painting. They occur only in the last coat of paint. They are caused when a thin dry skin has formed on the outer surface of the fresh paint and the liquid thinner in the wet paint under the dry skin changes to vapor and cannot escape. A rapid rise in temperature, as when the direct rays of the sun fall directly on freshly painted wood, will cause the vapors to expand and produce blisters. Usually only oil based paint blisters in this way. Dark colors which absorb heat and thick paint coats are more likely to blister than white paints or thin coats.

To prevent temperature blisters, avoid painting surfaces that will soon be heated. "Follow the sun around the house" for the best procedure. Thus, the north side of the building should be painted early in the morning, the east side late in the morning, the south side well into the afternoon, and the west side late in the afternoon. However, at least two hours should elapse before the fresh paint film cools to the point where condensation will occur.

If blistering does occur, allow the paint to dry for a few days. Scrape off the blisters, smooth the edges with sandpaper and spot paint the area. Moisture blisters are also bubble-like swellings on the surface of the paint film. As the name implies, they usually contain moisture when they are formed. They may occur where outside moisture such as rain enters the wood through joints and other end grain areas of boards and siding. Paint blisters caused by outside water are usually concentrated around joints and the end grain of wood. Paint failure is most severe on the sides of buildings facing the prevailing winds and rain. Blisters may occur in both heated and unheated buildings.

Moisture blisters may also result from inside liquid water moving to the outside. Plumbing leaks, overflow of sinks, bathtubs or shower spray and improperly sealed walls are sources of inside water. Moisture blisters usually include all paint coats down to the wood surface. After the blisters appear, they dry out and collapse. Small blisters may disappear completely, fairly large ones may leave a rough spot and in severe cases the paint will peel. Thin coatings of new, oil-based paint are the most likely to blister. Old, thick coats are usually too rigid to swell and form blisters. Therefore, cracking and peeling will usually result. Elimination of the moisture problem is the only practical way to prevent moisture blisters in paint. The moisture source should be identified and eliminated to avoid more serious problems such as wood decay or rot and loss of insulating value.

Cracking
Cross-grain cracking occurs when paint coatings become too thick. This problem often occurs on older homes that have been painted several times. Paint usually cracks in the direction it was brushed onto the wood. Once cross-grain cracking has occurred the only solution is to completely remove the old paint and apply a new finishing system. To prevent cross-grain cracking, follow the paint manufacturer's recommendations for spreading rates. Do not repaint un-weathered, protected areas such as porch ceilings and roof overhangs as often as the rest of the house. If possible, repaint these areas only as they weather and require new paint. However, if repainting is required, be sure to scrub the areas with a sponge or bristle brush and detergent in water to remove any water-soluble materials that will interfere with adhesion of the new paint.

Latex paints are generally easier to use since water is used in clean-up. They are also porous and, thus, will allow some moisture movement. In comparison, oil-based paints require organic solvents for clean-up, and some are resistant to moisture movement. Paints are the only way to achieve a bright white finish. However, they, especially oil based paints, are subject to peeling where moisture is a problem.

If a new paint coat is to be successful over a problem area, moisture problems must be eliminated. Good surface preparation is also essential. If the wood has been completely stripped or is being painted for the first time, it should be brush treated with a paintable water-repellent preservative or water repellent. This treatment will reduce the uptake of moisture by the wood. After the water-repellent preservative or water repellent has dried for at least two warm days, following manufacturers specifications, apply an oil-base primer or a stain blocking latex primer, followed by at least one top coat of high quality acrylic latex paint. One top coat of paint should last four to five years, but two top coats can last up to 8 or 10 years.

If only isolated areas of the paint coat have failed by peeling to the bare wood, spot painting may be the best alternative. First, scrape away all loose paint. Sandpaper or "feather" the edges of any remaining paint left smooth with bare wood. Clean the old painted surface by scrubbing with a sponge or bristle brush. Rinse the scrubbed surface with clean water. Wipe the surface with your hand. If the surface is still dirty or chalky, scrub it again using a detergent, and rinse it with clean water. After the surface has been thoroughly dried, apply one coat of a high-quality latex primer.

To avoid future separation between paint coats, the first top coat should be applied within 2 weeks after the primer and the second coat within 2 weeks of the first. As certain paints weather they can form a soap-like substance on their surface which may prevent proper adhesion of new paint coats. If more than 2 weeks elapse before applying another paint coat, scrub the old surface with water using a bristle brush or sponge. If necessary, to remove all dirt and deteriorated paint, use a mild detergent. Then rinse well with water, and allow the surface to dry before painting.

Temperature blistering is most common with thick paint coats of dark colors applied in cool weather. The blisters usually show up in the last coat of paint and occur within a few hours to 1 or 2 days after painting. They do not contain water. Oil-base paint may be applied when the temperature is 40 degrees F or above. A minimum of 50 degrees F is desired for applying latex-based paints. For proper curing of the paint film, the temperature should not drop below 50 degrees F for at least 2 hours after paint application. Low temperatures will result in paint failure. To avoid wrinkling, fading or loss of gloss of oil base paints and streaking of latex paints, paint should not be applied in the evenings of cool spring and fall days when heavy dews form before the surface of the paint has thoroughly dried.