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Brush up on house-painting basics

From peeling to mildew, tips can save you time, $$

SHARE Brush up on house-painting basics

Usually it's the paint itself that gets the blame for paint problems on your home's exterior. In most cases, the cause lies elsewhere. Here are some common problems and ways to prevent them.

Blistering is the earliest stage of peeling and is usually caused by moisture trapped under the new paint coat or by poor surface preparation. If it occurs within the first few weeks, it's probably caused by trapped moisture. While latex paint can usually be applied to damp surfaces without any problem, alkyd and other oil-based paints form a moisture-barrier skin that traps the water inside. The water then turns to vapor and forms blisters. To avoid this, never paint with alkyds after a rainstorm, when the relative humidity is more than 85 percent, while dew is on the siding, or too soon after you've washed the old surface. Also, never paint when the temperature is more than 90 F.

If the blisters appear after a month or so, the problem is probably poor surface preparation. If you washed the surface down with detergents, did you take the time to rinse completely? Unless such films are removed before painting, they can cause blistering. Also, glossy surfaces must be given a light sanding so the new paint will grip well.

Peeling is the curling of large pieces of dried paint and is merely a later manifestation of blistering. Severe peeling might also indicate use of a poor primer, or a heavy film of dirt, grease or dust. Prevention involves sanding or wiping the old finish with a deglossing liquid. Then follow the manufacturer's directions as to what primer might be required before applying the top coat of paint.

'Alligatoring' is a cracking and flaking of the paint in a square pattern. It can result from applying paint over a previous coat that had a high-gloss finish that was not sanded, use of the wrong primer or use of old paint, particularly paint that's been stored in an unheated space and allowed to freeze.

To repair the condition, sand the surface smooth and apply the proper primer before applying a new top coat.

Checking is a series of long lines, with shorter check marks crossing between, usually caused by the wood underneath expanding and contracting. This can be a problem with exposed plywood siding regardless of the kind of paint used. Sanding and then applying a new coat of wood primer will usually solve the problem. But if the new paint shows signs of coming loose, complete removal of the old paint is required.

Wrinkling results in a crinkled surface that is caused by interfering with required drying time. Contributing factors are a too-thick finish coat, building up of too many layers, undercoat that was not completely dry, wrong solvent or improperly stirred paint. Repair by sanding smooth and applying proper primer before painting top coat.

Chalking or powdering characteristics are designed into some paints in order to keep the surface looking new. Chalking of old paint can interfere with proper bonding of a new coat, so scrub off as much as possible beforehand.

Mildew manifests itself as patches of black spots. Though most exterior paints contain mildew-inhibiting ingredients, none works under all circumstances. Remove mildew by washing down the affected area with a bleach solution. Use one-third cup powdered laundry detergent, two-thirds cup of household cleaner containing trisodium phosphate, and one quart of household bleach.

Stains that bleed through the paint often are the result of sap from knots in the wood seeping through the surface. But they also can be caused by rust from nails and hardware. Many discolorations bleed through coat after coat of paint, so repainting alone is not the answer. Instead, apply a primary coat of stain-killer, and then apply your paint.