Exterior Inferior? The Proof Is Seldom in the Paint

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

* Blistering is the earliest stage of peeling. It is usually caused by moisture trapped under the new paint coat or by poor surface preparation. If it occurs within the first few weeks after painting, it’s probably caused by trapped moisture.

While latex paint can usually be applied to damp surfaces without problem, alkyd and other oil-based paints form a moisture-barrier skin that traps water inside. The water turns to vapor and forms blisters.

To avoid this, never paint with alkyds soon after a rainstorm, when the relative humidity is more than 85%; 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 degrees.

If blisters appear after a month or so, the problem is probably poor surface preparation. If you first washed the surface 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. It is merely a later manifestation of blistering. Severe peeling may also indicate the use of a poor primer, or a heavy film of dirt, grease or dust. Prevention involves sanding or wiping the old finish with a de-glossing liquid. Then follow the manufacturer’s directions as to what primer may 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 paint used. Sanding and then applying a new coat of wood primer will usually solve the problem. If the new paint shows signs of coming loose, complete removal of the old paint is required.

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

* Chalking or powdering characteristics are designed into some paints 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. In severe cases, you may have to apply a bonding primer or sealer before painting.

* Mildew manifests itself as patches of black spots. Though most exterior paints contain mildew-inhibiting ingredients, none work 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 1 quart of household bleach. Wear long pants, a long-sleeved shirt, gloves, goggles and a respirator to avoid breathing the fumes.

* Stains that bleed through paint are often the result of sap from knots in the wood seeping through the surface. They can also 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, such as pigmented shellac-base sealer, and then apply paint.