It’s very likely that the exterior inspection recommended in our last post will turn up some problems here and there. The good news is that paint problems are usually easy to fix if you can figure out what caused them in the first place. Here are a few of the more typical problems and their likely causes; in our next post, we’ll tell you how to fix them. First you should identify if the problem is localized or general. If the problem is limited to a small area or on one side of the house it should be easy to identify and correct. If the problem exists on the entire house it may be a much larger issue and you should probably have a paint expert to inspect your home. Consult your local Benjamin Moore retailer to find an expert who can help.
Small or medium-sized blisters are a sign of moisture trapped beneath the finish and can result from several conditions:
- If wood–or any substrate–was wet when it was painted, moisture will be trapped under the paint film. If only the surface was wet, a dry sunny day is usually all that’s needed to dry it out. But if the wood was saturated–from pressure-washing, for example–several dry, low-humidity days with lots of wind will be needed before you can paint. (Pros look for substrate moisture contents between 12 to 14%–if they’re unsure about conditions, they’ll test with a moisture meter.)
- If the substrate was too hot when paint was applied, it may dry too quickly, trapping solvent vapors which can then turn into blisters. To prevent this, professionals avoid painting when the surface temperature is above 90-degrees F and don’t paint in direct sunlight.
- High humidity can also cause blistering. When water-based paints cure, the water should evaporate as fast as or faster than the solvents. In humid conditions, water cannot evaporate and the solvents end up evaporating first, causing the paint to cure while still in a water-filled state. Oil-based paints, having a slower drying rate, are especially susceptible to solvent entrapment.
- When a house is poorly air-sealed and poorly ventilated or if the walls are missing a proper vapor barrier, water vapor inside the house tends to escape through the walls. Instead of being trapped by the wood siding, water vapor passes through and starts to push the paint off, resulting in blistering.
- If interior moisture is excessive, such as in unventilated baths and laundry rooms, for example, peeling will occur on the exterior siding. Don’t try to repair and repaint before correcting this problem.
- If unfinished siding is exposed to several weeks of sunlight before painting, UV will degrade the wood and it will not hold paint well.
- Peeling will occur if there’s reduced adhesion because of dirt on the substrate or because of mill glaze, caused when the surface of newly-milled wood is hardened by dull planer blades, or when resins in the wood are drawn to the surface during the milling.
- Paint can begin to crack and peel from paint build up. Older homes that were painted multiple times with oil based paint exhibit this problem.
Paint does not have to fall off to fail. Woods such as redwood or cedar contain tannins that bleed out of the wood when they come in contact with moisture. If these wood species are not properly primed with a product specifically designed to block tannin bleed, this discoloration may end up coming through your finish coat.
Wood that stays wet for an extended period of time eventually rots. If you find wood that is soft and spongy, it has degraded to the point that it will never hold paint, and should be replaced.
Of course, not everything you uncover in your inspection is cause for concern: Expect to find some chalking or fading of the finish–both are a natural consequence of aging. Excessive chalking is probably a sign that you’ll have to repaint in the not-too-distant future. Dark patches of mildew are also likely, especially in shady or damp areas, and are unsightly rather than indications of anything more serious. Washing or scrubbing with Benjamin Moore’s Clean (product number 318) or a solution of 1 part bleach to 3 parts water should remove them.