Under the blistering exposure to sun, frequent soakings by rain, and radical temperature shifts, the paints that cover exterior siding and trim surfaces face some of the most demanding conditions possible. Modern paint chemistry makes today’s paints remarkably adept at handling these situations, and the house surfaces that once required painting every two or three years can now sometimes go a decade before they require repainting. But under certain conditions—or when the preparation or application has been less than ideal—there are a number of common problems that occur with exterior paint jobs. Understanding the origins and solutions for these ten common problems will help you address them quickly and avoid them in the future.
- Blistering Paint
Blistering paint is identified by small- to medium-sized bubbles or blisters under the paint film. It is most commonly seen on wood siding and trim.
- Paint was applied in direct sunlight on a hot surface, which trapped solvent vapor as the paint dried too quickly.
- The Paint was applied when the wood was damp, causing trapped moisture to expand the paint film.
- Dew, rain or very high humidity penetrated after latex paint dried—a common problem if the latex paint was of lower quality or if the substrate surface preparation was inadequate.
- House moisture escaped through the walls due to improper house ventilation.Repair and Prevention
- Scrape away blistered paint, and sand to bare wood. Let wood completely dry before painting.
- Make sure to sand, prime, and paint in non-direct sunlight and in non-humid conditions.
- Use high-quality latex paint.
- If due to lack of home ventilation, corrective repairs must be made to properly ventilate the home’s walls, roof, and eaves, bathrooms, etc.
- Check and repair any loose or missing caulking around windows and doors.
- Consider providing siding ventilation.
- Alligatoring and Checking
IAlligatoring is a type of paint film failure in which the surface develops a cracked pattern with deep relief, resembling a reptile’s skin. Checking is a similar failure, but it is less severe and is characterized by long, fairly evenly spaced cracks in the paint film, having shallow relief or depth. Occasionally checking may become severe in some areas, leading to a deeper crack or split in the paint.
Possible Causes (Alligatoring)
- The second coat of paint was applied over the first coat of primer or paint base coat that had not yet fully dried.
- The second coat of paint was applied over an incompatible paint, such as a glossy paint or a hard oil enamel over a latex-based paint.
- Oil-based paint has naturally aged and lost its elasticity, leading to cracks caused by fluctuations in temperature.Possible Causes (Checking)
- Natural aging occurred with several layers of older oil-based paint. As the material that was painted (usually wood) contracts and expands over time, the paint has to move, and it “checks” as it loses elasticity. Repair and Prevention
- Remove the old paint, then sand, prime and repaint with a flexible latex-based paint.
- Use high-quality latex paint.
A problem of painted masonry construction, efflorescence is identified by crusty white salt deposits bubbling through the paint film from an underlying masonry structure. It is caused by salts in the brick or concrete dissolving with water and then leaching to the surface as the water evaporates.
- Surface preparation was poor; prior efflorescence was not entirely removed and washed before the surface was repainted.
- Heavy moisture migrated through exterior masonry walls from inside the home.
- Inadequately waterproofed basement walls allowed groundwater penetration.
- Masonry was painted before the concrete or mortar had adequately cured and dried out.
- Cracks in the masonry wall or poor tuckpointing have allowed water to get behind masonry wall.Repair and Prevention
- If moisture is getting into the masonry wall, eliminate the source of moisture by properly tuckpointing any cracks or missing mortar in the wall or patching concrete with a latex concrete patch; clean out gutters and downspouts, and caulk joints around windows and doors with a butyl rubber caulk.
- If moisture is migrating through the wall from the outside (e.g., basement wall), apply waterproofing to the outside of the wall.
- Remove all efflorescence and any loose flaking, chalking paint with a wire brush, scraping, or power washing. Then clean the area with a trisodium phosphate cleaning solution and rinse with clean water. Let completely dry, then paint with a high-quality latex house paint.
Chalking is identified by the fine chalky powder that forms on the surface of a paint film. Although some chalking is a normal way in which paints self-clean when exposed to the sun and rain, excessive chalking can indicate paint failure. In dry arid climates where there is little rain, chalking can become excessive. Chalking is actually the paint pigment released by the paint binders that have been broken down by exposure to the weather. Chalking is especially common with very light-colored flat paints, especially lesser quality oil-based paints containing high levels of pigment extenders. When chalking gets severe, it may run off and stain the surrounding construction.
- Cheaper-quality exterior paint was used, containing high levels of pigment extenders.
- Improper paint (such as interior paint) was used in an exterior application.
- Paint was applied over lower-quality factory-finished aluminum siding.
- The paint was over-thinned before it was applied.
- Porous surfaces were not properly sealed before painting.Repair and Prevention
- Chalking must be removed before repainting. Remove chalking by power washing or scrubbing with a trisodium phosphate cleaning solution and rinse with clean water. Let dry and paint with a high-quality latex house paint.
- To clean brick areas stained by chalking runoff, the masonry should be scrubbed with a specialized masonry cleaning solution. If staining persists, a professional cleaning contractor may be required to clean the brick.
- Sagging or Running
This paint failure is easily identified as paint film with a droopy, dripping appearance.
- Application of a coat of paint was too heavy or overloaded.
- Paint was thinned too much at the time of application.
- The paint was applied in poor environmental conditions, such as when temperatures were too cool or when humidity was too high.
- The paint was applied to a high-gloss surface that was not first primed. This prevents the paint substrate from having the “tooth” necessary for the finish coat to adhere.
- Painted surface was not clean or properly prepared at the time of application.Repair and Prevention
- If you catch the sagging while the paint is still wet, use a brush or roller to redistribute the excessive paint evenly.
- If the paint is dried, sand the uneven area and lightly reapply paint.
- If the paint was applied to a glossy surface, sand the glossy surface to dull it and create a “tooth” for the paint to adhere, or apply a primer and repaint.
- Paint using two light coats instead of one very heavy coat.
- Do not overload the paintbrush. Follow proper technique for use of a paintbrush.
Mildew is a fungus that feeds and grows on the paint film or caulk and is identifiable by its gray, brown, green, or dark black splotchy spots.
- Moisture, poor ventilation and lack of direct sunlight have combined to create an environment where fungus can thrive. The underside of soffits and eaves are especially prone to mildew.1
- Paint was applied over a surface or prior paint film that still had mildew.
- A lower-quality paint was used, without adequate mildewcide.
- Bare wood was not primed before painting.Repair and Prevention
- Wearing eye protection (goggles) and rubber gloves, scrub vigorously with a trisodium phosphate cleaning solution or a household bleach solution of 1 part bleach to 3 parts water.
- Let the solution set on the cleaned are for 10 to 15 minutes.
- Rinse with clean water.
- Wash the area with a detergent solution and rinse again.
- Let completely dry and paint with a high-quality latex house paint.
- Rust Discoloration
This problem is characterized by rust-colored, reddish-brown to black stains on the paint surface.
- Non-corrosion-resistant nails were used to attach siding, rather than galvanized zinc-plated or stainless steel nails.
- Steel nails have come into contact with the air.
- Steel nails have popped up from below the surface.
- Excessive weathering or sanding has worn away galvanized coating on nail heads.
- Tannic acid from moist wood (e.g., oak) has reacted with steel nails, creating a black stain.Repairs and Prevention
- If possible, replace steel nails with galvanized or stainless steel nails.
- If rusted nails can’t be removed, then remove rust by sanding nail heads to bare metal and countersink them. Then, prime with a stain-blocking, rust-inhibiting primer. Caulk, fill, or patch depressed nail heads and sand smooth, and paint with high-quality paint.
- Peeling Paint Due to Poor Adhesion
Peeling paint is a very common paint problem that can be caused either by moisture or poor adhesion. Peeling due to poor adhesion is characterized by the paint peeling and separating from an earlier paint layer (intercoat peeling) or from the substrate, leaving some paint behind. Sometimes, portions of earlier paint layers are visible under the curling, peeling paint layer.
- Paint was applied over a surface with poor paint surface preparation, such as being dirty, wet or shiny.
- Underlying paint had poor adhesion prior to being repainted.
- An oil-based paint was applied over a wet surface.
- Blistering paint was allowed to progress. Blisters will eventually break and begin peel.
- Lower-quality paint was used.Repair and Prevention
- Scrape away old peeling paint and feather-sand affected areas.
- Spot prime bare area.
- Caulk as required with appropriate caulking product.
- Repaint with a high-quality acrylic latex house paint.
- Peeling Paint Due to Exterior Moisture
Peeling due to moisture can be distinguished from other causes by the large peeling sections that expose bare wood underneath. Unlike peeling due to adhesion problems, where peeling may be spotty, moisture-related peeling causes much larger areas to peel away, often around windows, doors, and gutters.
- Moisture has infiltrated behind paint film due to failing or missing caulk, leaks in roof or wall systems, or being too close to the ground.
- Faulty guttering or missing ventilation has caused ice dams or water to back up.
- Paint was applied when the surface was wet from condensation or rain.Repair and Prevention
- Ensure proper drainage of gutters and downspouts flowing away from home.
- Eliminate the source of moisture by installing exhaust fans, soffit vents, siding vents, louvers, fans, or dehumidifiers.
- Repair and replace missing or damaged caulk.
- Scrape away old peeling paint and feather-sand affected areas. Spot prime bare area. Caulk as required with appropriate caulking product. Repaint with a high-quality acrylic latex house paint.
- Peeling Paint Due to Interior Moisture
The last cause of peeling paint is interior moisture, characterized by cracking and gentle peeling away of the paint from the substrate as it loses adhesion due to the moisture. Moisture originating from behind the paint film, or frontal moisture that forces its way through the paint film, can create this type of paint failure.
- High humidity areas, such as bathrooms, kitchens, hot tubs and wet basement areas, have created humidity that penetrated the paint film.
- Leaking flashing around a chimney or other exterior wall/roof intersection have allowed water to seep into the house and wet the plaster from behind the paint film, causing the paint to separate from the substrate.Repair and Prevention
- Ventilate high-moisture areas such as bathrooms by providing an exhaust vent fan that removes humidity and discharges it to the outside.
- Ensure proper ventilation of the roof, walls, and soffits.
- Repair missing or damaged flashing at chimney or other wall/ roof connections.
- Scrape away old peeling paint and feather-sand affected areas. Spot prime bare area. Paint with high-quality acrylic latex paint.