Mildew is one of the peskiest exterior paint problems, as areas of fungus growth can be found on the surface of the paint or on other surfaces in damp and shaded locations. When dealing with mildew, take proper safety precautions by wearing protective eyewear and waterproof gloves. Before taking action, confirm that you are dealing with mildew by applying a few drops of bleach to the affected area and then rinsing. If the dark spots disappear, then it’s most likely mildew.
SolutionRemove all mildew from the affected surface by power washing or scrubbing it with a diluted bleach solution (one part bleach, three parts water). Rinse the surface thoroughly and allow it to dry. Then, apply a new coat of exterior primer and paint.
- Painted surface is located in a damp area with no direct sunlight
- Substrate had mildew and was painted over without the removal of the mildew
Crusty, white salt deposits, which are leached to the surface of mortar or masonry as water passes through it. Efflorescence is often seen as a white fluffy deposit of salt crystals on cementitious (e.g. masonry) wall surfaces. Efflorescence depends on the presence of salt and moisture, and the growth of crystals will continue as long as both are present. The salts are present in the mortar, blocks, or concrete structure, and the moisture is usually attributable to some building defect. When emanating from mortar in brick or block buildings, efflorescence will appear as narrow bands corresponding to mortar joints.
- Failure to adequately prepare surface by removing all previous efflorescence.
Interior moisture escaping through the exterior masonry walls.
Exterior moisture driven through masonry walls by wind and rain.
Basement walls that are not properly sealed against ground moisture penetration.
Insufficient curing time for new cement or mortar.
If excess moisture is the cause, eliminate the source by repairing the roof, cleaning out gutters and downspouts, and sealing any cracks in the masonry with a quality caulk or sealant. If moisture is originating inside the building, consider installing vents or exhaust fans, especially in kitchens, bathrooms, and laundry areas. If moisture is being driven through the walls from the outside, apply a waterproofing coating to the outside. Remove the efflorescence and all other loose material with a wire brush, power brush, or low-pressure washing, and then thoroughly rinse the surface. If the surface is highly alkaline, wash with a mild solution of H&C Concrete Etching Solution or Muriatic Acid. Painting should be delayed if efflorescence continues.
While some of the issues discussed above are caused by natural elements, it is often possible to prevent exterior paint problems by properly prepping the surface ahead of time. Before painting, be sure to check for the following problems and address them as needed:
- Loose or peeling paint should be removed with a paint scraper or stiff wire brush. Then, sand the surface until it's smooth. Wash, rinse, and allow the surface to dry before you begin painting. Any bare areas should be spot primed before applying a top coat.
- Mildew should be treated with a solution of three parts water to one part household bleach; leave the solution on the surface for 10 to 20 minutes. Then wash, rinse, and allow the surface to dry before painting, and apply a topcoat.
- If there is a glossy sheen on the surface, it should be lightly sanded to a duller finish. Fine-grit sandpaper is best; however, tougher jobs like removing stained, peeling, or splintered areas will require medium grit sandpaper. Then, wash, rinse, and allow the surface to dry.
- If chalk is present, wash the surface thoroughly using a household detergent and a stiff bristle scrub brush. Rinse and allow the surface to dry before painting.
Once you've addressed any existing issues with the surface you'd like to paint, it's time to follow these instructions to properly prep the surface for painting:
- Starting at the top, wash down the surface using a garden hose with a high-pressure nozzle or a power washer. A house wash may be used for cleaning exterior surfaces if desired.
- Patch cracks, holes, and seams with exterior paintable caulk. Check for proper ventilation from the kitchen, laundry room, and bathroom where moisture may accumulate. Moisture from inside the house is the main cause of peeling paint on a building's exterior.
- Prime any bare wood before painting or use a paint and primer in one product.
- Apply a topcoat with a good-quality brush, roller cover, power sprayer, or paint pad by starting at the top and working down. tart with the largest exterior surface, such as siding, followed by trim, windows, and shutters.