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Exterior Painting

 

Before you plan to paint your home or hire a contractor to do it, it pays to understand the basics of house paints as well as some of the common problems associated with exterior paints.

Paint that is applied to exterior wood must withstand yearly extremes of both temperature and humidity. A primary purpose of painting is to exclude moisture because moisture penetration is one of the main causes of wood deterioration. Another important purpose for painting wood is to define the architectural features and improve the appearance of the house.

House paints have three constituents in common: pigment, vehicle and solvent. Today’s pigments are manufactured inorganic particles that have the weather resistance needed for exterior exposure. Natural and manufactured pigments that have no color value and little hiding power are added for strength, texture and body. Pigments were once natural minerals such as iron oxide for barn red and clay for yellow but their hiding power and liquid absorption were inconsistent.

Here are some of the common problems with exterior paint and ways to fix them:

  • Chalking: A fine chalky powder forms on the surface of a paint film. Chalking is the paint pigment that is released by the paint binders which have broken down. Chalking is more common with light colored flat paints.  The causes include use of cheaper quality paint, over-thinning paint, and porous surfaces not properly sealed before painting. Chalking is considered dirt and must be removed before repainting.

  • Blistering: Small to medium sized bubbles of paint film are referred to as blistering. Often this is caused by painting when there is direct sunlight on the siding and the paint dries too quickly or painting when the wood is damp thus causing trapped moisture to expand the paint film. It can also be caused by house moisture escaping through the walls due to improper house ventilation. To repair the problem, scrape away the blistered paint, sand to bare wood, let the wood dry, and then sand and prime and paint. If it is a ventilation problem, make sure the walls of the home are properly ventilated before painting.

 

  • Alligatoring & Checking: These are the terms used when the paint surface resembles a reptile’s skin. Checking is a less severe form of alligatoring. These conditions are often caused because a second coat of paint was applied over the first coat of primer before the primer dried. Alligatoring can also occur if the second coat of paint is incompatible, such as a glossy paint over a latex based paint. Checking can be caused by the natural aging of several layers of older oil based paint. To fix either problem, remove the old paint, sand, prime and repaint with a flexible latex-based paint. 

  • Efflorescence: This problem occurs with painted masonry and is the crusty white salt deposits that bubble through the paint film. The salts in brick or concrete dissolve with water and then leach to the surface when the water evaporates. It can also occur if the masonry is painted before the concrete or mortar is adequately cured. To repair, first make sure you eliminate any sources of moisture. The next step is to remove the efflorescence: clean with trisodium phosphate cleaning solution, rinse with clear water and then let dry and paint.

  • Peeling Paint due to Poor Adhesion: Peeling is very common and can be caused by moisture or poor adhesion. Painting over dirty, wet or shiny surfaces or applying oil-based paint over a wet surface can all cause peeling. To repair, scrape away old peeling paint, feather sand the areas, spot prime bare areas and repaint with quality paint.

  • Peeling Paint due to Moisture: When moisture gets behind paint, peeling occurs. Moisture can come from failing caulk, leaks in a wall or roof, wood being too close to the ground or from painting when the surface is wet from rain or condensation. To repair, first fix the cause of the problem and then proceed as mentioned above.

  • Rust Discoloration: This is characterized by rust colored stains on the paint surface. The possible causes include the use of non-corrosion resistant nails, steel nails popping from the surface and weathering or sanding that has worn away any galvanized coating on the nail heads. If possible, replace steel nails with galvanized or stainless steel nails or countersink the nails. After this, caulk the hole caused by countersinking.

  • Mildew: This fungus can be caused by a combination of moisture, lack of direct sunlight and poor ventilation. It is also caused by not priming bare wood before painting. The best way to eliminate this problem is to scrub the area with a trisodium phosphate cleaning solution or a solution of 1-part bleach to 3 parts water. Let the solution sit for 15 minutes and then rinse with clean water. Then wash again with a detergent and water and let dry.

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