Alligatoring and Checking
“Alligatoring” occurs when the paint film takes on a cracking pattern of deep relief resembling a reptile\’s skin, such as that of an alligator. “Checking” is a similar failure but is less severe and is characterized by long, fairly evenly spaced cracks in the paint film having shallow relief or depth. Alligatoring happens when a second coat of paint is applied over a first coat of primer or paint base coat before it has dried or a second coat of paint applied over an incompatible paint such as a glossy paint or a hard oil enamel over a latex based paint. Fluctuation in temperature can also cause oil based paints naturally aging and losing the little elasticity to crack. Checking occurs when natural aging of several layers of older oil based paint happens. Expansion and shrinking over time can cause the paint to move and lose its elasticity, thus causing “checking” problems.
- Remove the old paint, sand, prime and repaint with flexible latex based paint.
- Use high quality latex paint.
This problem is identified by crusty white salt deposits that bubble through the paint film from a masonry structure. This occurs when salts in the brick or concrete become dissolved with water and then leach to the surface as the water evaporates. Poor paint surface preparation where prior efflorescence was not entirely removed and washed before the surface was repainted can be the cause of this problem. Heavy moisture migrating through exterior masonry walls from inside the home, inadequate waterproofing the basement walls allows ground water to penetrate can also cause this. Painting masonry construction before the concrete or mortar had adequately cured and dried out or cracks in masonry wall or poor tuckpointing that allow water to get behind masonry wall are also some causes for efflorescence.
- Tuckpointing cracks or missing mortar in the wall or patching concrete with a latex concrete patch, clean out gutters and downspouts, caulk joints around windows and doors with a butyl rubber caulk.
- Apply waterproofing to outside of wall.
- Make sure that you remove all efflorescence and loose flaking, chalking paint with a wire brush, scraping or power washing before repainting.
- Clean area with a trisodium phosphate cleaning solution and rinse with clean water.
- Let completely dry and paint with a high quality latex house paint.
The emergence of fine chalky powder that forms on the surface of a paint film is what chalking is about. Some chalking is a normal way paints self clean when exposed to the sun and rain, but excessive chalking can be a paint failure. This can occur commonly in dry arid climates where there is little rain. Paint pigment released by the paint binders which have been broken down by exposure to the weather is the source of chalking and is typical of very light colored flat paints, especially lesser quality oil based paints containing high levels of pigment extenders. Over-thinning the paint and not properly sealing a porous surface before painting can also cause chalking.
- Remove chalking before repainting, 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.