Intercoat Peeling By Vancouver’s Best Painters
Paint Failure by Rick Anderson (Vancouver’s Best Painters)
INTERCOAT PEELING UNDER EAVES AND COVERED PORCHES (SCALING AND CORNFLAMNG)
Intercoat peeling often occurs under eaves, covered porches, and other protected areas. The loose paint scale resembles cornflakes, which is why it is sometimes referred to as cornflaking.
Protected or shaded areas on buildings are susceptible to condensation and salt deposits. Water-soluble chemicals in paint films contain salts which are pulled to the surface by moisture. When the moisture evaporates, the chemicals are left on the surface in crystalline powder form. This formation of crystals is due to sulfur dioxide, which is produced in varying amounts by burning commercial fuels that are carried through the air. When the chemical comes into contact with water, an acid is formed which reacts with some of the pigments in paint and leaves crystalline powder deposits.
The powder is not noticeable on white paint. On colors, it resembles salt. This depositing also occurs on siding, but the salts are washed away by rain.
These chemical salts are hygroscopic; meaning they will absorb moisture through an existing coat of finish that is applied over them if they are not removed prior to painting. The result is that a year or so later, the salts draw moisture through the existing coating film and form a pressure on the back side of that film. Gradually, that pressure becomes greater than the adhesive strength of the coating film to the substrate, and it is forced off.
Salts attract moisture, even after new coats of paint are added to the surface. When freezing temperatures occur, any moisture lingering on the salt layer freezes and expands, forcing the topcoat of paint outward, thus causing intercoat peeling.
Scaling also can be evident in protected areas where gloss paints have been applied. Lack of weathering leaves these surfaces hard and shiny. A new coat of paint will not adhere properly to the slick surfaces without correct surface preparation.
Solution
Protected surfaces should be washed with detergent to remove dirt from the paint. They then should be rinsed with a strong stream of clean water to take off the salts.
When the surface is dry, remove all loose paint with a scraper or wire brush and sand these areas, along with any glossy surfaces. Apply one or two coats of latex- or oil-based house paint.
Rick Anderson
www.vancouverindustrialpainting.com
local: 604-PAINTER
Toll Free: 1-800-PRO-PAINTER
Posted in Painting Articles