This refers to a white, salt-like substance on the paint surface. Frosting can occur on any paint colour, but is less noticeable on white paint or lighter tints. On masonry, it may be mistaken for efflorescence.
- Protected areas (under eaves and on porch ceilings, for example) that do not receive the cleansing action of rain, dew and other moisture.
- Using dark-coloured paints that have been formulated with a calcium carbonate extender.
- Applying a dark-coloured paint over a paint or primer containing calcium carbonate extender.
Frosting can be a stubborn, albeit uncommon, problem, and is often difficult to remove by washing alone. Moreover, the condition can recur, bleeding through to the surface even after a new topcoat has been applied. In extreme cases, it can interfere with paint adhesion.
The best remedy is to remove the frosting from masonry using a wire brush, or from wood surfaces by sanding, and rinsing them thoroughly. Apply a solvent-based primer before adding a coat of high- quality exterior paint.