Painting and Decorating Concourse
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Smart painters will always test adhesion first before proceeding when there might be a problem with adhesion. When in doubt - test before proceeding with full scale painting, this will save you a lot of grief in the long run. When should you test for adhesion?
The best way to address this question is to touch on the situations in which paint has a hard time adhering to an underlying surface.
Adhesion Testing - part 1
"Clean, dull and dry". This is standard for surface preparation. House paints have a hard time adhering to:
- Glossy surfaces. The problem with glossy surfaces is that there is very little for a new coating to mechanically grip to, the substrate is simply too smooth. Another problem with glossy surfaces is that they repel a paint coating and don't allow the paint to "wet out" the surface - somewhat like water on a waxed car will bead up and will not "spread out' onto the surface of the waxed car.
- Dusty surfaces. Dusty surfaces are also "dirty" surfaces (waxy, greasy surfaces are also "dirty" surfaces too and must be cleaned) and this violates the "clean" rule of surface prep. The problem with dusty surfaces is also that the paint has a hard time wetting this type of surface too and cannot bind the loose material together to the underlying substrate. Oil paints and primers are better than latex paints for wetting and binding surfaces that are a bit dusty, but never paint over dusty surfaces without first removing the dust. Sometimes it is close to impossible to totally remove every spec of dust from a surface, in these cases I will (after doing my very best to remove the dust or paint chalk by either vacuuming, dusting, water blasting, wet mopping, wiping etc.... ) choose the best oil primer for the surface to be painted knowing that oil has a better chance of wetting any residual dust that might still be clinging to the surface. I will spot prime in several random locations and then perform an adhesion test on these spots before proceeding with full scale priming and painting to be sure that I will have proper adhesion.
- Dirty surfaces: Under the general "dirty" heading we will include waxy and greasy and otherwise "contaminated" surfaces.
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