Chalking is the breakdown of a coating binder due to exposure to the ultra-violet (UV) rays of the sun. Causes include:
i) Failure to properly prime and seal a surface
ii) Over thinning the paint
iii) Spreading the paint too thinly
Oil-based paints are more prone to chalking than acrylics. While it is normal for paint to wear over time, excessive chalking must be resolved to ensure that the new coat of paint will bond.
Wipe your hand across the surface. If chalk appears, do the following:
Wash surface with a mild solution of TSP and water.
Agitate with a stiff brush.
Rinse with clean water.
After the surface has completely dried, rub it with your finger.
If no chalk is evident, surface may be coated.
If chalk residue remains, a surface conditioner should be sued prior to the coating. Consult your paint expert to see which products are recommended.