The most common causes of flaking in paint are moisture underneath the coat and also paint applied over oil, dirt, grease or onto a poorly prepared, powdery surface. Flaking simply means it is the detachment of paint film (the breaking of coating system right from the primer to the top finishing coat) from the underlying surface in the form of flakes or scales. It is very important to check the surface before painting. Surface should be free from dust, grease, etc..
Cracking and then ultimately flaking of paint can occur for a various reasons. The main reason for flaking to occur is the moisture penetration through cracks on the coatings resulting in the loss of bond between surface and paint film. Poor surface preparation is also the leading cause of flaking in paint. Sometimes cleaning with solvent can left residue on surface and ultimately it can lead to flaking in paint. Using lower quality paint can cause flaking as it comes with poor flexibility and adhesion property. Almost all the paint film have elasticity and there not having this property can lead to flaking of paint film. Almost all the materials have tendency to undergo expansion and contraction during temperature variation and if paint film does not poses the elasticity then cracking will occur.
Flaking can also result if applied paint is too thin due to overspreading (higher-than-recommended spread rate) or excessive thinning. These practices tend to diminish the paint’s final film thickness, so that it is more vulnerable to cracking and flaking.