What causes blistering in paint?

also known as: blistering, bubbling, blowing, bubbles

Contents

Description

Bubbles (or pimples) appearing in the topcoat film/application

Improper surface preparation or cleaning: tiny specks of dirt on the surface can act as sponge and hold moisture. If then the surface is exposed to sun or change in atmospheric pressure, the moisture expands and finally form blisters.
Wrong thinner: use a fast-dry thinner, especially if the material is sprayed at excessive spray gun pressure
Excessive film thickness: insufficient drying time between single coats or too heavy application of the undercoat (may trap solvents which escape later and form the blisters)
Contamination of compressed air: Water, oil or dirt in the compressed air line
Applying topcoat on wet-sanded polyester without enough time for the water to evaporate
Materials/coats are not compatible

Thoroughly clean areas before painting and make sure surface is completely dry before applying basecoat or topcoat (do not touch cleaned areas as oil from the hand would contaminate the surface)
Chose a suitable thinner for your existing paint shop conditions
Allow proper drying time for basecoats and topcoats
Drain water and clean air pressure regulator on a daily basis in order to remove trapped moisture and oil (also drain air compressor tank daily)

If damage is extensive, paint must be removed down to basecoat or substrate (depending the depth of blisters). Then refinish

In less severe cases, blisters may be sanded out, resurfaced and retopcoated