Causes

1. Poor application technique.
2. Wrong thinner used or too much thinner used.
3. Spray booth is too cold.
4. Surface contamination by greases, silicone, oil, dirt etc.
5. Air pressure when spraying is too low.

Prevention

1. Make sure when applying proper gun settings, technique and air pressure is used. If the gun is held too close to the surface or the speed of the gun pass is too slow then sagging is more likely. Sagging is most likely on edges and uneven surfaces, (in flat areas heavy application can be tolerated a little better due to the space it has to flow out).
2. Use the correct thinner. Faster thinners can help reduce sagging but also can be more susceptible to “dry spray”, (see troubleshooting dry spray).
3. Spray booth should be 20-25 °C, make sure the surface is at this temperature too, (for example if a vehicle has come from outside into a warm booth the surface of the vehicle will not yet have achieved ambient temperature).
4. Make sure surfaces are properly cleaned and degreased.
5. Make sure air pressure is adequate for atomisation of the coating.

Rectification

There are different cures for sagging dependant on the paint system chosen by the applicator. For synthetics such as our C71 Speedline and Coach Enamel sagging should be brushed out it occurs. If the sagging is not brushed out the synthetic will dry very, very slowly.

In other systems such as some two packs, cellulose and some acrylics flatting and polishing can rectify the problem.

The final option is sand to a smooth finish and refinish.