How to Fix Sags in Metallic Auto Paint

Runs and sags in auto body paintwork are caused by the excess application of paint or clear coats. With clear coats, these imperfections can be easily sanded out and buffed back to a high gloss finish. However, runs and sags in metallic paints present a host of difficulties and an effective rectification will depend on the type of paint being used. A sag in solvent-based metallic material can be rectified prior to clear coat application. Unfortunately, water-based products will usually have to be repainted.

Instructions

Solvent-Based Metallic

1

As soon as a run appears during the painting process, stop applying more material and leave the paint to dry completely. Do not apply clear coat over sags in solvent-based metallic paintwork or the vehicle will have to be painted again.

2

Take a piece of P1500-grit wet-and-dry paper and dampen it with water. Do not use coarse papers as these will scratch the paint and tear it from the panel. Wrap the damp paper around a sanding block and place the largest flat area over the sag.

3

Work the sanding block in a circular motion, adding more water whenever necessary to stop the paper clogging, until the sag has been removed. Dry the panel thoroughly with a chamois leather and use an air blower to chase water from masking tape edges and apertures.

4

Apply two light coats of aerosol one-pack primer over the flatted area. Do not apply a full coat as this can cause a reaction that will result in the feathered edges of the sag wrinkling. Leave the primer to dry for fifteen minutes and rub over it lightly with a fine grade soft sanding pad. Once the primer has been keyed, wipe off the panel with a tack cloth to remove all traces of dust.

5

Continue to paint the vehicle in normal fashion by reapplying the metallic base coat, making sure that visual checks are carried out for further runs or sags before the clear coat is applied.

Water-Based Metallic

6

When a sag appears in water-based material, let it dry completely. Do not attempt to rub out the sag with wet-and-dry paper as this will cause the material to tear.

7

Once the water-based metallic material is dry, apply two full coats of clear coat to seal in the sag and leave it to dry overnight. If the sag is quite heavy, an additional layer of clear coat over the affected area must be added.

8

Take a sheet of P1500-grit wet-and-dry paper and flat out the sag, using water as a lubricant. Avoid burning through the clear coat when rubbing otherwise the water-based material will be exposed and this will lead to a chemical reaction when fresh paint is applied. The additional clear coat should help to stop this happening and will help to produce a perfectly flat finish..

9

Once the sag has been removed, dry off the panel thoroughly and blow excess water out of moldings and apertures with a blower. Repair any damage in the masking with tape and paper before continuing to avoid the risk of over-spray.

10

Wipe the vehicle with a tack cloth to remove any remaining traces of dust or fibers and apply fresh water-based metallic material to the vehicle. Continue checking the paintwork between coats for any further signs of running or sagging.