Sanding Marks

Definition

Sanding swirl marks in the substrate show as lines in the top-coat.

Causes

1] The substrate was sanded with an abrasive that was too coarse.  The depth of the scratch is too deep for the subsequent products to fill and hide.

2] The correct drying times for the primer or surfacer coats were not observed correctly. The swirl marks from the sanding operation are clearly visible due to the swelling of the primer at the time of painting and the shrinkage on drying.

3] Filler coats were applied too thin to cover the sanding marks in the substrate.

4] Poor sanding technique and/or sanding machine.

How to avoid

1] Use specified grade of sanding disc and/or paper (e.g. for stoppers use P80/P150, primer filler/filler P240 – refer to relevant tech data sheets).

2] Dry as per specification.

3] Observe specified film builds.

4] Always place sanding machine on surface of paintwork before starting the machine.  For dry sanding of primer/filler coats, the eccentric stroke should not be greater than 5mm.

Repair

Sand out the scratches and refinish with correct filler coat and/or top-coats as necessary.