Coating defect

Brush marks

Lines of ridges and furrows that follow the brush; very coarse ones are called ropiness.

Brush marks: the surface as you see it, and a schematic cross-section.

Causes

Paint too thick for brushing, or the wrong thinner.
Brushing back into paint that has started to set.
A hot surface or the wrong brush.
A coating that levels poorly, applied by brush where the data sheet expects spray.

Prevention

Bring the paint to brushing viscosity with the recommended thinner.
Finish with light strokes in one direction and do not rework setting paint.

How it is assessed

Visual, most visible on gloss finishes; check the film thickness in the furrows.

Telling it apart

Orange peel: Orange peel is an even, random dimpling from spraying. Brush marks run in lines that follow the strokes.
Runs and sags: Runs and sags hang downwards where too much paint flowed. Brush marks are ridges where the paint did not flow out enough.

Repair

Sand smooth and apply another coat. The specification and the coating manufacturer have the final word on the repair procedure.

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About this page

Written from coating practice and the published rating standards, in our own words; the drawing is schematic. Checked on 2026-10-14; errors go in the corrections log. CoatMentor is an independent study aid. It is not affiliated with ISO, AMPP, SSPC, NACE International, ASTM or FROSIO.