Even experienced finishers encounter problems. The good news is that most guitar finishing defects are fixable if you know what caused them. This guide covers the most common issues you will encounter when spraying nitrocellulose lacquer and other guitar finishes.
Blushing (blooming)
Blushing appears as a milky-white cloudiness in the lacquer, usually within minutes of spraying. It is caused by moisture becoming trapped in the finish — water vapour from humid air condenses in the film as the solvents evaporate and cool the surface.
Fix: Light blushing often clears as the lacquer cures. If it persists, mist a very light coat of cellulose thinners over the affected area — the fresh solvent re-opens the surface and allows trapped moisture to escape. For severe cases, sand back and re-spray in drier conditions.
Prevention: Spray below 65% relative humidity. In humid weather, add retarder thinner to the lacquer to slow evaporation.
Orange peel
A textured surface resembling orange skin, caused by the lacquer not levelling before it starts to set.
Fix: Mild orange peel can be level-sanded out once fully cured — 800-grit through 2000, then polishing compound. Severe cases need sanding back and re-spraying.
Prevention: Spray above 18°C. Thin the lacquer slightly if viscous. Hold the gun 15-20cm from the surface. Spray light, overlapping passes.
Runs and sags
Drips or curtains that form when too much material hits a vertical surface.
Fix: If caught within seconds, a light mist pass can re-wet and level the area. Otherwise, let it cure completely, slice the bulk off with a razor blade held flat, and level-sand smooth.
Prevention: Thinner coats. Consistent spray speed. Keep the nozzle perpendicular to the surface. Watch edges, curves and lower portions of vertical surfaces.
Fish eyes
Small circular craters where the lacquer pulls away from the surface, caused by silicone contamination from furniture polishes, hand creams or workshop sprays.
Fix: Sand back, clean the entire surface thoroughly with naphtha, and re-spray. A fish-eye eliminator additive can be mixed into the lacquer for persistent contamination.
Prevention: Keep silicone products out of your spray area. Clean the workpiece with naphtha before spraying. Wear clean gloves between coats.
Lifting
New lacquer wrinkles, bubbles or peels the coat underneath. This happens when solvents are too aggressive for the underlying layer — most often when spraying nitro over polyurethane or an unknown existing finish.
Fix: Stop spraying. Let everything dry, sand back to a stable layer and start again. If the underlying finish is incompatible, strip to bare wood.
Prevention: Test compatibility on an inconspicuous area. Never spray nitro over poly or polyester. When re-finishing with an unknown existing finish, strip to bare wood.
Solvent pop
Tiny pinholes in the surface, visible after level-sanding. Caused by solvent vapour escaping through the film after the surface has skinned over.
Fix: Light cases can be filled with additional thin coats and re-sanded. Severe cases need sanding back and re-spraying.
Prevention: Thinner coats with adequate flash-off time between passes. Avoid spraying on hot surfaces or in direct sunlight.
Witness lines
Visible ridges where a colour coat edge or masking line shows through the clear coats. Happens when clear is not thick enough to bury the underlying transition.
Fix: Apply more clear coats over the area, then level-sand flat.
Prevention: Apply 8-10 minimum clear coats over colour transitions. Allow full cure before level-sanding — lacquer shrinks as it cures and buried edges can reappear.
Sanding through colour
Level-sanding cuts through the clear coats into the colour underneath, exposing the base colour or bare wood. The most common place for this is on edges and curves where the finish is naturally thinner.
Fix: If caught early, re-spray additional clear coats over the entire panel and re-sand. If the colour has been fully removed in a spot, you may need to re-mask and re-spray the colour before rebuilding the clear.
Prevention: Sand flat areas only — avoid pressure on edges. Use a flat sanding block rather than finger pressure (fingers wrap around edges and concentrate pressure). Apply extra clear coats over edges before level-sanding.
