Fish eyes, a run and two dull patches on one bonnet
A bonnet is refinished in a 2K base/clear system. After a 30-minute bake at 60°C the painter finds about a dozen crater-like fish eyes clustered in the centre of the bonnet, a 60 mm clearcoat run along the left edge, and two dull grey patches on the right side that look dry but feel slightly soft. The booth filters were changed last week, the compressed-air line has a new combined filter/regulator, and a technician had been using an aerosol tyre shine and dashboard dressing in the adjacent bay an hour earlier. The painter had wiped the panel with a new brand of wax and grease remover, tacked it, and sprayed base then clear with a 1.4 mm gun at 2.2 bar. The shop wants the car delivered tomorrow and the painter suggests flatting the defects, adding a fish-eye eliminator to the clear and recoating over the top.
1. Diagnose each defect and rank the likely sources.
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Fish eyes in the centre. Circular craters with raised rims show the clear pulled away from a low-energy contaminant. The clustered pattern points to contamination in the booth air or on the panel, not the clear itself. Ranked sources:
- Silicone from the aerosol tyre shine and dashboard dressing used next door. Silicone travels on air currents and settles on every surface, including inside a booth if doors were open.
- The new wax and grease remover, if it was not allowed to flash or if it is a slow-evaporating blend that was trapped under the base.
- Oil or water from the air line. A new filter/regulator can still pass moisture if the line was not blown out or the filter is undersized for the gun's demand.
New booth filters rule out dirty intake air as the main cause, but not airborne silicone.
Run on the left edge. Too much material per pass, gun too close or too slow, or hesitation on a vertical edge where film builds fastest. At 2.2 bar with a 1.4 mm tip, a slow pass on an edge runs readily.
Dull, soft right-side patches. These are solvent entrapment or die-back, not dry spray. Softness after a 60°C bake indicates under-cure or over-thinning; the dullness appears as solvent leaves the film. Cold or damp air at the gun gives a similar result. It will not polish out.
2. The painter proposes flatting, adding fish-eye eliminator and recoating. Explain why that is the wrong correction and describe the correct one.
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Fish-eye eliminator is essentially a silicone oil that lowers the paint's surface tension so it flows over contamination. The contaminant is still there, and the additive spreads through the gun, the booth and the next several jobs, making fish eyes more likely rather than less. It is a production crutch, not a repair.
Correct sequence:
- Find and eliminate the source first - the aerosol products, the air line, the wipe product. Recoating before this just repeats the defect.
- Strip the affected clear back to sound basecoat or primer. A crater that has cured into the film cannot be flatted out; the rim is a film thickness defect.
- Clean and tack the panel, and use only products already proven on this job.
- Seal the area with a fresh, uncontaminated sealer.
- Spray a test panel alongside the bonnet at the same time. If the test panel shows fish eyes, stop - the contamination is still present.
- Recoat base if the film was broken, then clear, in a clean booth, with a drained and filtered air line.
The run can be flatted and polished only if enough clear remains over it; if it is deep enough to break the film, the panel needs recoating. The dull soft patches must be cured correctly before any sanding, or they will return.
3. What would you change in the shop's practice to stop this recurring, and what would you check before promising tomorrow's delivery?
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Practice changes
- Ban silicone-containing aerosols and dressings from the paint area and the adjacent bays. Silicone contamination is a shop-wide problem, not a booth problem.
- Give the air line a proper coalescing filter and water trap, drain the compressor, and blow the line down before a job. A filter/regulator at the gun is the last defence, not the only one.
- Keep one gun for clear only, clean it in an enclosed washer, and never use reclaimed gun wash on a topcoat job.
- Train on flash times for wax and grease remover: wet is not the same as flashed.
- Keep a written booth log - filters, pressure balance, bake cycles, and any aerosol use nearby.
Before promising delivery
- Confirm the source has been found, not just guessed.
- Have a test panel sprayed alongside and inspected.
- Check the cure: the film should be hard and solvent-resistant before sanding and polishing, which means a bake and a cool-down, not a shortcut.
- Confirm the clear film build is enough to allow flatting without breaking through.
- Only then rebook the handover. A second failed delivery costs more than one day's delay.