Advice on paint defects
Solvent Test
Before starting any repair painting, we recommend that a solvent test is carried out on a sanded area to reveal any layers (coats) which may be solvent sensitive and therefore require special attention or treatment to avoid problems.
Solvent-sensitive layers may be:
- TPA (Thermo Plastic Acrylic)Paintwork.
- Nitro-Cellulose Paintwork
- Non-cured Synthetic Enamels.
- Sensitive/Swelling Works applied Paintwork..
How to Test:
After sanding, soak a piece of cloth in a strong thinner (e.g. 352-50 or 352-91) and rub over the sanded area. Watch closely for any signs of a reaction i.e. if one or more of the layers swells, lifts, rivels or goes sticky then it is solvent sensitive.. Having established that the coat is sensitive the correct method of repairing is essential to avoid problems.
When repairing such layers (coats), note the following:
- sanding process should be finer and cover a wider area than normal.
- Do not use any polyester filler over the feathered edge, leave bright metal showing between.
- apply filler/surfacer and top-coats only in thin light coats and allow good flash-off times between coats.
- do not use a wet-on-wet surfacer or system.
- carefully dry with IR heaters (not over TPA substrates)
- only use a suitable finishing process
- where sensitive coats are found along with a high film build, strip back to bare metal.
- paint system layers that prove to be extremely sensitive to solvents must be removed before any repair work is done.
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