Paint Defects Manual (9)
Textured paint surface with uneven wave type formation that occurs when the paint surface dries faster than the substrate coats. This problem only occurs in the presence of synthetic enamels.
Synthetic Enamel applied too thick.
Little or no drier solution added.
Unfavourable drying conditions (e.g. shop temperature too high).
HOW TO AVOID
Keep to recommended number of coats and film build.
Ensure drier solution is added as part of the mixing formulation.
Ensure correct drying conditions (not too warm).
HOW TO REPAIR
For minor faults, dry the surface thoroughly, sand back to a hardened layer and then refinish. For severe wrinkling faults, strip the entire paint layers with paint stripper or by mechanical bead blasting and refinish to specification.
Water Spotting normally appears as light, whitish circular spots on the paint surface caused by the drying of a solution of water combined with mineral salts. The inner areas are normally intact, whilst the outer edge are often slightly raised.
Insufficient drying of fresh paintwork prior to being left in the rain.
Poor drying of paint due to thick coat application.
Incorrect hardener or quantity of hardener.
HOW TO AVOID
Ensure all fresh paints are applied using correct hardener, correct mixing ratio and the number of coats (film thickness) is correct and not excessive.
HOW TO REPAIR
If the damage is minor, first try washing with clean water; if this does not cure the problem polish with a fine polishing paste and finish with any standard deep gloss polish. For severe damage, sand the surface, ensure it is thoroughly cured and repaint.
43.Yellowlng of Clear Coat
Clear coat has a yellow hue to it.
Contaminated mixing equipment.
Defective clear coat or/and hardener.
Clear coat too thin.
Contaminated hardener, no cross link.
Defective clear coat.
Influence of corrosive conditions.
HOW TO AVOID
Ensure lids are tightly replaced after using hardeners.
Follow recommendations per Technical Data Sheets.
Use recommended hardener.
HOW TO REPAIR
Allow the finish properly dry. Sand and repaint.
44.PAINT DAMAGE IDENTIFICATION WITH THE SAND THROUGH METHOD
The sand through method is a simple way to diagnose paint damage more accurately on site and therefore determine the best repair method required. The various layers and products used, are carefully sanded through in one bad area back to the bare substrate (metal or plastic etc.) This allows all of the coats and layers to be clearly identified, their individual film thickness assessed and the fault to be highlighted. The sand through is best carried out by first sanding with P240 back to the substrate. The second stage is to re-sand the same area with as fine a paper as practical (e.g. P600). Finally the area could be polished with a fine polishing paste in order to allow to clear and precise observation of the coats and the problem. The following types of paint damage can be easily assessed using this method.
Blistering (see also Chapter "Blistering"). Blisters are easily detected, showing as different coloured spots as the top coat is removed revealing the layer below.
Crazing (see also Chapter "Crazing"). The depth of a crack in the paint layers can easily be detected in the sanded through areas. To assist even further, wipe Guide Coat into the cracks and allow to dry before sanding and the contrast will ease the identification.
Solvent Boil (see also Chapter "Solvent Boil"). This type of defect is often mistaken for dirt inclusions because of the small size of the defect. By sanding through, the defect can be easily identified as small cavities in the layer concerned.
Cratering (see also Chapter "Cratering"). Cratering shows as the flat recess or dimple in old paintwork, or on the surface of new paintwork and can indicate a poor flow characteristic of the paint.
Pinholing (see also Chapter "Pinholing"). Pinholes will appear as small dots of a different colour than the top-coat and originate from faults such as bubbles or pores in the substrate.
Swirl Marks/Swelling. Swirl marks will appear as colour filled lines in the primer or surfacer in the sanded through layer. The pattern and size of the lines will indicate the method of sanding used (hand or machine) and the grit size of paper used.
Number of Paint Layers of the Old Paintwork. The layers of paint, like the rings in a tree trunk, are exposed by sanding. With this method it is possible to say exactly how many coats of paint have been applied to the car and whether the risk of overloading on repainting is possible.
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 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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