Craters

Craters are small circular indentations or depressions on the paint surface.  The crater edges are often slightly raised with depressed, flat centers.  These circular defects typically range in diameter from about 0.5 to 3 mm. The defect may range in appearance from a very flat shallow recess in the clearcoat to a deep fault which extends all the way to a lower paint layer. They can often be observed in the wet paint but are most troublesome as defects in the baked paint.  Craters can be observed in all layers-clearcoat, basecoat, or primer. Craters can be classified by type based the depth of the defect depression: Type A=basecoat exposed; Type B=clearcoat exposed, Type C = substrate exposed

Also known as: Cissing, Fisheyes, saucering

Craters are normally caused by a low surface tension contaminate.  The contamination source can be in the paint or from the paint shop environment-equipment or personel.  This contaminate when present on a substrate produces a surface tension gradient that causes the paint to flow away from the low surface tension contamination area, resulting in the circular crater defect.  The contaminate can be a liquid or solid present on the substrate and the crater begins to form most often directly after wet application of the paint layer.  Only very small amounts of the low surface tension material contamination are needed to form the crater defects.  

Since the presence of very small amounts of low surface tension contaminants can cause crater defects great efforts must be taken to avoid introducing these materials into the painting process.  Typical known crater causing materials are silicones and other organic compounds like greases and some the fatty acid stearates.

Items 1-6 list possible sources of cratering to avoid. Consequently, various tips and preventive measures to eliminate cratering can be established. As a basic principle, it is best to use silicone-free products in paint shops and practice good housekeeping.

1.Humans – contaminated working clothes, rubber gloves, skin and hair care products, antiperspirants, silicone wristbands -like yellow Livestrong™

2.Spraybooth – lubricants from moving parts, mould-release agents from plastic add-on parts, hoses and sealing compounds, poorly cleaned oil and waste water separators, dirty air filters in ceiling and floor

3.Paint materials – incorrect use of additives, impurities in the coating due to deficiencies in manufacturing, packaging, transport and storage

4.Workpiece – residues from mould-release agents on plastic parts, residual drawing agents and lubricants, soldering pastes, bitumen and oil from insulating mats

5.Painting process additives – mould-release agents from new sponge cloths, unsuitable cleaning agents and cloths, unsuitable sanding materials (scouring cleaners and sand paper containing stearates), adhesive from adhesive tapes

6.Environment – aspiration of contaminated air (polishing agent, silicone spray, fine dust, etc.) from other parts of the bodyshop, seals and insulating materials from the building

• Consult your specific paint shop procedures.
• Finesse Deck:  Sand plus 2-step Polish
• Spot Repair:  Sand plus Repaint