During paint inspections, our surveyors see a lot of paint defects passing by. In this article we explain the defects ‘Runs, sags and curtains’.
Runs, sags and curtains are the downwards movement of paint that can appear shortly after the application and before the setting of the paint. Sagging is usually apparent on local areas of a vertical or curved surface. When sagging occurs over a long distance this is described as a curtain. If the wet film thickness is much too high, excessive sagging can result in pools of paints forming on horizontal surfaces or in corners which could resulting in cracks after curing.
Paint defect – curtain of paint
- Paint was applied in excess of the dry film thickness specified
- Excessive or improper reducer/thinner had been added to the paint
- Various components have been improperly mixed
- Incorrect or a lack of curing agent had been used
- The object being painted was too cold
- Improper spraying technique was used, such as but not limited to:
- Spray gun was held to close to the surface
- Too much pressure on the pot or gun
- Dirty air cap
- Inconsistent movements
- Pot life of catalysed material has been exceeded
- If occurred in extreme circumstances it could be a formulation problem.
Extreme sagging occur when paints have been applied in coats which are too heavy and is commonly a result of wrong application technique (overlapping) or too short recoating interval.
- Use a smaller nozzle or adjust spraying technique
- Use lesser amount and or faster solvent
- Check application instructions and improve the climatically conditions
- Materials should be mixed in accordance with the application instructions
- Improve the spraying technique. Use the right distance of 20-25 cm from object and nozzle and a right angle to the surface. Use a 50% overlap with each pass per application.
- If sagging is noticed at the spraying stage, it could be brushed out while the paint is still wet. It should be noted that this may not result into an acceptable appearance.
- When the paint has dried, abrade and clean defected areas and re-shoot the surface. In some cases spot repair could be allowed.
- Small runs and sags might in certain circumstances be acceptable and should be defined in the contract.
Note: Buffing and/or polishing of a polyester – urethane finish is generally not accepted and will only be accepted for very small areas after consultation and written approval of the owner’s representative.
Due to the remedies before mentioned, you are able to prevent runs, sags and curtains. The CCS surveyors are more than happy to advise you or assist you with the solutions.