Typical Spray Applications Problems and Solutions
Blushing
Often caused by rapid surface drying in high humidity and entrapment of moisture within the film.
Lacquer Thinners, being a compound mixture of various solvents, will often cause the lacquer to blush or bloom under certain atmospheric conditions. The addition of retarder thinner or a slow drying solvent can rectify blushing. It is always worth while purchasing quality thinner, as cheaper grades tend to be troublesome. Occasionally water in the airline, caused by the water and oil separator not functioning properly, may cause a bloom. This can be remedied by dismantling and thoroughly cleaning the separator, as well as cleaning the airline
Blisters
These are generally caused by either (A) a solvent imbalance, force drying the coating, causing the surface to dry too fast before the air and solvent has time to escape from the coating, or (B) moisture being sealed beneath the paint film. Also lack of adhesion caused by oil on the surface probably from dirty hands.
Avoid touching panels prepared for lacquering. Where it is necessary to touch a panel to remove any foreign matter it should be done with a clean rag or better still a tack rag. Be sure all water has been dried off the job, blown out of cracks and from behind mouldings.
Cracking
Similar to checking but the cracks are much deeper and may penetrate the sealer or even to the timber. The application of heavy successive coats, without allowing ample drying time between coats can also be a major cause of cracking. Inferior grades of timber or timber that is not properly dried can sometimes shrink and may also cause the surface coating to crack.
Orange Peel
This term is self explanatory. It refers to a finish, which has a texture resembling the skin of an orange. While orange peel is not altogether detrimental to a job, first class work demands that a job be free from orange peel. Too much air as well as being too close to the job while spraying, is one of the main causes. Material too thick, use of too quick-drying a thinner, are also causes. Spend a little care in properly adjusting the gun. The use of retarder thinner will also help the material flow.
Roughness & Dryness
This is caused in a surface by not applying wet coats. The surface must be closely watched while spraying so that the lacquer can be applied in wet flowing coats. Dryness usually occurs in different corners and parts where it is hard to direct the full flow of the spray.
Peeling
This results nearly always from poor adhesion, which can usually be trace to faulty cleaning, poor preparation and not sanding between coats. Recoating over a surface that has been waxed will result in peeling. Care should be taken to remove all traces of wax.
Curdling
This usually occurs when the material is being mixed. It can be caused by cheaper grades of thinner not having enough solvent content or incompatible grades of thinner being mixed. As a rule if using a quality lacquer be sure to use a quality thinner if it is required. Solvents which can cause Curdling: Mineral Turps, Enamel Thinner, Spray Stain Reducer and PWS Reducer along with petrol etc could all cause this problem.
Streaks
Streaks are usually caused by the operator not lapping each stroke perfectly. It is not always sufficient just to lap the fan stroke an inch or so. It may be necessary to lap half the width of the fan shaped spray.