A coating that performs perfectly in a laboratory and a coating that performs perfectly in your spray booth are two different things. The gap between them is usually application, not chemistry.

The useful thing about coating defects is that they are diagnosable. Each one points to something specific that went wrong, and once you can read the symptom you can usually fix the cause the same day.

The eight you will meet most often

Blistering

Small raised bubbles in the film. Almost always moisture, either in the air or in the timber. Avoid coating in humid conditions and allow proper drying between coats.

Cracking

The film splits as it cures, usually because it was applied too thickly and the surface dried before the body of the coat did. Apply thin coats and follow the drying guidelines rather than the clock on the wall.

Peeling and flaking

The coating is not bonded to what is underneath it. Check your sanding, and check the moisture content of the wood. A surface that is too smooth, too dusty or too wet will not hold a film.

Orange peel

A dimpled texture like the skin of an orange. This is a spray problem: either the technique or the viscosity. Correct the viscosity first, because it is the easier variable to control.

Fish eyes

Small circular craters where the coating pulls away from a contaminant. Silicone, oil and wax are the usual culprits. Clean thoroughly, and check that the products you are layering are actually compatible with each other.

Blushing, or white haze

A milky cast in the film, caused by moisture trapping as solvent evaporates too quickly. Improve ventilation and switch to a slow-drying solvent. This is the classic monsoon defect.

Sags and runs

Gravity winning. Too much material in one pass, or the gun held too close. Thinner coats, correct distance.

Stain bleed

Colour rising through the topcoat after it has been applied. Use a pre-stain conditioner, and always test on an offcut before committing a full batch. On mango and acacia this is often tannin rather than stain, which needs a tannin blocker rather than a conditioner.

The pattern underneath

Look at that list again and a pattern emerges. Almost every entry comes back to one of three things: surface preparation, application technique, or the conditions in the booth on the day.

Very few coating failures are caused by the coating. That is worth remembering the next time a batch goes wrong, because it changes where you look first, and it usually means the fix is free.

It is also why our technicians spend so much time on factory floors rather than on the phone. Most of these are visible within ten minutes of watching a line run.