Finish appearance issues and how to solve them
April 13, 2020 | 9:51 am CDT

Successful application of high-performance coatings can be challenging. To overcome these challenges, the application technician must exercise rigorous control over the multiple conditions that come into play during the preparation and the application of wood finishes.

For optimum quality and results, a dust-free environment, without major variations in temperature and humidity, is critical. Equally important is the surface preparation of the substrate, the compatibility of multiple coatings, settings and adjustment of the finishing application equipment, and the drying time.

Despite best efforts, problems can result. What follows are some common issues, possible causes and solutions.

Problem: Orange peel: A pebbled surface similar to that of an orange skin. Caused by coating not leveling out completely after application by spraying.
Causes: 1) The product is insufficiently diluted. 2) The air output from the spray gun is too high. 3) The product is drying too rapidly.
Solutions: 1) Adjust the viscosity of the coating. 2) If the viscosity is OK and the problem persists, use a retardant. This will increase the drying time and give the coating sufficient time to spread evenly.

Problem: Fish eyes: The appearance of small craters in the finish of a coated product.
Causes: The product is contaminated by silicone (from the worktable), oil (from the compressor) or water in the line. It is also possible that the item to be coated is already contaminated by wax or other substance contained in the varnish remover.
Solutions: 1) Find and eliminate the source of contamination. 2) Use a leveling agent.

Problem: Pinholes: The appearance of tiny holes without coating.
Causes: 1) An excessive thickness of coating. 2) Drying too fast. 3) Improper spraying.
Solutions: 1) Apply thinner coats. 2) Use a retardant. 3) Adjust the spray equipment nozzles.

Problem: Blooming: A bluish cast which forms on the surface of a dried film of finishing material.
Cause: May be caused by a deposition of smoke or other foreign material from the atmosphere or by the softening of the film during rubbing operations.
Solution: Identify cause and correct it.

Problem: Blushing: Film defect that appears as a milky opalescence as the film dries.
Causes: 1) Excessive humidity. 2) Improper balance of solvents in the film.
Solution: Adding 3-5% of retardant to the lacquer generally solves the problem.

Problem: Cracking: The appearance of surface or in-depth cracks in the film.
Cause: The final coat too thick.
Solution: Follow application instructions.

Problem: Lifting: The softening and raising or wrinkling of a previous coat by the application of an additional coating; often caused by the solvents.
Causes: 1) The base coat is sensitive to the solvent or insufficiently hardened. 2) The solvent is too harsh. 3) Sanding through the sealer coat. 4) Too many coats. 5) Humidity is too high.
Solution: Use the proper system and avoid applying thick coats.

Problem: Color problems: The final color is different from the reference sample.
Causes: 1) Improper mix. 2) Inadequate sanding. 3) High humidity. 4) The application is too dry or too wet.
Solutions: 1) Mix thoroughly. 2) Ensure proper sanding. 3) Use adequate spraying pressure.

Problem: Uneven fill: There’s uneven fill of the surface imperfections.
Causes: 1) Improper sanding or the veneer is too porous. 2) The coating is fast-acting.
Solutions: 1) Ensure the base coat has hardened before sanding. 2) Use nitrovinyl base coats.

Problem: Bubbles: The appearance of bubbles in the film during or after drying.
Causes: 1) Veneer is too porous. 2) Open-grain wood. 3) Drying too fast.
Solutions: 1) Use a product specifically for porous surfaces. 2) Use a retardant or bubble eliminator.

Problem: Running: Traces left on the surface by a coating that ran.
Causes: 1) Excessive thickness of coat(s). 2) Thinner is too slow. 3) Temperature is too cold. 4) The spray is too coarse.
Solutions: 1) Apply thinner coats. 2) Use the correct thinner for the application. 3) Adjust the spray equipment.

Problem: Fumes: The appearance of fine surface droplets after drying.
Causes: 1) Drying too fast for a large surface. 2) The spraying equipment is delivering too much air.
Solutions: 1) Use a retardant to slow down drying. 2) Adjust the spraying equipment.

Problem: Improper spreading: The coating does not cover evenly.
Causes: 1) The coating has been insufficiently reduced. 2) Evaporation is too quick. 3) Improper spraying. 4) The coat is too thin. 5) A draft is causing a temperature variation.
Solutions: 1) Dilute the product as per instructions. 2) Use a thinner that will evaporate slower.
3) Adjust the spraying equipment. 4) Apply a wet coat. 5) Eliminate drafts.

Problem: Slow drying or insufficient hardness.
Causes: 1) Too humid or too cold in the paint shop. 2) Migration of coating into the wood. 3) The coating batch is past due. 4) An excessive thickness of coat. 5) Improper catalyzation.
Solutions: 1) Maintain proper temperature and humidity levels. 2) Use an insulator to avoid migration. 3) Use a fresh batch of coating and apply the appropriate thickness.

Problem: Low adhesion: The coating rubs off or is less resistant than normal.
Causes: 1) Greasy surface. 2) The sanding is too fine. 3) Defective system.
Solutions: 1) Clean the surface. 2) Sand with 120 grit paper. 3) Contact your representative for recommendations regarding your system.

Source: Canlak. For more information call 819-367-2201 or 888-806-2366, or visit

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