Top 8 finishing challenges & solutions

Photo By Gemini Coatings

Wood finishing is both an art and a science. The finish of furniture, cabinetry, architectural millwork, or any wood surface not only protects the material but also enhances the design and overall aesthetic. The wood finish is often the first thing seen, so correcting inconsistencies is crucial. Use the following tips when solving issues that can occur in the wood finishing process.  

1. Adhesion: The coating is chipping or is easily scratched or rubbed off of the surface.
Possible causes: Improper sanding of white wood or insufficient sanding between coats; too much stain or glaze left on the surface; improper drying between recoating; fast drying causing the stain or coating to sit on top of the wood rather than properly penetrating or incompatible products used. 
Countermeasures: Make sure the raw wood is not over-sanded or polished, and use sandpaper no finer than 150 grit. Sanding between coats should be completed just before applying the next coat with paper no finer than 320 grit. Wiping stains should be wiped clean with all excess stain removed and 90-95% of glaze should be removed. Follow the dry times listed on the Product Data Sheet. Slow the dry time of the coating by using a recommended retarder. Stick with the manufacturer's recommended system.

2. Acid bloom: A hazy, greasy film forms on the surface of a finish. It typically has an unpleasant, acidic odor, and the hazy appearance returns if wiped clean. 
Possible cause: Too much catalyst has been added to the coating. 
Countermeasure: This issue requires the parts to be stripped and refinished.

3.  Cracking: Cracks that go across the grain are usually called “cold checking,” typically occurring when more than the recommended number of coats is applied. Smaller or spiderweb cracks typically appear when a product has been over-catalyzed or has not cured correctly.  
Possible causes: Too many coats; too much catalyst; heavy application; poor inter-coat adhesion or the catalyzed product was subjected to extreme cold temperatures before curing completely. 
Countermeasures: Strip and refinish parts that have cracked and apply only the recommended number of coats. Apply the product only at the recommended wet film thickness listed and let it dry per the recommendations on the Product Data Sheet. Make sure each coat is sanded properly with the recommended type and grit of sandpaper. Catalyzed products should cure at a minimum of 65°F for at least a week before being transported in cold temperatures.

4. Fisheyes: Craters occur when the coating is not able to wet the substrate completely, often due to contamination. 
Possible causes: The surface may be contaminated by silicone, overspray dust, grease or water; the air supply to the air gun or to clean parts may be contaminated by oil, water, etc. or airborne contaminants such as aerosol saw blade lubricants, waxes or cleaning supplies.  
Countermeasures: Make sure the surface is free of contaminants. Make sure any compressors supplying air are drained regularly and make sure good quality air regulators and filters are installed in the air line. Avoid using lotions, aerosol products or consuming greasy foods in or near the finish room.

5.  Bubbles, microbubbles and blisters: Bubbles are visible and break the surface in the dried film. When the bubbles are very small and trapped beneath the coating’s surface, they are referred to as microfoam or microbubbles. Blisters are much larger.
Possible causes: Too much coating has been applied; coating has become high in viscosity due to solvent loss or cool temperatures; too much air movement in the finish/drying area; ambient temperature is very hot; incorrect thinner used; leak in siphon hose/tube to a high-pressure spray unit or veneer issues. 
Countermeasures: Follow wet mil recommendations on the Product Data Sheet. Use a wet mil gauge to measure the amount of product being applied. Reduce with the recommended thinner to correct application viscosity listed on the Product Data Sheet. Warm the product to 78°F. Eliminate air movement. Move parts to an area with less air movement or flash off. Add recommended retarder to slow flash and dry times. Replace siphon tube/hose. Try applying a very light (1-1.5 mil) dust coat and let dry to touch and then apply a normal coat.

6. Blushing/moisture blush: The surface of the coating has a milky appearance or has turned completely white. 
Possible causes: Spraying when relative humidity is high or the product has been thinned with a solvent that is too fast. 
Countermeasures: Add the recommended retarder before spraying to avoid the blush. To fix a blushed piece, add the recommended retarder to the coating, scuff sand the piece, and re-spray. The retarder may also be sprayed directly on the blushed surface.

7.  Lifting or wrinkling: Small wrinkled or puckered areas on the coating surface that look similar to a crack and has pronounced raised edges.
Possible causes: Under-cured coating due to heavy application of previous coat; insufficient curing temperatures; excessive slow solvent added or incorrect catalyst amount; coating was applied over a wet stain or glaze; poor inter-coat adhesion or incompatible products in the system. 
Countermeasures: Make sure the correct catalyst and amounts are used. Wait 48 hours and try re-coating again. Ensure that curing temperatures are adequate, ideally at least 77°F. Make sure the surface is scuff sanded sufficiently and only just before the next coat is applied. Do not mix systems, such as using a conventional lacquer sealer being applied under a conversion varnish.

8.  Orange peel or texture: The surface is rough or textured like the surface of an orange.
Possible causes: The viscosity is too high due to solvent evaporation or coating that is cold; fast dry; substrate temperature and coating temperature are significantly different or improper spray technique- too fast, gun held too far away or improper equipment set up.
Countermeasures: Add the recommended thinner until the correct viscosity is achieved. Add the recommended retarder to slow the dry time. Warm the coating and warm the substrate until the temperature of each is relatively equal and as close to 77°F as possible. Make sure the spray gun is held 6-8 inches away and slow down if necessary. Make sure each pass is overlapped at least 50% into the previous pass. Check equipment settings and make sure there is not too much atomizing air and that the fluid pressures are sufficient. This will vary with each type of equipment. 

Source: Gemini Coatings. For information on Gemini, call 800-262-5710 or visit


Have something to say? Share your thoughts with us in the comments below.