Finishing materials: Problems & solutions

Example of blooming. Photo courtesy of Chemcraft.

Listed below are some common finishing problems and how to solve them.

Problem: Blisters/pinholes: Micro-bubbles or voids in the coating surface; unfilled pores on open grain wood/veneer. 
Solutions: Use a slower thinner if necessary; reduce the board temperature and minimize the applied film thickness; check the viscosity of the finish; ensure that the substrate is not porous; for open-grain woods use a filler or different primer.

Problem: Blooming: Hazy deposit on the film; oily or wax-like substance on the surface; reduced gloss; mottled or non-uniform surfaces.
Solutions: Adjust catalyst level – over–catalyzation; do not use stearated materials such as lacquers and certain polyesters under acid-catalyzed coatings; check the formula for incompatibility; check the substrate for contamination.

Problem: Brown spots in the film. 
Solutions: Clean the air lines of oil contamination; drain or repair the oil separator.

Problems: Bumps and sinks: uneven surface appearance; low depth of image (D.O.I.).
Solutions: Add silicone flow additive; add thixotrope.

Problem: Cracking: Cracks and checks in film.
Solutions: The applied coating is too thick (use wet mil gauge during application); reduce the moisture ratio; check the mixing ratio; check the suitability of the surface and coating; check the drying and storage conditions; check suitability of the surface and coating.

Problem: Cratering: Depressions in the finish with raised edges and material at the center.
Solutions: Clean the substrate and equipment before application; filter material; check/clean the air system and ventilation control; addition of silicone flow agent.

Problem: Crawling: Formation of beads, islands, craters or pinholes; poor wetting of the substrate.
Solutions: Clean the substrate before application; ensure sanding before application; addition of a silicone flow agent.

Problem: Discoloration: Change in the color of the finished parts; yellowing of film.
Solutions: Check the age of the coating; check contamination from drum liner; check iron or aluminum contamination from application equipment; check for the presence of foreign vapors or fumes; check to ensure the presence of UVA, if required; check to ensure the material is not stored at excessive heat; check for tannin bleed.

Problem: Flooding: Uniform color change; surface enrichment of one or more pigments; a different color on disturbed surface/rub-up.
Solutions: Reduce the  film thickness; raise the viscosity of the coating; speed drying.

Problem: Gloss variation: Uneven gloss areas; incorrect/unexpected gloss; flat or glossy spots.
Solutions: Ensure the correct drying or oven temperatures; ensure the correct film build; apply a seal coat to eliminate absorbent areas on the substrate; reduce the solvent strength to reduce exudation of resins from wood; ensure a clean substrate; addition of a silicone flow agent.

Problem: Gray pores: Gray areas in deep pores; poor cleaning of sanding dust from pores; poor wetting of pores.
Solutions: Blow out the sanding dust from the pores on sanded panels; reduce the viscosity of the sealer; add non-contaminating silicone to improve the wetting of sealer; change the sealer to improve wetting and shrink-back; change to urethane sealer.

Problem: Haze: Dulling of the finished surface; exudation to surface; fine solvent pops; microvoids; fine Bénard cells.
Solutions: Use the correct thinner; check current catalyzation; check the dryness of the previous coat; stir the material to ensure uniform product; use a retarder solvent.

Problem: Hiding: Poor coverage; show-through of dark lines at the edges of the profiles.
Solutions: Reduce the amount of the thinner in material; mix the material thoroughly before use; increase/ensure the correct film build; sand the sharp corners of profiles; increase the speed of the solvent balance.

Problem: Mud cracking: Fine cracks in the surface of the waterborne finish.
Solutions: Increase the temperature of the application area; increase the drying temperature; add a coalescing solvent under agitation; increase the substrate temperature.

Problem: Silking: Parallel lines of irregularities in the finish; floating problem; phase separation; specialized Bénard cells; incompatibility.
Solutions: Add dispersant; use a silicone additive; increase the application viscosity; add a thixotrope or thickener.

Problem: Solvent popping/pinholing: Formation of holes, craters, dimples, and volcano-like bumps; visual appearance of seeds; visual appearance of low gloss.
Solutions: Increase the flash time; use a retarder solvent; use a slower solvent blend.

Problem: Solvent trap: Cracking/crazing of the finish after unpacking; glossy or flat spot after stacking.
Solutions: Decrease or ensure the correct film application; ensure the correct air movement and dry times; do not store in a cold environment before the complete cure; increase the cure before stacking or packing; ensure correct catalyzation.

Problem: Tearing: Large cracks in the waterborne finish; uneven drying of the surface before the body of the paint film; poor through cure in waterborne materials.
Solutions: Decrease the surface heat to finish; increase the substrate temperature.

Problem: White spots or contamination in film.
Solutions: Ensure the flatting agent is completely mixed before application; filter the material before use; check water separator.

Additional troubleshooting tips courtesy of Chemcraft were included in last year's Red Book.

Source: Chemcraft/AkzoNobel. For information, call 336-841-5111 or visit More troubleshooting tips and videos online at Chemcraft.


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