Technology Transfer Network - Air Toxics Web Site
Waterborne Wood Coatings
Converting to waterborne coatings generally is a less costly method of reducing VOC/HAP emissions than converting to UV-cured or powder coatings, and, therefore, is appealing to smaller shops. Capital investment ranges from nominal to several thousand dollars to purchase stainless steel lines and equipment. The average facility studied replaced several gun or pump components, but not the entire coating line. The cost of the waterborne coatings themselves tends to be higher per gallon than traditional solvent-borne coatings; however, many facilities found that the higher solids content of the waterborne coatings provided better coverage and resulted in the use of a smaller volume of coating per piece.
The appearance of products finished with waterborne coatings often is the main hurdle to overcome. Some facilities described pieces finished with waterborne stains as being "muddy," or lacking the "depth" of a typical solvent-borne stain. Pieces that receive only a sealer and/or topcoat may appear to have a green tint in the wood, instead of the amber tint associated with solvent-borne coatings. However, working with the coating supplier to adjust the coating formulation often solved any appearance issues.
Waterborne coatings generally are applied using spray guns, although dipping, roll coating, and wiping also are used. Application of waterborne coatings by spray gun requires a different operator technique than that used to apply solvent-borne coatings. Several facilities noted that it was easier to train an employee who had never sprayed coatings before than one who had sprayed solvent-borne coatings for years. The waterborne coatings often have to be applied sparingly to achieve the desired finish.
Another difficulty often associated with waterborne coatings is grain raise. The water in the coatings is absorbed by the wood, causing it to swell. Grain raise results in a finish that has a rougher feel and appearance. However, most facilities have found that, with the proper combination of coatings, equipment, and sanding, grain raise can be minimized to an acceptable level. Some facilities chose to use only a waterborne topcoat instead of a full waterborne system (waterborne stain, sealer, and topcoat).
Waterborne coatings often require a longer drying time than typical solvent-borne coatings because the water in the coating does not evaporate as quickly as the solvent. Larger facilities often install ovens for use between coating steps to shorten drying times. Smaller facilities that use the same spray booth (with no oven) for each coating step, in more of a batch process, generally found that by the time they were ready to apply the next coating, or package the product, the piece was dry.
In addition to VOC and HAP reductions, the main advantages cited by facilities that have switched to waterborne coatings include:
- elimination of the odor associated with solvent-borne coatings;
- reduction of fire risks and associated ease of storage (an explosion-proof storage room is not required);
- low capital investment to convert from solvent-borne coatings;
- a more durable finish; and
- reductions in permit paperwork and/or fees.
This page was last modified on:June 01, 2000
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