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A Case of Blushing in a Cherry Cabinet
Question
Forum Responses
From contributor B: You said "oiled cherry". Did you apply an oil on the wood before you did the sealer? From Paul Snyder, forum technical advisor: Good example of blushing. When the solvents in the lacquer quickly evaporate, it cools the surface. Put a little alcohol on the back of your hand and let it evaporate; it'll feel cold. If the dew point is close to the ambient temperature, the cooling effect of the evaporating solvents causes condensation (dew) to form and it gets trapped in the finish. The moisture turns the finish milky. I'd also use a little retarder to avoid the problem or wait until the humidity goes down, or turn up the heat in your shop and warm up the pieces you're spraying. With any of these fixes, the next coat should take care of the problem.
From the original questioner: Thanks for the input. I will try the remedies. What would happen if the lacquer was heated prior to application? Would this help to avoid this in the future? My shop is difficult to heat - it just doesn't stay around very long. Also, why did it blush only around the openings and not over the whole piece? Yes, oiled prior to sealer coat and cured for about a week.
From Paul Snyder, forum technical advisor: Heating your lacquer can make it worse. That'll increase the temperature difference. It's the temperature of the piece you're spraying that counts. A radiant heating system that keeps solid objects warm is an option you may want to look into. If heating isn't an option, then just use the minimum amount of retarder needed to cure the problem. It depends on the lacquer, but I can usually get by with 2% retarder and go up to 5% when the humidity is really high. It's pretty normal to see blushing concentrated at edges and corners. Seems to be the way the air moves over a piece as it's drying and the evaporating solvents create their own air movement. I've had pieces blush just on an end where they were exposed to moving air (air flow into the booth).
From contributor R: It may be caused by a different sanding grit. If the edges were sanded with a coarser grit paper or the flat surface was not sanded as much as the corners, this could contribute to a different evaporation rate. Also, the finish thickness is different on the corners than the flat area. The will also give it a different evaporation rate. From contributor D: We have had similar results with oils on wood. Cure was to dry the oil for up to two days. Oil that penetrates is not drying and causes the sealer not to bind. You could be seeing a delamination. Try scraping the area with even a fingernail. If it strips easily, your sealer has not bonded. From contributor V: The reason corners and edges would be more prone to blush is because they cool down faster than interior areas. On an edge, there is twice as much surface area in relation to the volume of wood, and thus a much greater cooling effect. Of course, air flow will also have a large effect. The same principle applies to the charcoal in your grill, and the steak on your plate. The edges cool quickest. Would you like to add information to this article? Interested in writing or submitting an article? Have a question about this article? Have you reviewed the related Knowledge Base areas below? 
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