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Expert's Corner — acetone

TIP: Finishing Oily Woods

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Many tropical woods, with the notable exception of mahogany, contain an oily resin that causes oil and varnish finishes to not dry well. The oily resin gets into the finish and keeps the finish molecules from hitting each other and crosslinking. The resin acts like paint thinner that doesn’t evaporate. Counter-intuitively, the oily resin usually doesn’t affect the drying of lacquers and water-based finishes. But in cases where the oiliness is severe, it could weaken the bond to the wood. The trick to finishing oily woods successfully is to remove the oil from the surface just before applying the finish....

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TIP: Removing Oil and Grease Stains

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If the oil or grease stain is fairly fresh on the wood, you may be able to remove it by scrubbing with an abrasive cleanser, such as Ajax or Comet. But if the stain has been there for a while—for example, a can of motor oil that has leaked on a tabletop in a garage—this will probably not work. Here’s how to remove the stain. First, wipe several times with a fast-evaporating solvent such as acetone to wipe off the surface oil. Then, mix a little of the acetone together with some fuller’s earth to make a paste. Fuller’s earth...

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Spray Pattern Heavier on One Side

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A spray pattern, with all the controls on the spray gun wide open, is supposed to be an even, elongated oval shape. If the pattern is heavier on one end than the other, the likely cause is that one or more of the holes in the air cap is plugged up. It’s also possible that the fluid nozzle has been damaged. To determine which, rotate the air cap one-half turn (180 degrees) and spray again. If the disrupted pattern switches sides, the problem is in the air cap. If the pattern stays the same, the problem is the fluid nozzle....

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Acetone Basics

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You may have noticed that acetone is becoming more widely available. This is primarily because it’s the only commonly available solvent (not counting water) that isn’t classified as a VOC or HAP. VOC is the acronym for volatile organic compound—that is, an environmental (smog) pollutant. HAP is the acronym for hazardous air pollutant—that is, something that is bad for us to breathe. Though acetone has a strong odor, making it seem to be toxic, it’s actually a fairly benign solvent in vapor form, limited at low exposure to causing only mild irritation to the central nervous system. Not being a...

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Polyurethane Won’t Dry

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If you experience oil-based polyurethane not drying well, it’s not likely that it’s bad polyurethane. It’s more likely that the wood you’re finishing contains a natural oil or you have applied an oil to the wood and the oil hasn’t dried. In both cases we’re talking only about the first coat of polyurethane. After the first coat has dried, there shouldn’t be any further drying problems. Most exotic woods (woods from jungle areas), with the exception of mahogany, contain a natural resin that is very oily. You can feel the oiliness. The mineral-spirits solvent in the polyurethane is also the...

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