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TIP: Finishing Oily Woods

acetone finish oil the finishing store wood woodfinishing woodwork woodworking

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. Don’t wait a long time before finishing or the oil that is deeper in the wood will rise back to the surface. It’s best to remove the oil with naphtha because it evaporates rapidly. You can also use acetone, but if there are several woods involved, as in the accompanying picture, acetone is much more likely to lift some of the color from the darker wood and transfer it to the lighter wood.

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