Q: My son accidentally spilled melted butter on an unfinished countertop of bare fir plywood. What could be used to clean it so that water-based paint would stick to it?
Greg Williams: Apply a poultice of Fuller’s earth and water (a paste) liberally to the surface, and then heat the surface to 120 F or so. Repeat several times to draw out as much of the oil as possible. A wash coat of dewaxed shellac, such as Zinsser SealCoat™, before the water-based paint would help the adhesion.
Michael Dresdner: Another method is to scrub the area with liberal amounts of mineral spirits on a nylon abrasive pad, and then sop up the slurry with paper shop towels. Repeat, then after the wood is dry, seal it with a good primer, such as Zinsser BIN®, prior to painting, assuming that by paint you mean a solid opaque color and not a clear finish.