Finishing Oily Exotic Woods
The thought of applying finish to a project can be enough to kick up your pulse rate and blood pressure, especially when the project contains an "exotic" wood full of natural oils [Photo, below]. That's because the oils and resins in woods such as cocobolo, rosewood, padauk, purpleheart, teak, and even eastern red cedar can markedly slow or practically stop a finish from bonding or curing. These wood species require different preparation before finishing. Follow these helpful tips to make the process smooth as silk.
Prep, seal, then topcoat
Typically, I sand to 150 grit for projects receiving stain. But because we prize exotic woods for their inherent color, skip the stain and apply a clear topcoat. For oily exotics, sand instead to 220 grit for a smooth surface that allows any finish to bond well. Remove all sanding dust between grits.
Eliminate any oils from the wood by wiping down the freshly sanded surface with a fast-evaporating solvent [Photo, above]. Then, apply one or two coats of dewaxed shellac, such as SealCoat, sealing the wood and preventing additional oils from migrating to the surface [Photo, below]. A very light sanding with 400-grit sandpaper between coats smooths the surface and removes dust nibs. The prepped surface is now ready for your choice of topcoat.
Choose the best topcoat by considering the intended use of the project: Furniture subjected to heavy use benefits from varnish or a durable oil- or water-based polyurethane finish. A sprayed catalyzed lacquer is also a good choice for experienced finishers.
For decorative pieces and projects that see less wear, try a simple buffing [Photo, below], regular nitrocellulose lacquer, or additional coats of shellac. A quality paste wax also suits those projects.
If you apply finish to an exotic-wood project and discover a sticky or tacky finish days later, don't lose faith: Try these options.
First, be patient. The oils and resins can delay the curing process, so with a little more time, the finish may harden. But be aware that the tacky surface will trap dust during the wait.
Second, a vigorous wiping of the surface with a fast-drying solvent may remove the uncured finish. If that works, follow with a light sanding and a couple of coats of dewaxed shellac to seal the surface and prevent any additional bleed-through. After the shellac cures, reapply the topcoat.
As a last resort, consider it a lesson learned, and scrape, sand, or strip the old finish completely and start over. An out-of-date finish may not cure, so test-apply the finish on scrap to check for freshness before recoating.
The beauty and character of exotic woods should increase interest, not angst, in your projects. Now that you know how to handle those oils, you'll find finishing Nirvana.