Tropical hardwoods, like Cocobolo, are prized for their beauty, durability and longevity. Using these woods can present its own set of challenges, though, namely in finishing them properly. Cocobolo is no exception. Even though your finish choices may be a bit limited when using this tropical hardwood, don't let that deter you from experiencing the joy of creating with such a beautiful wood.
Clean the Surface
Being native to the Pacific areas of Central America, Cocobolo is a very dense wood that resists rot. The reason it is so rot-resistant is a natural silica that is produced within the tree. While this is a great advantage in the longevity of the wood, it presents an apparent disadvantage to woodworkers looking to utilize this beautiful hardwood.
The natural silica prevents most finishes from adhering to Cocobolo, eventually peeling or never bonding in the first place. The key to finishing Cocobolo is surface preparation and using a film finish that doesn't react to the natural silica in the wood.
Since you can't stop the wood from producing this substance you need to clean off the residue with Naptha or Acetone and a clean cotton rag. You'll see discoloration on the rag as you clean the wood. It's a good idea to wipe it down a couple of times to make sure it gets clean. This makes the surface of the wood clear of the silica so that the finish can adhere properly and form a bond with the wood to prevent it from lifting off.
Choose the Right Finish
Oils like linseed and tung oil, and oil-based finishes like varnish, do not always bond with Cocobolo even when you clean the surface. To ensure a proper bond and lasting finish, it's always best to use a film finish. A film finish is a finish that sits on top of the wood and builds in layers as it's applied. The best and most versatile film finish is shellac.
Shellac for Success
Shellac comes premixed or in flakes that must be dissolved in denatured alcohol. Using premixed can save time, and if it's too thick, you can cut it with the denatured alcohol.
Shellac can be brushed, wiped or sprayed onto the wood. The easiest method is to pad the shellac using a wad of cotton cloth wrapped in another layer of cotton. Wet the inner pad with shellac and wrap it tightly in the second layer to form a pad. Use nice long strokes when padding shellac. Don't rub back and forth because the pad can pull of the layer you just wiped on. Just wipe it on in long strokes in one direction.
If you thinned the shellac enough, it can dry very quickly. After it's dry to the touch, you can apply another coat. Keep building like this, with a quick swipe of #0000 steel wool in between coats to allow for better adhesion.