Penetrating resin finishes, unlike varnish, are not surface finishes; they soak into the wood to harden the fibers themselves. Wood treated with penetrating resin has a very natural look and feel, as if it were unfinished, and the grain is strongly highlighted. Penetrating resin is very durable and withstands heavy wear; it is both easy to apply and easy to repair. It dries clear, but it darkens the wood slightly. It is also available in several stain colors.
Because penetrating resin must soak into the wood, it is best used on open-grained woods. Very close-grained woods may not absorb it deeply. On stripped wood, all old filler must be removed. If filler is left in the wood, the finish will not be absorbed.
Penetrating resin is recommended for use on oily hardwoods, such as rosewood and teak, and is especially effective on oak and walnut. It is often preferable to varnish for use on large pieces of furniture and complex carvings. It dries relatively slowly, but because it is not a surface finish, dust is not a problem. A penetrating resin finish is very hard to remove for future refinishers, so it's important to choose the right one for the job.
Types of Penetrating Resin
Penetrating resin finishes are formulated with two different types of resins: phenolic and alkyd. There is little difference in performance between these types, but phenolic-base compounds may penetrate the wood more deeply than alkyd types.
Penetrating resin can be used over any stain except varnish- or vinyl-base types. No filling or sealing is required. Before applying penetrating resin on bleached or stained surfaces, test it on a hidden part of the piece.
Penetrating Resin Application Techniques
Wood to be finished with penetrating resin must be properly prepared and sanded. Because the finish does not coat the surface of the wood, any rough spots or other defects will be accentuated when the resin is applied. Immediately before applying the resin, clean the piece of furniture thoroughly with a tack cloth.
Whenever possible, penetrating resin should be applied to horizontal surfaces. If the piece of furniture has removable parts, remove them and finish them horizontally. Apply penetrating resin with a clean brush or cloth, with No. 0000 steel wool, or pour it directly onto the wood. Work on small areas at a time. On rungs or spindles, apply the resin with a clean cloth one rung at a time.
Spread the resin liberally and evenly over the wood. The appearance of the surface isn't critical, but the amount of resin used on each surface should be consistent. As you work, watch the wood surface. Some open-grained woods soak up the finish very quickly, others -- especially close-grained hardwoods -- absorb it slowly and may not absorb much. Apply resin until the wood stops absorbing it.
Let the resin set for about 30 to 45 minutes. During this time, keep the surface wet, adding more resin to any dry spots that appear. All surfaces should be shiny. After 30 to 45 minutes, when the wood will not absorb any more resin and the surface is still wet, firmly wipe off the excess finish with clean, absorbent cloths. The surface of the wood should be completely dry, with no wet, shiny spots.
Drying and Recoating
Let the newly applied resin dry for 24 hours. If glossy patches appear on the wood during the drying period, remove them immediately. Add resin to these areas to soften the dried finish, and wipe off the liquid resin so that the wood is dry.
After 24 hours, smooth the wood gently with No. 000 or 0000 steel wool; then clean it thoroughly with a tack cloth. Apply a second coat of penetrating resin, letting it penetrate and wiping off the excess as above. If necessary on very open-grained woods, apply a third coat of resin; wait 24 hours and smooth the surface with steel wool before application, as above. No wax or other surface coat is needed.
If you need a finish that is easy to apply and dries quickly, then check out the next section for tips on when and how to use a shellac finish.