Throughout the past three decades of this ongoing timber frame revival, timber framers have tried just about every finish available. Some have worked well and some have failed miserably. The challenges are:
- finding a finish solution that is easy to apply, readily available and reasonably priced
- user, environment, and occupant safety
- durability and ease of repair
- choosing the desired surface appearance that is long-lasting.
That’s a long list and most finishes do some of these things and a few do most of them.
Natural Oil Finish
These finishes are typically composed of Tung oil, linseed oil and a natural solvent such as citrus extracts. A natural oil finish is simple to apply with a foam pad, roller or brush and is allowed to remain on the timber surface for up to one day, soaking into the grain. The resulting finish has a rich patina; and scuffmarks are easily repaired by using an abrasive pad saturated with finish. While the finish is wet your home will smell like an orange juice factory, but the citrus odor dissipates in two or three days. These products are a good choice, yielding an adequate finish that is easily renewed and with no toxic substances introduced to you or your home.
In addition to standard natural oil finishes, some manufacturers offer oil finishes with wax that can be buffed to a low luster.
Petroleum-Based Oil Finishes
Cheaper to purchase than natural oil finishes, petroleum-based Tung oil and linseed oil finishes have seen wide use. These finishes are a bit less forgiving in application as the excess should be wiped from the timber surface before becoming gummy. These products are right-off-the-shelf available and yield an attractive patina. Marred surfaces are easily patched. The big drawback has to do with the environment. The compounds are injurious to skin and lungs and saturated rags can combust. Most importantly, out-gassing of harmful compounds can occur over a long period of time.
Varnishes and Urethanes
Applying finish to timbers in a timber frame differs from applying finish to a piece of fine furniture. The wood in the furniture is dry and pretty stable while the timbers are surely less stable and must be allowed to breathe while they dry (usually 4-6 years depending on the species). Urethanes and the like seal wood surfaces, fostering mildew growth beneath the finish on green timbers and ultimately failing.