How To Finish Rough-Cut Lumber

Rough-cut lumber is just what the name implies: it's fuzzy with exposed fibers with an inconsistent surface. Rough lumber may contain saw marks, insect holes and bark. It imparts a rustic ambiance that you just can't get using milled lumber. A proper finish keeps rough wood supple, prevents it from fading, cracking and enhances its natural beauty.

The use of rough lumber is on the increase in upscale, high-end homes and businesses. It's used for open beams, trim, panels or anywhere that contractors, designers or homeowners want to add a lodge-like feel to the room. It's ideal for a robust bed frame, structural supports, shelving, mantels or even entertainment centers.

Traditional film-forming top coats such as varnish or lacquer are not appropriate for rough lumber. They fail to penetrate, and with the fuzzy texture of rough lumber, top coats are — at best — difficult to apply. The thick viscosity of film-forming top coats rob the lumber of it's rugged ambiance by making it look more ordinary milled lumber

If you are still intent in adding a finish, with all the blends and variety available, the differences among products can be overwhelming. Oil-based products are the best overall to use with rough lumber. Oil-based products penetrate to protect; when applied in sufficient quantities, they provide a perpetual wet look that makes rough lumber easier to clean and dust. Oil-based products can be reinforced at regular intervals, and for the most part are non-toxic; they seal wood to protect it. You can also pick up stain and finishes combined in one product to add color to the rough lumber, if desired.

Boiled linseed oil and polymerized tung oil are two common products for finishing rough lumber. Boiled linseed oil is the least expensive, but it takes longer to dry than tung oil, and doesn't provide the water-resistance of tung oil. Tung oil highlights grain patterns better and is more aesthetically pleasing than linseed oil.

For the best results, an airless sprayer works better than using a cloth or a paintbrush. Work in a well-ventilated space or open garage.

Airless Sprayer

Rough lumber has splinters, fibers and rough grain that make oil difficult to apply with a brush or cloth. Spraying atomizes tung oil into fine particles that penetrate into cracks, crevices and under fibers better than brushing it on.

1. Choose the Right Tip

Install a .011 tip airless paint tip on the gun. Since tung oil is relatively thick., the right paint tip provides an appropriately thick coating on the rough lumber.

2. Test the Pattern

Hold the gun about 8 inches from the surface of a piece of scrap wood tilted at about a 45degree angle. Spray a short burst of tung oil. The pattern should be about 8 inches wide. It's OK if the tung oil runs slightly, but it shouldn't be dripping wet. Adjust the gun's settings as needed.

3. Coat the Wood

Pull the trigger and sweep the pattern along the wood from side to side at the right distance from the wood. Repeat immediately, overlapping the first pattern by about 1 inch. Continue working in the same manner until all visible sides are coated. If you're working with lumber that can be picked up, turn it over and spray the bottom.

4. Air Time

Wait one hour, and use a soft cloth, if necessary, to dab up pools of excessive tung oil. Because of the coarse texture of rough lumber, this step may be unnecessary depending on the condition of the wood. If it's excessively dry it will drink up the oil readily, and won't need to be wiped off.

5. Repeat and Dry

Repeat spraying one or two more coats as desired.

You don't need to do any sanding whatsoever. Sanding rough lumber before, during or after finishing detracts from its natural beauty, and is not necessary, unless you prefer to do so; in that case, it might be easier to buy smooth-milled wood instead.