The common drink coaster might not have the cache of a tech-muscled home security system, but just watch it stop a cold-beer stain from rendering a $2,500 redwood patio table an embarrassment.

As simple as it sounds, it is indicative of how fickle wood finishes can be. Just ask any commercial or residential painter.

“Wood is a natural material, and wood will do what wood wants to do,” says Ken Byrd, owner of Redlands, CA-based America Painting Company. “And what we’re seeing today isn’t always the best wood, even if you’re using high-end materials. It can cause you more problems in treating and finishing it.”

GRAY, WEATHERED WOOD

Byrd understands the challenges of one of Mother Nature’s favorite sons, wood, and the havoc the elements can play with a wood finish.

“I had a customer who purchased installed cabinetry that had been exposed to water at some point, causing the wood to turn gray,” Byrd says. “The customer had bought the cabinets installed and didn’t realize what he was buying. Stain will not cover gray wood; you have to sand it down to fresh wood, or use a chemical wash; you can even use bleach and water to neutralize the gray.”

LAP MARKS

One of the most persistent problems pros encounter on a job is lap marks.

“Lap marks are one of the more common staining problems,” says Bill Gradisher, a technical expert in the R&D department at PPG Architectural Coatings. “These occur when wet and dry layers overlap during staining. The most common cause is finishing the wood when it is too hot or windy.”

Gradisher says the ideal time to apply stain is when the temperature is between 50º and 90º F, but never apply it in direct sunlight. He says another cause of lap marks can be inadequate stirring of the stain prior to the application.

“To prevent lap marks, mix all stains thoroughly beforehand, and periodically during the application,” he says. “Staining too large an area at one time can also cause lap marks. Always stain the entire length of a deck board or horizontal siding board to a logical break, such as a door or window, and do not stop in the middle of a board. If a spray applicator is used, back-brush or back-roll to improve penetration and uniformity of appearance.”

BLOTCHY, UNEVEN FINISH

No painter wants to see a blotchy or uneven finish, but this can be another problem of staining, says Gradisher. “The most common cause of this is inadequate cleaning of the wood prior to the application of stain,” he says. “The wood should be cleaned with a chemical cleaner.”

Gradisher says if the customer wants to use pressure washing, it should not be the primary means of cleaning, but rather a means for rinsing the cleaner from the wood.

He recommends using a cleaner and brightener product, in conjunction with pressure washing.

“This will eliminate the need for higher pressure and reduce the likelihood of damage to the wood during the cleaning process,” he says.

HOLD THE OIL, PLEASE

Another common problem that Byrd frequently sees on the job is treating wood without a true clear finish.

“When this is the case, applying an oil is really not going to help you,” Byrd says. “Everyone wants to apply Murphy’s Oil Soap or one of these orange oils. But what you’re really doing, especially treating wood finished in a water-based or oil-based polyurethane, is breaking down the finish.

“Also, if you’re painting something that might have aluminum oxide on it; it doesn’t need to be treated with an orange-based oil. All you’re doing is making the wood sticky. You’re not helping it, you’re really degrading it.”

Byrd says orange-based products do have their place in treating wood, such as with older wood finishes that do not have a true clear finish.

“However, in today’s world, your polyurethanes, lacquers, and some types of marine varnish are just not going to accept oil on top of them to condition it.”

For those types of wood, Byrd suggests just using a microfiber cloth that is dampened slightly with water.

WATER SPOTS

Unless it’s still in tree form and rooted in the ground, wood doesn’t like water. Fact is, when wood gets wet, the grain rises and expands where the water has touched. This causes the wood to absorb the stain more readily, and discolor.

What to do about it? Byrd says one easy solution is to spot-sand the area, and then re-sand the entire surface, and reseal with a clear finish.

STAINS, PAINTS AND GRAINS

Just because they have a paintbrush in common, stains and paints are not created equal, Gradisher says.

“A stain is not paint and should not be applied in the same manner,” he says. “Most paints are generally applied in multiple coats, allowing the coats to dry between applications. Stains, on the other hand, are usually applied either in one coat or with a wet-on-wet application, meaning the first coat is not allowed to dry before the second coat is applied.”

Are some types of wood and wood grains more problematic than others? Absolutely says Gradisher.

“Yes, the exotic wood types—such as ipe, mahogany, ironwood and teak—have a dense cell structure that reduces the ability of a coating to penetrate into the wood surface,” Gradisher says. “Generally speaking, this type of wood needs to be recoated more frequently than the softer woods such as pine, cedar or redwoods.”

COMMON MISTAKES

Even a professional painter can make a mistake, especially when it comes to the wildly inconsistent nature of wood surfaces. One such error is not preparing the wood sufficiently before applying a stain, says Gradisher.

“Another mistake is to over-apply a penetrating stain, as more is not necessarily better,” he says. “In addition, not mixing together all stains that are to be used on a project can lead to an uneven coverage and appearance to the stain. And the finish must be maintained. Cleaning it with an acid-based cleaner at least once a year will keep the wood looking good and will allow the stain to last longer, cutting down on the need to recoat.”

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COMMON WOOD-FINISHING TERMS

Ambering: The tendency of a clear protective finish to take on a warm, yellow appearance as it ages

Bleeding/Bleedback: A staining phenomenon occurring when the stain seeps back to the surface of the wood

End Grain: The wood surface exposed when a board is cut across the grain, opening the elongated pores so that they absorb more liquid than the other parts of the board

Graining: A technique that uses stain to duplicate the grain pattern of a type of wood on a non-wood surface

Grain Raising: A condition that occurs on the surface of wood when its fibers absorb water, causing them to stand, and giving the wood a rough surface

Lacquer: A clear or pigmented protective coating, formulated with cellulosic or synthetic resins to dry by evaporation, forming a solid film

Leveling: The ‘flowing out’ of a freshly applied finish, during which brush marks disappear

Polyurethane Finish: An exceptionally hard and wear-resistance varnish noted for its overall balance of high-performance properties, including durability, abrasion resistance, and household-chemical resistance

Pores: Cell-like cavities that characterize the grain of the wood

Shellac: A varnish made by dissolving lac (a natural resin) in denatured alcohol

Solvent: Any liquid that can be used to dissolve other substances. The most common solvents in wood finishing are water, mineral spirits, denatured alcohol, acetone, turpentine, and toluene

Spar Urethane: A durable varnish formulated for exterior use; it remains slightly softer and more flexible than interior varnish, allowing it to expand and contract with changing weather conditions

Stain: Any of several products containing dyes and/ or pigments to add color to wood

Varnish: A preparation for coating wood surfaces consisting of resins dissolved in oil, denatured alcohol, or water

Terms reprinted with permission from Sherwin-Williams.