Q&As: Oil Finishes, Adhesive for Cork Underlayment, & Doug Fir in Bathrooms

By HF Editors
August/September 2011
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Figuring Out Oil Finishes

I am hearing a lot lately about “oil” finishes. What exactly are they?

Jeff Fairbanks, vice president at Denver, Colo.-based Palo Duro Hardwoods, answers:

In the wood flooring industry, when people mention “oil” finish, they often are talking about oil-modified polyurethane. But, there is a whole category of true “natural oil” finishes on the market, and they are experiencing a resurgence in popularity. There are many different types of oil finishes, and it can get confusing. I would say natural oil finishes fall into four categories:

1) Natural-based oil: The main ingredient in these finishes is the binder, which is a natural-based oil (e.g., sunflower oil, safflower oil, soja oil). These oils have a small amount of non-natural dryers so they will dry. Tung oils are included in this group.

2) Hybrid oil: There is a wide range of oil finishes typically based on vegetable oil. These finishes are often combined with alkyd resins for better drying and durability.

3) Hard wax oils: These finishes have natural vegetable-based oil combined with wax; the wax is normally “natural-based wax,” e.g., carnauba wax.

4) UV hard wax oil: This type is used primarily in prefinished lines. It is another variation of the hard wax oil; it has additives that react with UV light to cure faster.

The big difference in natural oil and oil-modified polyurethane, other than appearance, is the need for some type of routine maintenance. Most of the natural oil finishes will need to be “refreshed,” which is basically just another application of diluted product. The timeframe will vary (usually 6 to 12 months), just like all other types of finish, depending on the wear and tear. The best example I have seen was at the Mercedes Benz Museum in Germany. They use natural-based oil because they don’t need to recoat the entire floor—just the areas that need attention.

Putting Cork Under It

I need to install cork under an engineered floor; does it matter which adhesive I use under the cork?

Rusty Swindoll, technical services manager at the National Wood Flooring Association, answers:

I had a call on the NWFA tech line recently that should answer this question. The contractor had a job with about 800 square feet of ½-inch, 5-inch-wide engineered red oak to install over a ¼-inch cork underlayment on a slab. Before starting his job he had enough urethane adhesive for the engineered maple floor but not enough for the cork. He did have some leftover carpet adhesive in his truck, and he figured that should work fine, so he proceeded with the installation.

A few weeks later he got a call from an inspector to meet him at the job site. To his surprise, the flooring had cupped, and there were lots of hollow spots and deflection. When the inspector removed some of the flooring, he could see that the cork was turning loose from the slab. Apparently, the water in the carpet adhesive was trapped under the cork, and the vapors caused the wood floor to cup. Also, the inspection showed the trowel used was not correct.

What does this floor failure teach us? The contractor in this case didn’t follow the manufacturer’s recommendations for installing cork to concrete, either for the correct adhesive or the correct trowel, and this job will cost him. Always use what the manufacturer recommends, and be prepared with the right tools and materials before you arrive at the job site. The moment when you’re about to start installing a floor isn’t a good time to realize you’re missing something.

Wood in the Bathroom

I was told that Douglas fir is a good choice when customers want wood flooring in a bathroom. Is that true?

Nicole Morales, blogger for AltruFir, a subsidiary of AltruWood, answers:

Yes, it is, but there are precautions that you’ll need to heed before and after installation:

• Select a clear vertical grain (CVG) narrow-width Douglas fir product instead of flat or mixed-grain Douglas fir. The tighter the grain, the better the durability and resistance to moisture. CVG Douglas fir doesn’t absorb water as quickly as most other wood species because of the tight grain.

• Look around for moisture problems and make sure the customer has any leaky hardware replaced before installation.

• Make sure your product is kiln-dried. Once on the job site, acclimate it in the bathroom while the bathroom is in normal use (with the customer being careful not to get the boards wet). Acclimate it until the average moisture content reading between the flooring and the subfloor are within 2% of each other.

• For Douglas fir in bathrooms, glue-down installation is preferred over nail-down.

• Make sure you inform customers that they need to remove damp bathmats and wet towels from the floor immediately after use, never leave water standing on the floor, and ventilate the bathroom well. Also, emphasize other standard maintenance practices for wood floors, such as not wet-mopping the floor.

Wood floor adhesives    Wood floor finish    Trowels    Wood floor underlayment            Finishing wood flooring    Moisture testing wood floors                Oil finish    Doug fir