Woodworker's Journal 2006-30-5, страница 63

Some Finishes Are Just Fickle

By Michael Dresdner

Michael Dresdner is

a nationally known finishing expert and the author of The New Wood Finishing Book by Taunton Press. When not writing about woodworking, he is an active

community theater

participant.

Contact us by writing to "Finishing Hotline," Woodworker's Journal, 4365 Willow Drive, Medina, MN 55340, by faxing us at (763) 478-8396 or by e-mailing us at: finishing

©woodworkersjoumal.com Please include your home address, phone number and e-mail address (if you have one) with your question.

ABOUT MICHAEL DRESDNER

Michael Responds: An "organic vapor cartridge," which is called just that by manufacturers and vendors, will handle the common solvents you are likely to use, but to work well, it must be paired with a pre-filter to stop airborne finish particles and dust. Most companies offer three types of pre-filters, designated "P" for oil-proof, "R" for oil-resistant and "N" for not for oil. If you do not spray oil-based coatings, you may be able to use the slightly cheaper "N" grade, but for wide-spectrum protection, your best bet is a "P"-type pre-filter atop an organic vapor cartridge.

I made a coffee table using ash for the top, poplar for the aprons and pine for the legs. I applied Olympic Red Mahogany stain, and it was perfect on the white pine legs and poplar apron, but it is not dark enough on the ash. I've applied three coats, waiting as long as possible before wiping off, and it doesn't look any darker. I can make

11|\ I'm making a flute Vfijf case for my daughter out of cocobolo and was wondering what kind of finish I should use. I was told that some finishes are not compatible with this wood.

— Christian Bradley Bellevue, Nebraska

Michael Responds: That's true. Cocobolo is a Dahlbergia, a member of the rosewood family and a group of woods that contain a natural antioxidant. As a result, they interfere with the drying of finishes that cure through oxygen polymerization, including most oil-based finishes. Coatings that cure through solvent evaporation, such as shellac, lacquer and water-based coatings, will all work. Of these, an exterior water-based polyurethane is your best bet.

Were it not for the wood restriction, my first choice for a flute case would have been an exterior oil-based polyurethane. It has the ability to withstand heat, cold, wood movement, water, abrasion and all manner of chemicals. Fortunately, there is a way around the antioxidant problem. Seal the case first with one coat of Zinsser SealCoaC, a dewaxed shellac- based sealer that is compatible under oils and will act as a barrier to the antioxidant. When the SealCoat is dry, apply several coats of exterior oil-based polyurethane.

j[ if What types of ^mM cartridges and filters should I be using in my respirator? I use the typical solvents and finishes most woodshops use.

—Jeff Dam on Wasilla, Alaska

Wood species can be a factor when deciding which finish is appropriate. Michael gives our reader the lowdown on finishing cocobolo.

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October 2006 Woodivorker's Journal