Q: In the process of remodeling my house, built in 1904, I uncovered Douglas fir flooring that appears to be in good shape after being hidden for nearly 40 years under red shag carpeting. But I have received conflicting advice about how to refinish the floors. One contractor told me to rent a commercial floor sander, then finish with a rotary sander. Another contractor said the big machine has a tendency to damage a floor, so I should work only with the rotary sander. What do you think?

— Marty, Colfax, CA

A: Tom Silva replies: Why would you want to get rid of red shag? It's a great conversation starter. Seriously, I bet the Doug fir will be beautiful. Flooring that old is bound to have tighter grain than anything that's affordable these days. But if you have a whole room to refinish, the fastest way to tackle this is with a commercial floor sander, often called a drum sander. These high-powered sanders, widely available at rental centers, are also quick to destroy a wood floor, particularly one as soft as fir. So be very careful — or turn the job over to a professional.

Or, Instead of a drum sander, rent a disk sander, a relatively new type of floor sander with four separate sanding heads. It's not as aggressive as a drum sander and so takes longer to get the job done, but that makes it more forgiving of inexperienced operators, particularly when a floor is uneven. The homeowner of the Salem, Mass., TOH TV project used this kind of machine on his old pine plank floors, and they came out looking great.

I suspect the rotary sander you refer to is actually a floor buffing machine, a single head fitted with an abrasive screen. A "screening,"as it's called, is much too slow to remove a finish. It's for smoothing bare wood, or roughing up the finish on slightly worn floors before applying a new coat of finish.

For an overview of what's involved in refinishing a floor, see Refinishing School, or check the Web site of the Wood Flooring Manufacturers Association (www.nofma.org).

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