Cleaning shingles on cottage which linseed oil turned black

Q. When we built our cottage on the New Brunswick shore, we had the outside walls covered with cedar shingles, which I hoped would turn gray as have other shingles in the area. The builder advised us to ''protect'' the shingles with linseed oil applied annually for the first three years. Now I find this was a mistake. The shingles, instead of turning gray, turned black. Is there any way to strip off the black color and get the shingles back to an unfinished state so they can weather naturally?

Christine J. Wilkins

A. Highland Beach, Fla. ''Several procedures may be used to remove the discoloration and return the shingles to their natural color,'' writes Marshall Ritchie of the Red Cedar Shingle & Handsplit Shake Bureau, Bellevue, Wash.

Mr. Ritchie says that wire-brushing by hand might remove the black, but it's tedious work. Electric wire-brushing would be easier. Two other methods are to cleanse the wood with a water blaster; or, less desirable, a sand blaster. The two latter methods would have to be done with sensitivity so as to avoid damage to the wood.

I'd first experiment with hand or electric wire-brushing in a small, inconspicuous area of the house. The brushing may gum up some, depending on the depth of penetration of the linseed oil. If gumming does occur, experiment with paint thinner to see if it alleviates the oil residue without further staining the shingles.

Again, experiment in a small, inconspicuous area where the shingles have been cleansed by applying semi-opaque gray stain.

For years, the shingle bureau has frowned upon any overtreatment of wood shakes and shingles other than at the factory.

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