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Q. Cleaning Old Beams

What’s the best way to clean embedded dirt and stains from an existing post-and-beam frame?

A. Dan Kolbert, of Kolbert Building in Portland, Maine, responds: We found the solution to this problem through trial-and-error when, as part of a major gut-rehab project, our company was asked to clean up an existing timber frame in place. The post-and-beam structure had been erected in the 1970s from pieces of other frames, and some of the original members dated back to the 19th century. The wood had a pretty thick layer of dirt and grime, and we were looking for a way to preserve its character while improving its appearance.

We tried a few simple solutions without success. Oxalic acid didn’t do much, nor did soap and water. Air hoses didn’t touch it, and wire brushes would have taken forever.

Finally, we were referred to Dyers Soda Blasting, a local business about an hour north of Portland. Dyers offers three different types of blast media for different situations: walnut shells, ground glass (which can strip paint off metal while not damaging the metal), and sodium bicarbonate (ordinary kitchen baking soda). We knew walnut shells wouldn’t work — we’d wasted a day with a rented sandblaster only to find that the ground walnut shells left the wood surface pitted and removed dramatically different amounts of summer and winter growth.

Jim Dyer, the company owner, came to our site with a blaster and tested the soda on a beam we had removed to build a dormer. The clients liked the look of the sample, and the price was around what we had scheduled for cleaning, so we made the deal. Jim and his crew got the entire house blasted in less than a day, and all that was left behind was a small pile of baking soda and sawdust.

The final results made our clients happy. The beams still look old, but the surfaces are clean and don’t make you nervous about leaning on them with clean clothes.