We are restoring an 1800 post-and-beam barn. I am looking for a solution to clean up all the old posts and beams. The barn has been home to bats, squirrels, and chipmunks for the past 15 years. The beams are all hand hewn.
Those friendly little forest critters can leave behind a monumental mess when they leave. How extensively you clean up after them depends entirely on how you plan to use the space and how fastidious you are.
If the barn is to remain a barn in the next chapter of its life, where it's not important to remove every trace of its history as a rodent motel, cleaning and disinfecting the surface may be enough. I'd start by attacking crusty surface deposts with a wire brush and follow that with a stiff scrub brush.
Spraying the surface with a mild bleach solution kills bacteria, a prudent step.
This treatment won't remove surface stains. If that's important, I'd try a mild soapy solution with a scrub brush and rinse the surface with clear water. Given wood's porosity, some stains will almost certainly remain. But this low-impact treatment is unlikely to do any permanent damage to the surface of the wood. It will still look like a hand-hewn barn that's been around for a while.
More aggressive approach, greater risks
There are two other possible techniques, both of which ought to be approached with caution. One is a power washer, which forces water or a cleaning solution through a nozzle at very high pressure. Painters often use them to remove scale, loose paint, dirt, and other debris on house exteriors before repainting.
They're very effective, in the wrong hands too effective. These machines are entirely capable of removing wood fiber along with everything else. If you've never used one before, you might want to start by practicing on some scrap to get an idea of just how powerful the power washer really is. Or hire someone who's had a lot of practice.
Sand-blasting with a mild abrasive like ground walnut shells is the other possibility. Walnut shells are softer than abrasives such as steel shot or aluminum oxide, so the risk of damaging a relatively delicate material like wood is much lower. This would probably require you to a hire an outside contractor, and would certainly cost more than a simple brush and scrub.
But if it's important to return the surface to near pristine condition, it's something to consider. I'd be very careful who I hired, and I'd want to know how much experience the company has had working on old buildings.
Beware the little mouse
No matter what you do, take some basic precautions when working around animal droppings. For example, cleaning up droppings from the deer mouse can cause Hantavirus Pulmonary Syndrome, a rare but potentially deadly condition that shows up as fever and respiratory distress a few weeks after exposure.
Wear a HEPA respirator and rubber gloves for these jobs, and wash down affected areas with a bleach solution when you're finished.
When in doubt, do less
We save old barns and re-use old barn board because the wood has a texture and color that new materials lack. Clean too vigorously and you destroy the very thing you're working so hard to maintain. If you wanted a new building, you would probably hire someone to build it.
We might take some guidance in the advice that all physicians get during their training--first, do no harm.
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