- Q.I have some 8x16-inch
Douglas fir beams that have black stains from the steel
saddles. How can I remove the stains? Can I use a
solution of oxalic acid crystals?
A.Henri de Marne
responds: First, you should find out what
caused the steel saddles to stain the beams. Such
stains are usually caused by water contact.
Since the steel saddles would not have stained
the beams if they had been painted with a
rust-inhibiting paint before installation, I assume
the saddles were installed raw. You can use oxalic
acid to remove the stains, but the work will be
tricky because the acid solution should not come in
contact with metal of any kind. You will have to
mask the metal carefully before applying the acid
solution to the beams.
You can buy oxalic acid crystals from a paint,
hardware, or janitorial supply store. You
won’t need much. Dissolve the acid
crystals in warm water in a glass or plastic
container. The acid crystals should be mixed to
saturation — that is, until some of the
crystals will no longer dissolve.
Carefully apply the solution to the stained area
with a small brush, without letting any drip.
Removing the stains may require more than one
application. Use extreme caution; oxalic acid is a
very potent chemical. Wear rubber gloves, and skin
and eye protection.
Once the stains are gone, wipe the treated areas
with a sponge or clean cloth dampened with white
vinegar in order to remove any crystal residue.