cleaning limestone

["John Vancamp" <jvcstnwrks@zzzzzzzzzzzzz>]

I'm writing in hopes of receiving feedback about methods that are safe
and effective for cleaning limestone masonry construction. My limestone
constructed home of 200+ years of age is in need of repointing and as
part of the process I want to clean the limestones with as little damage
as possible. The stones are stained and discolored with organic material
as well as portland cement. A previous home owner recklessly used
portland to fix a few of the masonry joints. I think some sort of media
blasting would probably work but I'm curious if anyone has some specific
ideas on this.

Let me take a stab at this.  First off, blasting limestone with any
blast medium will have a definit effect on the appearence of the stone.
Even pressure washing at high pressure can do conciderable damage.
Much of the organic staining can be dealt with by using bleach.  In my
shop I often use bleach full strength ( grocery store bottle) to remove
the black surface weathering that occures when the stone sets out in
the bone yard for a while.  I just use a pump up garden sprayer to
apply, let it sit ond do it's job, and then rince.  Particularily heavy
stains might take several applications.  The portland mess may need to
be removed mechanically.  Do not use any masonry cleaners that contain
acid.  Repointing is another mattere, and with a structure that old,
repointing probably should be done with a lime putty mortar rather than
a hard portland cement mix.  Tomas Lipps (who contributes here) has the
stone foundation ( www.stonefoundation.org ) web site where you can
probably get information about this.

John VanCamp / JVC Stoneworks

John Vancamp
jvcstnwrks@-------------
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