Soda blasting

Gerron Hite <gerron.hite [at] thc__state__tx__us> writes

>I am the Cemetery Preservation Coordinator for the Texas Historical
>Commission in Austin, Texas. My question involves the use of soda
>blasting to clean gravestones.
>
>I am aware of at least one contractor, with a construction
>background, in the state using this technique to clear stones.

I am surprised about the idea of using soda (Na2CO3), a water
soluble salt, as a abrasive for blasting. What is the advantage of
soda in this application? Salt efflorescence is the most common
cause of stone  deterioration. Usually you use something inert as a
blasting medium, like corundum powder. Or, if you prefer something
softer, marble powder (CaCO3).

Anyway I agree with Mr. John Horton: wet cleaning should be the
first choice on limestone and marble. Usually, the black crusts
consists of gypsum, witch can be washed away by water spraying.

Olaf Pung, stone conservator, Berlin


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                  Conservation DistList Instance 14:51
                  Distributed: Tuesday, April 3, 2001
                       Message Id: cdl-14-51-012
                                  ***