Removing stain from columns

Our church has four large concrete columns, some parts of which have turned black. We are told that sandblasting would ruin the surface. How can the black stain be removed without damage to the pillars? Harold Johnk Greenfield, Iowa

Prosoco Inc., of Kansas City, Kan. (913) 281-2700, makes a product called Sure Klean Limestone Prewash and Sure Klean Limestone Afterwash. Other products may be available as well.

The manufacturer declares that Prosoco products will work in sequence on concrete as well as limestone. One Prosoco dealer near you is Stetson Building Products in Des Moines. The phone number is (515) 243-6286.