I have a building faced with travertine building stone. Many of the large natural voids in the stone were filled with a patching material. These patches are coming loose in many locations and falling off the building. Is it necessary to replace these patches for the durability of the stone? If so, what should I replace them with?
The patches may not all need to be replaced. If a void is smaller than a golf ball in diameter, if its bottom surface slopes away from the stone, and if no open veins extend into the bottom, sides, or back of the void, replacing the patch may be unnecessary. If voids are to be filled, a cementitious patch should be used. Patches made from an organic material such as polyester or epoxy will shrink over time due to exposure to ultraviolet light. Epoxy patches also may expand thermally more than the stone and cause cracking. An acrylic-modified Type N mortar normally performs well. Stainless steel (300 series) "J" anchors should be used to attach the patch mechanically to the stone. Generally, use one anchor per patch or per square foot for large patches.