THIS IS THE SECOND in a series on how to address the following urgent problem:
During heavy rains, our historic sanctuary’s front steps leak water, which soaks the concrete substrate below the steps, which in turn drips water onto the ceiling of the rooms beneath it in the basement.
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Given the sandstone’s age, modest state of deterioration, and inherent instability, as well as the absence of waterproofing during initial construction, the fix is not simple or straightforward. Below the jump, I discuss the second of the three steps involved.…
Step 2: Filling in the cracks and gaps
First, power wash the surface gently, sweeping away the puddles afterward, and allow it to dry. (Perhaps our member who owns Star Kleen Service would donate this washing once again.)
For filling in the larger gaps (after digging out any loose pieces), Neil from Bonstone Materials—a restoration-oriented manufacturer of patching compounds—says that our need for color matching will determine which of their products is best suited. Their Last Patch Limestone compound can be custom tinted on site.
Alternatively, their Historic Restoration Mortar (HRM) is easier to work with, but it is available only in a palette of 16 colors. I.e., if one of those colors happens to match our grout well, then HRM would be the better choice. For HRM, Neil suggests a 5:2 mix ratio, using a spatula to work it in and smooth it out.
For filling in the sandstone surface cracks (less than 1/4" wide), Bonstone Materials recommends first cleaning with a cotton swab and denatured alcohol, then injecting Last Patch Gel. However, that product seems to have a glossy finish, so perhaps a better match would be a 180-ml cartridge of clear gel epoxy, which can be injected into cracks with a Manual Single Cartridge Gun, per directions.
Finally, for hairline cracks between stone and grout, Neil recommends Clear Penetrating Epoxy, which has a 40-minute pot time for each batch.
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