Step-by-step approach to waterproofing the steps: Part 3 of 3

THIS IS THE CONCLUSION of 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.

Front steps of our sanctuary, Feb. 2023, prior to installation of fence/gates
(As usual, click/tap on an image to enlarge it.)

In May, the board agreed to authorize this project “as funds become available.” Since then, I have been finalizing plans. Below the jump, I discuss the last of the three steps involved.…

Step 3:  Sealing the stone and grout surfaces

In August, Guillermo Groisman (retired architect and general contractor) told me about a company that sells waterproofing coatings, and that has very knowledgeable sales reps. It’s now called Beacon Roofing. At my request, one of their reps made a site visit to our front steps. He promptly recommended a specialized penetrating sealant called SINAK HLQ-125 and sent me product literature. (None of the various contractors whom I'd consulted had ever mentioned it.)

Then I spoke by phone with Jeff Mosely, Director of Technical Services for SINAK. Happily, he seemed well versed in the chemistry of masonry/concrete-related products, and experienced in working on historic buildings in the L.A. area. He said that he has seen this product work well on sandstone, and he sounded very confident that it would suit our needs. He made the following points:

• SINAK HLQ-125 would be applied across the whole surface of the steps and patio. It reacts chemically with the silica in the sandstone, not only waterproofing it but also strengthening it—making it more stable and reducing the flaking of its layers in the future. Therefore the waterproofing treatment would last longer; it would be relatively permanent. (It also makes the sandstone more stain-resistant.)
• This product is best applied during the coolest part of the day, out of direct sunlight, because that is when the dynamic cracks in the surface are largest, so the sealant can get down into those cracks.
• The sandstone would be very thirsty, soaking up this product readily. Jeff expects that six coats would be needed. 
• Application as follows: in a crosshatch pattern, starting with a light mist coat to break surface tension; then successive coats at 50–75 sq ft/gal coverage, waiting until the surface is dry to the touch in between; keep going until the liquid no longer sinks in on its own, i.e., the surface remains damp in places; then broom that excess liquid to force it into the adjacent drier spots.

After a modest restoration in July 2021