I am moving into a house (built 1911) that had a few things turn up on the inspection.

One corner of the basement has an indoor cistern, and there are some gaps and a hole in the cinder blocks just above ground level.

The below photo is from that corner, just above the cover to the cistern. You can see light coming through from outside (the top of the cistern is right at ground level).

The inspector mentioned that it would be easy to fix this via expanding mortar, but the information that I'm finding (i.e., Nonset 400) says that expanding mortar should not be used on vertical surfaces. I presume this is because the wet compound would sag or bulge while drying.

What is a suitable method/material for these type of repairs?

Gaps in basement wall

The cistern, for reference:

indoor cistern

2 Answers 2


Ultimately, I used two different types of cement for these two issues.

For the narrow gap, I used Quikrete Mortar Repair No. 8620-09, since it is advertised as a tuck-point compound. This is a light acrylic foam that hardens into a mortar-like substance. The applicator was able to inject the compound into the crack pretty easily.

Quickrete Mortar Repair No. 8620-09

For the larger hole in the concrete block, I use Quikrete Hydraulic Water-Stop Cement.

Quikrete Hydraulic Water-Stop Cement

I had never used either of these before, but the instructions were easy to follow, and I was pleased with the results. The Quickrete cement dries quickly (5 minutes) so I had to work fast when using it.

Sealed foundation

  • 1
    Excellent - thanks for coming back to answer your own question!!
    – FreeMan
    Commented Jun 30, 2020 at 14:18

If all you want to do is block the hole for insulation purposes then expanding foam is a good solution, it's cheap, easy to use and insulates well. It may be too thin a gap to get the nozzle in though. If you want something you can paint, or that matches the surface of the wall then you would want to put some mortar in there. You could do both - put a squirt of expanding foam in the center of the gap to insulate, then put regular mortar on the inside and outside for cosmetic purposes, with the added benefit of preventing water from getting in.

  • I seriously considered using expanding foam (and others had suggested it to me as well), but I ultimately decided against it because it is an exterior wall and I didn't want something that could absorb moisture and potentially be a source of mold.
    – Parker
    Commented Jun 30, 2020 at 13:46

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