We have a cinder block foundation in our 1920s home. When we moved in, the basement was somewhat damp with elevated humidity readings. We can see some efflorescence on the foundation walls, but no visible water. The surface of the wall is crumbling in a few places. There is no evidence of hydrostatic pressure from below the slab. Currently, we manage the humidity quite well with two small dehumidifiers (~45%).

Is there any structural benefit to applying any type of coating to the walls (e.g. hydraulic cement or epoxy), or would that only be for the purpose of water-proofing? Would it extend the lifespan of the foundation?

1 Answer 1


Surprisingly, introducing water to the CMU will actually increase it's strength because you're providing more fuel for the chemical reaction that turns it from a liquid to a solid. The only time water will cause a structural issue with the CMU is if it susceptible to frost. If you feel the wall is wet on the outside of the building on a regular basis and you live in a region where temperatures drop below freezing then it can cause freeze thaw damage and destroy the blocks over time.

Typically, waterproofing is applied to blocks strictly for architectural purposes. They don't want to allow water in to prevent efflorescence, they want to keep humidity in the building down, or they want to keep actual water out of the building.

  • Very helpful, thank you. Would interior waterproofing do anything to prevent freeze-thaw damage, or would only exterior insulation/drainage help?
    – ErnChe
    May 5, 2020 at 16:02
  • Interior waterproofing wouldn't help but you might want to think about creating a combination of the two if the wall is taking on freezing temperatures. The typical below grade assembly from interior to exterior is as follows... 1. CMU 2. Waterproofing membrane 3. Air gap ( composed of gravel for below grade purposes) 4. Native soils
    – represton
    May 5, 2020 at 16:09

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