How to Repair Cinder Block Foundations

Repairing a cinder block foundation is difficult, dirty and exhausting work. Although the steps are simple, the work is not. If this does not sound like your type of thing, call a contractor and save yourself the trouble. But if you are up to the challenge, follow the steps to repair the two most common problems -- a basement leak or a large crack.

Things You'll Need

  • Plaster premix
  • Trowel
  • Foundation tar
  • Drain tube
  • Premixed cement

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Basement Water

Dig down to the building’s foundation. Dig all the way to the bottom, where the foundation meets the earth.

Mix cement premix until it is sticky and runny.

Apply the mix to the outside portion of the cinder block wall, using broad strokes and a wide flat trowel. Apply it 1 inch thick, all the way from the base of the foundation to the place where the foundation meets the ground’s surface.

Allow the plaster mix to set for two to three days.

Coat the dried plaster with foundation tar. Let it sit for another day or two.

Install a drain tube along the bottom of the foundation to catch water before it enters the basement.

Foundation Cracks

Create a crumbly, dry mixture of premixed cement.

Pack the mixture into the crack in the foundation. Make sure you pack it in as tight as you can get it.

Watch the crack for the next few months to see if it reappears. If it does, call a contractor immediately.

Tips & Warnings

  • If your foundation has a small crack in it, don't be alarmed. Just dab a little cement premix over it and forget about it.
  • If the crack in the foundation is more than an inch wide, call a contractor immediately. This could indicate that a corner of the foundation is settling.


  • "Successful Home Repair: When Not to Call the Contractor"; Gary Paulson; 1978
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