Waterproof foundation cracks by filling them in

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Need to do some foundation crack repairs and don’t know where to start? See how simple it is to repair and waterproof cracks to prevent future problems.

Have you started noticing cracks in your home’s foundation? 

No home is immune from it. Every house settles over time, with the weight of its belongings and the condition of its environment. 

Seasonal changes have a big impact. In winter, the cement freezes and contracts and in summer, thaws and expands, causing cracks. Also, too much water in the soil can put pressure on the foundation, forcing cracks in vulnerable spots. 

Our house is no exception and the basement has a few cracks along the cinder block foundation. 

Here is one example of the cracks in our basement:

crack in cinder block foundation

We knew we needed to repair these cracks but we also wanted to waterproof them. 

A big problem with cracks in foundations is that water can now penetrate into the house and cause damage to your walls and floors. 

We were in the middle of finishing our basement so it was a perfect opportunity to address any possible water problems. And the first (and most affordable) step is repairing any cracks and holes in the foundation.

Let me show you how easy it is to fill in a crack in the foundation. 

PLEASE NOTE: Some cracks in your foundation could be a serious foundation problem that needs to be fixed by a professional. If you’re not sure, have someone inspect the foundation.

Here’s what you need to patch and seal those cracks:

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  • hydraulic cement
  • H2O (water)
  • bucket
  • measuring cup (1/4″-1/2″ cup)
  • water spray bottle


SIDE NOTE: The cool thing about this cement is that it can be used even in emergencies, like when water is leaking into a basement.


The first thing I did was use the wire brush to scrub the area that needed fixing. This will remove dirt and particles from the foundation.


Then, I took the putty knife and ran it along the crack, following it as it continued to the stones below. This will widen and remove more loose foundation so you can do a thorough repair. 

The picture above is the foundation crack before and here it is after I widened it:

waterproof cracked cinder block foundation
fixing cracked cinder block foundation

TIP: A deeper/wider crack will help the cement get in easily.


Next, I took my shop-vac and vacuumed around the lines of the crack. 


Once I finished, I mixed my cement. I followed the instructions on the container. 

SIDE NOTE: Be prepared – this stuff will start drying within 2 minutes of mixing so make sure you only mix a small amount at a time.

hydraulic cement to fix foundation cracks

After mixing the cement, I took the spray bottle and sprayed some water into the cracks, only dampening the cracks (NO pools of water). The water will help the cement adhere to the foundation.

fixing cracks in foundation

I then took my trowel and applied the cement to the foundation. While I did this, I applied pressure to the open area to push the cement into the crack.

I continued doing this until all the cement was used or it was too hard to apply. 

TIP: Do not add more water to the cement that is already mixed to the manufacturer’s instructions – this may prevent the cement from hardening correctly!

SIDE NOTE: If you are wondering how to properly mix concrete, or cement, The Family Handyman has a fantastic article on this. 

Next, I mixed another batch of cement and repeated the process until all the cracks/holes were filled in the foundation.

waterproof cracks in basement walls


The most important thing you need to do now is to keep the cement damp (with water) for 24 hours. So, every few hours, I took the spray bottle and sprayed the area. 

By doing this, it will help the cement dry more evenly and help so it doesn’t crack as it dries.

After 24 hours, the cement had dried properly and my foundation cracks were all repaired (well, the ones in this area, at least). 


Then, I applied a coat of Drylock to the wall (over the repaired area) to help waterproof it even more. 

SIDE NOTE: I have used both Drylock and the Behr Masonary Waterproofer and I liked how the Drylock applied to the surface better.

If you are wondering how much this would cost, it would be about $20 and that is the cost of a trowel.

SIDE NOTE: You can see a full tutorial on how to paint cement or cinder block wall in a basement

And that is how to repair and waterproof a foundation by fixing the cracks in a foundation. It’s best to do these easy repairs now, when you first notice the cracks, rather than dealing with serious issues later.

waterproof foundation cracks



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  1. We just had to do this, but we went to the outside. We cleaned off with a wire brush and sealed with tar and a netting, applied Glace ice and water shield, tarred edges, and tarred again the next day and filled our hole back in. We no longer have water coming in!

    1. Hi Rachelle!!! I miss you girl! We did the tar on the outside in one place also. But we did not use the netting or water shield, I really like how you used that. If I ever have to do that again I am going to try that. Thanks for the tip!! Hope your doing well!

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