Q&A / 

Hydraulic Cement


Portland Cement Shrinks

Many homeowners don't realize that ordinary Portland cement shrinks when it dries. The shrinkage is very little, however it does shrink.

This means that if you patch a crack or a hole, a very tiny leak may form after the cement dries.

Hydraulic Cement EXPANDS

Hydraulic cements do the opposite. They expand as they cure.

The reason they expand is because the powders contain expansive clays such as bentonite and a few others.

Once you add water to these powders the clay starts to puff up ever so much. The best analogy is adding yeast to flour to make bread.

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Larger Size Locked In Place

When the bread is baked, the larger size is permanently locked into place.

The same thing happens with the hydraulic cement. And it happens fast usually within minutes. The Portland cement sets up and the larger volume of the mixture is locked in place permanently.

There are many brands of hydraulic cement. It's a commodity item. CLICK THE PHOTO NOW TO HAVE THIS DELIVERED TO YOUR HOME.

Cold Water Slows Reaction

If you need more working time when you are filling holes, use ice water to mix the hydraulic cement. This cold water slows somewhat the rapid setting time.

Where To Use

In new construction I use hydraulic cement to

  • fill the void areas in foundations around water pipes
  • electric wire sleeves or conduits
  • foundation form holes
  • deep cracks in foundations
  • any hole in a foundation

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Remove Dust

To get the best bonding between the wet hydraulic cement, be sure to get rid of all dust from the surfaces.

Dampen Existing Concrete

You'll also get the best bond if you slightly dampen the concrete that will be in contact with the fresh hydraulic cement.


Author's Note: The following email comment was received from Art, a Cement Manufacturer's Representative in Southern California.

Hi Tim,

I hope you take this in the spirit in which it is intended and that is to just help your site be better. Your definition of a hydraulic cement is misleading. According to ASTM (American Society for Testing & Materials), a hydraulic cement is a cement that creates a chemical reaction when it comes in contact with water (hydration) and will cure under water.

Being a hydraulic cement in itself has nothing to do with expansion, although some hydraulic cements will shrink less than others, but this is due to them being a sulfoaluminate based cement, not a Portland cement and has nothing to do with them being a hydraulic cement. Being a sulfoaluminate cement is also the reason you have the shortened working times.

Art / Cement Mfg. Rep.

CLICK HERE to get FREE & FAST BIDS from local handymen who work with hydraulic cement on a regular basis.

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10 Responses to Hydraulic Cement

  1. This is a question thrown out there to anyone who might have an opinion. My situation is I have an artiesian well. It is approx 110 ft deep. The well is leaking around the outside of the casing and is causing a portion of my yard to revert to a swamp. I have dug around the casing. I have no idea how to stop the seepage and leaking. Appears no one in the business around me has any idea either. I am considerinf buying a few tubs of hydraulic cement from a local Lowes and dumping it in the space between the casing and the hole. I hope it will cure and plug the leak. Anyone care to give an opinion on my probability of success? Or I sure am open to a better idea.

  2. How does the cost of hydraulic cement compare to portland cement? Is hydraulic cement appropriate for use in a patio that will be tied to the foundation of a home? I want to use this as a foundation for a sunroom eventually, but in the interim it will get plenty of rain and moisture.

    Do you know if hydraulic cement will take an acid stain similar to what portland cement takes?

  3. Regarding sulfoaluminate based hydraulic cements, are these a similar formulation to what the Roman's used based on volcanic ash in the flood plains of Vesuvius? I have always read that these roman cements were extraordinarily long-lasting under water, but that they took a long time to set and gain strength. This seems to contradict your statement that today's hydraulic cements set rapidly and you must work with them for 10 to 15 minutes.

  4. Final question: do you happen to know if there is any commercial cement available in USA or Europe that is using a volcanic ask to create a Roman-type hydraulic cement? I'm looking for something that would be extremely durable in a wet environment.

  5. How long is hydraulic cement "good" if stored dry in original packaging? The previous owner left some behind. Being thrifty, I don't want to buy more if this can be used for a small crack.

  6. To seal a crack in a foundation that's leaking water, would you recommend epoxy or hydraulic cement? Having trouble finding a good comparison.

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