what is slurry?

How Is Slurry Used In Foundation Repair, Concrete Repair, & Under-Slab Tunneling?

What is slurry and how is it used? Simple questions. I am hoping the answer is that Slurry is the newest frosty treat available at your local drive-in diner, but I am probably wrong. Yep . . . my boss says I am definitely wrong . . . bummer.

Slurry is a silly and fun-sounding word but it actually is a useful tool in foundation repair, as well as concrete repair, and under-slab tunneling

Anchor Foundation Repair

At Anchor Foundation Repair, we use slurry in all three of these applications and have been for nearly 25 years. We can explain what slurry is and how it is used because we have used it thousands of times in providing repair services to homeowners in Bryan, College Station, and surrounding Brazos Valley communities.

We will explain what slurry is and how and why it is commonly used in various home repair applications. So put on your parka and let’s explore this chilly dairy dessert . . . oh sorry, still wrong about that part . . . 

Ok, let’s check out the real story about slurry, and not my made-up one (still a little bummed though but I will try to power through for you).

What Is Slurry? What is Slurry Used For?

Portland cement is used in making slurry

Slurry is a mixture of topsoil, Portland cement, and water. Specific to our area, we use a Brazos River topsoil that is sifted and fine-filtered before mixing with the cement and water. The topsoil choice should be tailored to your area if you’re not here in the Brazos Valley.

If slurry sounds a little bit like mud, that’s because it IS a little bit like mud. The consistency of the slurry is different depending on its purpose in the repair project. The slurry is made thinner and more watery for filling purposes and thicker and with less water for lifting purposes.

We’ve already mentioned that slurry is used in foundation repair, under-slab tunneling, and concrete repair. So in foundation repair and under-slab tunneling, slurry is used as a filling material and is of a thinner consistency like pancake batter. In concrete repair, it is used as a lifting agent and is more of a cookie dough consistency. Yum!

How Slurry is Used in Foundation Repair

Slurry is used in foundation repair as a finishing step in the drilled bell-bottom pier repair method. This step is called mud-pumping and it is commonly used with drilled piers but not necessarily with all other methods of foundation repair. Mud-pumping is used to fill the void under your home created by raising the slab-on-grade foundation up to its proper elevation.

What happens in foundation repair is that your home has sunk and needs to be lifted back up. The home and the soil underneath your home have settled and caused foundation settlement

Once the home is raised, there is now some empty space between the majority of the underside of the foundation and the ground (except where the piers are holding it up). Mud-pumping this void under the home with slurry will fill up that space completely.

slurry used in mud-pumping

Slurry is pumped under the home by some temporary piping laid in place by the foundation repair team. They use a little hydraulic pumping machine to pressurize the slurry and inject it under the home through these pipes. Then the temporary pipes are removed. The slurry dries to a hard sandstone-like texture that is very strong and can bear considerable weight.

Benefits of Slurry Used in Foundation Repair

Mud-pumping slurry to fill the void under your raised home has many benefits. The first is that it fills that space up with something. If it isn’t filled with something purposeful, it can get filled with other undesirable things, like water or critters, or both!

void under raised foundation is filled with slurry

Speaking of water under your home, if that void under your home fills with seeping water, then erosion can occur which leads to more settlement. We don’t want that, right?! So the use of slurry mud-pumped under your home helps to prevent erosion and washout.

Preventing erosion, washout, and filling the space for extra support under the entire surface of the foundation ultimately helps to minimize the opportunity for future settlement of the home. In other words, filling up that space and giving the home more support is the best way to lock in your foundation repair and make it as secure as possible.

Maybe another way to think of it is this: you’re packing a box to send in the mail. You fill the box with whatever item and then add some padding but not really enough to fill the box entirely. The top surface of the box represents your foundation.

If you leave a void of empty space inside the top of the box, then the box can get crushed and smushed in the mail. Filling it all the way up is the best way to keep your items safe, secure, and help them stay in place during shipping.

The same is true for your foundation repair in a sense. Leaving the void empty opens up opportunities for things to go wrong. And filing that void can avoid them. See what I did there?

How Slurry is Used in Under-Slab Tunneling

Under-slab tunneling is a way to get to plumbing problems under your slab foundation. Tunneling is a less messy and less disruptive solution to jack-hammering through your foundation from above to fix an under-slab plumbing issue. Sometimes under-slab tunneling is used along with foundation repairs but it can also be done on its own just to repair plumbing lines under a home.

A tunnel is a 3 foot by 3 foot square tunnel dug in the ground under your home to reach whatever plumbing location needs repairs. It’s made big enough for a plumber to crawl in there and fix your plumbing from below. 

Afterward, the tunnel needs to be filled back in with fresh soil and mud-pumping in slurry helps to completely fill in all the air gaps and extra spaces that were created by the tunnel. 

slurry is used in under-slab tunneling

The slurry is mud-pumped under your home in the filled-in tunnel the same way as with foundation repair. Temporary pipes are set up, and the slurry is pressurized and pumped under the home with the pumping machine. Then the pipes are removed and the slurry hardens to a firm solid material.

Benefits of Slurry Used in Under-Slab Tunneling

Mud-pumping slurry with under-slab tunneling has similar benefits to foundation repairs. The slurry fills up all the space and minimizes opportunities for future settlement because of the remnants of a tunnel being dug under the home.

Another similar benefit to foundation repair is to help prevent erosion and washout in the former tunnel area.

An extra benefit for tunneling and plumbing repairs is that the slurry also helps to secure and lock in the position of the plumbing drain lines at the proper pitch. Plumbing drain lines are carefully sloped to ensure that they drain the *bad water and stuff* away from your home.

Using slurry makes sure that the pipes don’t shift or come out of alignment from how they were installed after the repair. 

How Slurry is Used in Concrete Repair

Slurry for concrete repair is used for lifting sunken concrete slabs back to their original elevation and slope. This method has a name and it’s called mud jacking. Hooray for more fun names . . . 

mud-jacking is like jacking up a car

Mud jacking is a form of concrete repair that lifts a concrete surface from below by injecting slurry underneath the slab of concrete using holes drilled through it. The slurry is pumped in using the same pumping machine only at a higher pressure setting. The slurry jacks up the concrete to the desired position, similar to a car jack lifting a car for changing a flat tire.

The slurry fills in the area under the slab and also is strong enough to lift because it is a thicker material than used for void filling. 

So the differences between mud jacking and mud-pumping are in the consistency of the mud, the purpose of the slurry (lifting vs. filling), and how the slurry gets where it needs to go (injected from above rather than piped in from below).

At any rate, slurry is used in mud-jacking to lift and hold the concrete back where it’s supposed to be. Mud-jacking concrete that is still in good shape (just crooked) is a great alternative to fully removing and repouring new concrete

Benefits of Slurry Used in Concrete Repair

mud jacking for concrete repair

Using slurry for mud-jacking in concrete repair has many benefits. One is that it is a time and money saver over the full replacement of a sidewalk, driveway, or patio. Mud-jacking uses simple materials that don’t cost much and definitely cost less than the labor and materials for a tear-out and full replacement.

Mud-jacking takes a few hours or a couple of days versus a full replacement which could take a week or more. 

Just like slurry’s other uses, using it in concrete repair minimizes the opportunity for future settlement of the concrete surface and prevents erosion and washout under the concrete slab.

One other benefit of using slurry and mud-jacking is that it’s a more natural material and not a chemical substance. Some people might like that over a similar method that uses the same concept but a different lifting agent.

Are There Alternatives to Slurry?

poly foam injection material

There is an alternative to mud-jacking and it’s called polyjacking. Instead of the slurry used in mud-jacking, polyjacking uses a high-density polyurethane foam product. Polyjacking is used in both foundation repair and concrete repair (but not with under-slab tunnel filling).

Slurry and mud-jacking are great, but polyjacking has some great qualities too, and can be a better fit for homeowners in some cases. We are a fan of polyjacking even though we don’t provide that service (but we like it a lot and might provide it in the future).

At Anchor Foundation Repair, we know there are many options available to homeowners and want you to find the best one for you even if that means going elsewhere for your repairs. After 35+ years in business, we build trusting relationships by being open to and suggesting alternatives when they seem like a better choice for your home and situation.

Check out this article about mud-jacking vs. polyjacking for concrete repair comparisons OR for a deeper dive into how polyjacking can be used in foundation repair, try this one, “What is Polyjacking? The Poly Foam Injection Used in Foundation Repair.