Debunking the "Too Heavy" Myth: What Polyurethane Companies Get Wrong About Sand and Clay Concrete Lifting (Mudjacking)

If you've researched concrete lifting, you've probably run across a common talking point from polyurethane foam companies: sand and clay slurry is "too heavy" for the soil beneath your slab, and injecting it will supposedly overload already weak ground and cause the concrete to sink again. At MI Concrete Lifting, we hear this claim a lot — and we think it's worth taking a closer look at, because the full picture tells a very different story.

The Claim

The pitch usually goes something like this: mudjacking slurry weighs around 100 pounds per cubic foot, while polyurethane foam weighs only 2 to 4 pounds per cubic foot. Because the ground supporting a sunken slab is already "failing," the argument goes, adding heavy material will just cause it to fail again — while the nearly weightless foam supposedly won't.

It's a compelling sound bite. It's also missing a crucial piece of context: what does the soil that's already sitting under and around your slab actually weigh?

What the Ground Is Already Made Of

Soil isn't light. According to soil density data compiled from USDA references and geotechnical resources, compacted soil commonly weighs between roughly 90 and 150 pounds per cubic foot, depending on moisture and composition — with wet or clay-heavy soil often landing on the higher end of that range. State transportation specifications, such as Ohio DOT's subgrade compaction standards, target compacted subgrade densities in the neighborhood of 100 to 105 pounds per cubic foot as a normal, workable target for supporting roads and structures.
In other words, sand-and-clay slurry at roughly 100 pounds per cubic foot isn't some unusually heavy foreign substance being forced onto fragile ground. It's in the same general weight class as the native soil already surrounding and supporting the slab — the same soil that holds up your foundation, your driveway, the road you drive on, and buildings all over the world. The "too heavy" argument compares slurry to foam, but conveniently skips the comparison that actually matters: slurry to the ground itself.

What Actually Causes Concrete to Sink

Multiple independent sources on concrete settlement point to the same root causes, and none of them is "the soil can't handle any material at all." Slab settlement is typically traced back to voids and excessive settling of the base from original construction — most often caused by soil erosion from water runoff, poor drainage, insufficient initial compaction, freeze-thaw cycles, or burrowing animals hollowing out space under the slab. The pattern across virtually all of these causes is the same: something removed support from underneath the slab, leaving a void.

That points to the real question a lifting method needs to answer: does it restore genuine, load-bearing support, or does it just fill space?

Solid Ground Is the Standard — Not the Exception

There's a reason concrete contractors compact the subgrade before ever pouring a new slab: a dense, well-compacted base is the industry standard for a stable foundation. When a slab settles, the goal of a repair should be to put that same kind of solid, load-bearing support back underneath it — not to avoid weight altogether.

That's exactly what our sand and clay slurry process does. We inject a carefully controlled mixture of mason sand, bentonite clay and water beneath the slab, filling voids with dense mineral material that mimics the same kind of ground the slab was originally built to sit on. Rather than introducing a synthetic, weightless void-filler, we're restoring the type of solid, compactable support that's been the standard for structures worldwide for as long as we've been building on the ground.

A Fair Comparison, Not an Attack

We're not here to tell you polyurethane foam doesn't work — it has its place, and plenty of companies do quality work with it. But the "your soil is too weak for anything but foam" argument doesn't hold up once you compare slurry's weight to the soil that's already there rather than to foam alone. In the vast majority of soil conditions we work with here in Southeast Michigan, native ground is already carrying loads at or above the density of our slurry mix every single day.

With the current lack of meaningful, long term research on the longevity and breakdown of polyurethane based foams and their potential to add microplastics to our subsoil, we prefer to stick with material that is known to be safe for the soil. Our mix is primarily natural mineral material — sand, bentonite clay and water — rather than an expanding synthetic polymer. For property owners who'd simply rather not introduce additional polyurethane into the soil around their home or business, that's a meaningful, straightforward difference.

The Bottom Line

Concrete sinks because voids form (whether from poor base prep after construction or wash out) and support is lost underneath it — not because the ground can't handle weight. Restoring that support with a dense, mineral-based material that's in the same weight range as the soil already there is a time-tested, structurally sound way to fix the problem. If your driveway, patio, sidewalk or steps have settled, we'd be glad to take a look and let you know honestly whether lifting is the right fit.