How Big Are the Holes for Concrete Lifting?
The holes drilled for polyurethane concrete lifting are about the size of a dime, roughly 5/8 inch across. A typical residential driveway or sidewalk needs somewhere between six and twelve of them, spaced a few feet apart. They are patched with concrete the same day the work is done, and once the patch cures, most homeowners have to look for them to find them.
Key Takeaways
- A 5/8 inch hole is small enough that the drilling itself takes only a few minutes per hole and produces no cracking or spidering in sound concrete.
- Mudjacking requires holes two to three times wider because wet slurry has to be pumped through them, while polyurethane foam expands after injection and needs far less opening.
- Most driveway slabs need one hole every four to six feet, so the number of holes depends on the square footage being lifted rather than on how far the slab has sunk.
- The patch will be lighter than the surrounding concrete at first and darkens toward a closer match over the following year or two.
- The patches never disappear completely, and on smooth-troweled or stamped decorative concrete they stay more visible than they do on a standard broom finish.
- Concrete can be driven on within about an hour of the lift, because the foam reaches full strength in roughly fifteen minutes.
Why the slab has to be drilled at all
The problem with a sunken slab is not the slab. It is the empty space underneath it, left behind when the soil settled, washed out, or compacted after the original pour. The concrete itself is usually fine. It has simply lost the support it was resting on.
Filling that space means getting material underneath a slab that may weigh several thousand pounds and sits flat on the ground on all sides. There is no way in from the edge. The only practical access is straight down through the concrete, which is what the hole is for.
Polyurethane foam is injected through the hole as a liquid. It expands within seconds, spreads into the voids, and lifts the slab back to grade under controlled pressure. Because the material does the expanding after it goes in, the opening only has to be wide enough for the injection port. That is why the hole is dime-sized rather than fist-sized.
How many holes will be in my driveway?
Hole count is driven by the area of concrete being lifted, not by how badly it has sunk. Foam spreads outward from each injection point, so the holes are laid out on a rough grid with one every four to six feet across the settled section.
In practice, that means a sunken garage apron usually takes six to eight holes. A single sunken driveway panel takes four to six. A long stretch of sidewalk leveling takes one every few feet along its length. A large patio or pool deck can take fifteen or more, though those are spread over a much wider area than a driveway.
A slab that has dropped three inches does not need more holes than one that has dropped half an inch. It needs more foam through the same holes.
Where the holes get placed
Placement is decided by where the voids are, and the voids are usually not evenly distributed. On a driveway apron that has tipped toward the garage, the empty space is concentrated at the low end, so the holes cluster there and thin out toward the high side.
Where there is a choice, holes go where they will be least noticeable. Near control joints, along slab edges, and away from the center of a panel are all preferred. On a driveway, that often means the holes sit in a line the eye reads as part of the joint pattern rather than as a row of dots in the middle of the concrete.
What cannot be worked around is the location of the void. If the empty space sits under the middle of a panel, that panel gets drilled in the middle, because injecting from the edge would push foam sideways instead of lifting the section that has dropped.
On a townhome association in Eagan, we lifted [N] garage aprons and [N] sections of shared sidewalk across the property. The aprons had nearly all settled the same direction, toward the garage, because every unit was poured against the same foundation detail. That made the hole layout almost identical from one apron to the next. The sidewalks were the opposite. Voids there followed drainage and downspout runoff, so placement changed section by section depending on where water had been moving under the slab.
How the holes compare to mudjacking
| Polyurethane foam | Mudjacking | |
|---|---|---|
| Hole diameter | About 5/8 inch, roughly a dime | 1 5/8 to 2 inches, roughly a golf ball |
| Typical holes per driveway panel | 4 to 6 | 6 to 10 |
| Why that size | Foam expands after injection | Slurry must be pumped through at volume |
| Patch visibility | Small, fades with weathering | Larger, stays noticeable |
| Time before use | About an hour | 24 to 72 hours |
The hole size is one of several differences between the two methods. If you are still deciding which one your driveway needs, the fuller comparison is in our post on polyjacking versus mudjacking.
How the holes are patched
Once the lift is finished and the slab is back at grade, the crew hand mixes a small batch of concrete and works it into each hole by hand. Mixing on site means the batch can be adjusted to the slab in front of them rather than poured out of a tube at whatever consistency it comes in. Setting it by hand rather than with a trowel lets the crew feather the patch into the existing surface texture, which is most of what determines whether it disappears into the concrete around it.
This happens the same day, as the last step of the job, before the crew leaves. There is no return visit for patching and nothing for the homeowner to fill in later.
The patch is a structural fill, not a cosmetic cap. It seals the hole against water getting down into the slab, which matters in Minnesota where anything that holds water becomes a freeze-thaw problem within a season or two.
What the patches look like afterward
Honestly: visible at first, and then progressively less so.
Fresh concrete is lighter than aged concrete. For the first several weeks the patches read as small pale dots against a darker surface, and they are the most noticeable they will ever be. Over the following months the patch weathers, picks up dirt and traffic, and darkens toward the color of the surrounding slab. After a year or two on an exterior driveway, most patches sit close enough in color that they stop registering unless you are looking for them.
They do not vanish. Anyone who tells you the holes will be invisible is overselling it. What is true is that a dime-sized patch on a driveway is a far smaller visual compromise than a replacement panel that is a completely different color and age from everything around it.
Two surfaces are worth flagging. On a standard broom finish, which is what most Twin Cities driveways and sidewalks have, the surface texture breaks up the eye and the patches blend well. On smooth-troweled interior garage floors or on stamped and colored decorative concrete, there is no texture to hide behind and the patches stay more apparent. For decorative work, that is a real tradeoff worth weighing before the job starts, and it is something to raise during the estimate rather than discover afterward.
We got to check this ourselves at the Eagan association, where we returned [X] later for a second phase of work. The patches from the first round had weathered into the surrounding concrete well enough that you had to be told where to look. On the shared sidewalks, where foot traffic and sprinkler runoff work on the surface constantly, they had blended further than the garage aprons had.
Frequently asked questions
Will drilling crack my concrete?
Not in sound concrete. A 5/8 inch bit removes very little material relative to the slab, and the drilling is done with a rotary hammer that cuts rather than hammers its way through. Concrete that is already badly cracked or crumbling is a separate conversation, since a slab in that condition may not be a good candidate for lifting in the first place.
Can you drill through my heated driveway or over utility lines?
This has to be discussed before work starts. Radiant heat tubing, conduit, and shallow utility runs all change where holes can safely go, and in some cases they rule out lifting a particular section. Tell your estimator about anything embedded in or running under the slab.
How long does the patch take to cure?
It is walkable almost immediately and driveable within about an hour, on the same timeline as the foam itself. Full color development takes considerably longer than structural cure.
Can I paint or stain the patches to match?
You can, and some homeowners do on decorative concrete. Wait at least thirty days for the patch to cure fully before applying any concrete stain, and test the color on one patch before doing the rest.
Do the holes have to go all the way through the slab?
Yes. The point of the hole is to reach the void underneath, so it is drilled through the full thickness of the concrete, typically four to six inches on residential work.
What if the slab settles again later?
Polyurethane foam does not wash out or compress the way soil does, so the fill itself is permanent. If settlement continues, it is because soil outside the treated area is still moving, which usually points to a drainage issue that should be corrected alongside the lifting.
If you have a sunken driveway, apron, sidewalk, or patio in Burnsville, Eagan, Apple Valley, Lakeville, Woodbury, or anywhere in the south and east metro, Benchmark Concrete Raising can tell you how many holes your specific slab would need and where they would go before you commit to anything. Request a free estimate and we will walk the concrete with you.
