DIY Concrete Leveling: What You Can Fix Yourself and What You Shouldn't

It's Saturday, the back walk has a lip on it again, and there's a hammer drill in the garage. A few videos make lifting concrete look like a two-beer project.

Some of it is. Plenty of concrete problems are within reach of a handy homeowner, and we'd rather you fix those yourself than pay anybody.

The trick is knowing which problem you have. "Leveling" covers several different jobs, and only one of them involves lifting anything.

First: What Are You Actually Trying to Fix?

Pick the wrong tool and you can spend a weekend making the problem harder to fix. The classic example is pouring self-leveler over a slab that sank.

Go Ahead and DIY These

These are honest homeowner jobs. You don't need us for any of them.

• ✓Pavers and stepping stones. Pull the sunken ones, scrape out the old bedding, add and tamp base material until it's firm, screed a thin layer of sand, and set the paver back a hair high so it settles in.
• ✓Plastic or composite AC pads. These get re-leveled with compacted gravel underneath. The pad is easy. The refrigerant lines attached to the unit are the delicate part, so plenty of people have their HVAC company do it at a tune-up.
• ✓Patching chips and small holes. Vinyl or polymer-modified patch products feather out well on small damaged spots. Read the bag for traffic times. Some want a full day before you walk on them and longer before you drive on them.
• ✓Sealing cracks and joints. A self-leveling polyurethane sealant in a caulk gun does a good job on horizontal joints and cracks. Clean out the crack first, use backer rod in anything deep, and don't fill a joint flush with dirt still in it. (If you'd rather skip it, we caulk joints, cracks, and the gap where concrete meets the house, and it's easy to add right after a lift.)
• ✓Fixing the water. This one does more than any product on the shelf. Extend downspouts several feet past the slab, point sump discharge away from concrete, and build soil up along slab edges so water runs away instead of underneath. In northeast Wisconsin, spring snowmelt does most of the damage, so do it before the next thaw.

Maybe: Small Jobs With a Real Learning Curve

Jack-and-pack on small, light slabs

The idea is simple: pry or jack up one edge, pack gravel or sand under it, and set it back down.

It works on a stepping pad or a small landing. The limit is weight. Normal concrete weighs roughly 145 pounds per cubic foot, so a 3-by-3-foot pad, 4 inches thick, is around 435 pounds. A 4-by-4-foot sidewalk square at the same thickness is closer to 775. Lever one edge of that and the slab is trying to bend, which concrete doesn't do. It cracks.

If you try it:

• ✓Lift evenly and slowly, using a long board as a spreader so you're not point-loading one corner.
• ✓Never put your hands or feet under a raised slab. Block it with lumber as you go.
• ✓Pack, tamp, and repeat. Loose material dumped in settles fast, and you'll be back at it next spring.

Consumer foam lifting kits

These exist: small two-part polyurethane kits sold for lifting a single sidewalk square, a step, or a small pad, or for filling voids. You drill holes, set injection ports, and dispense foam that mixes, expands, and hardens under the slab. They run at much lower pressure and volume than professional equipment. Some are marketed to homeowners, and others are sold mostly to contractors with training recommended.

What to know before you buy one:

• ✓They're sized for small areas. They're not built for driveway panels, garage approaches, or big patios.
• ✓The chemicals need respect. One component is hazardous until it cures. Wear chemical-resistant gloves, eye protection, and a proper respirator, and follow the safety sheet that comes with the kit.
• ✓Temperature matters. Cold chemicals don't react properly. Late-fall Wisconsin mornings can be too cold even when the afternoon feels fine.
• ✓You get one shot. Once foam hardens, it's there. A slab you over-lift stays over-lifted.

And skip the cans of expanding gap filler from the insulation aisle. That's made for sealing gaps around windows, and it's nowhere near firm enough to hold up a slab.

Where DIY Lifting Goes Wrong

These are the common mistakes, and they're the same whether you're using a jack or a foam kit:

• ✓Over-lifting. Foam keeps expanding for a bit after you stop injecting. Push one more shot because it "looks almost there" and the slab ends up high. Foam can't lower concrete, so the usual fix is cutting the slab out.
• ✓Cracking the slab. Lift one corner too far, too fast, and a slab that's tight against its neighbor, the foundation, or a step will snap. Small increments, rotating between holes, is the whole game.
• ✓Not knowing where the void is. The empty space often isn't where the slab looks lowest. Tap it with a hammer or drag a chain across it: solid concrete rings, hollow spots sound dull.
• ✓Too few holes. One or two holes can leave the slab sitting on a lump of foam with hollow space around it. It looks level until you stand on the edge.
• ✓Foam escaping. Foam takes the easiest path: out through cracks and joints, under the neighboring slab, into the lawn, or along a gap toward the foundation, a window well, or drain tile. Next to the house, that last one is the expensive surprise.
• ✓Concrete dust. Drilling concrete makes fine silica dust, and OSHA warns breathing it over time can permanently damage your lungs. Use a vacuum attachment or water, and wear a respirator.

Why Self-Leveling Compound Isn't a Lift

Self-leveling compound and resurfacer are overlays. They're a thin layer of cement-based material that flows over the top of the slab. They're great at smoothing a rough surface or filling shallow low spots on a slab that hasn't moved. They don't raise anything.

The numbers make it clear. A common bagged resurfacer goes on from a feather edge up to about 1/2". A common self-leveling floor product maxes out around 5/8" per layer and is labeled indoor-only. A walk that dropped an inch and a half needs a lift, not a pour.

Build it up in layers anyway and the void underneath is still there. When the slab moves again over a Wisconsin winter, the thin layer on top cracks with it.

Good use: a garage or basement floor with a rough surface or a shallow birdbath, on a slab that's stable. Bad use: a sidewalk square that sank, or a slab that rocks.

DIY or Call Someone?

A Quick Self-Check Before You Buy Anything

1. 1Did it sink, or is the surface just rough?Sinking means lifting. Rough means patch or resurface.
2. 2How big is it?Bigger than a stepping pad or one small square is a hard DIY lift.
3. 3Is it touching the house?Think twice before injecting anything there.
4. 4Is it solid?A slab in pieces won't lift as one unit no matter who does it.
5. 5Where's the water coming from?Fix that first. It helps whatever you do next.