Garage Slab Replacement in Chicago: When to Tear It Out

A garage slab replacement in Chicago makes sense when the slab has moved, when the surface is failing across a wide area, or when the ground under it is the real problem. A floor with a few stable cracks does not need to come out. This article gives you the signs on each side, what drives the decision and the cost, and what to ask about permits and the contractor.

When does a garage slab need to be replaced?

Replace it when one or more of these is true:

• The slab has settled, tilted or heaved. One side is higher than the other, water runs toward the wrong place, or the slab has dropped away from the walls or the door apron. That is movement, and settlement is a listed cause of cracking (ACI). A patch does not stop movement.
• The surface is failing across a wide area. Peeling, flaking and pitting that cover much of the floor. NRMCA says light to moderate scaling can be resurfaced, but severe, progressing scaling may not be feasible to repair (NRMCA).
• The cracks keep growing, or the slab has broken into pieces that move on their own.
• The slab is in several broken sections and the base underneath is soft or washed out.

Repair or resurfacing is usually the answer when cracks are stable, the surface wear is light and the slab sits flat. See which concrete cracks to worry about for how to read yours, and lift or replace a sinking slab if yours has dropped.

Why do garage slabs fail?

Most cracking comes from how the slab was built: missing joints, poor subgrade preparation, watered down concrete, poor finishing, fast moisture loss and weak curing (NRMCA). NRMCA also warns that a vapor retarder directly under a slab raises cracking potential, especially with high slump concrete, and that the subgrade should be compacted with topsoil and soft spots removed (NRMCA). Those are the questions to ask whoever pours a replacement.

Garages add two things to the mix. Cars drag winter slush and road salt inside, and the slab sits right at the door, where water arrives. NRMCA says deicers worsen scaling by raising how saturated the surface stays (NRMCA), and advises hosing off salt tracked in by vehicles when possible and fixing drainage that lets salt solution pool (NRMCA).

What drives the cost of a garage slab replacement?

We do not quote prices in articles. These are the things that move the number:

Ask each contractor to price the same scope so you can compare. How thick the new slab should be is a design question for the contractor and the Department of Buildings: our garage slab thickness article covers what to ask.

What does a replacement involve?

Roughly in this order: the old slab is broken out and hauled away, the base is checked and corrected where it is soft or uneven, forms go in, reinforcement is set if the design calls for it, and the concrete is placed, finished and cured. Joints are cut or tooled so the slab cracks where you want it to. NRMCA's guidance puts control joint spacing at 24 to 36 times the slab thickness, with a maximum of 15 feet (NRMCA). Ask the contractor where the joints will go and how the floor will drain to the door. A slab that is poured over the same soft base, or with no joints, will crack again.

The old problem has to be answered before the new concrete goes in. If water was the cause, the new slab needs a way for it to leave. If the base settled, the new slab needs a better base than the last one had.

Do you need a permit to replace a garage slab in Chicago?

Check with the Department of Buildings before you start. The City's published lists exempt in-kind replacement of a concrete, brick or asphalt parking surface or driveway, and exempt concrete flatwork like sidewalks and patios on private property under certain limits (City of Chicago). A garage floor is not named in those lists, so we cannot tell you from them whether replacing a garage slab needs a permit. The City's basic rule is that a permit is required before most construction and repair work, with a limited set of exemptions, and exempt work must still follow all construction codes (City of Chicago).

On licensing, the City's mason license FAQ notes that a mason license is not required for slab on grade foundations for single story non occupiable structures like sheds and garages, and also lists an owner of a primary residence (single family, or a multifamily of three stories or fewer and six units or fewer, one property per year) among its exceptions (City of Chicago). That is about who can do the work, not about whether a permit is needed. Do not assume one answer covers the other.

How should you hire for it?

Illinois' Home Repair and Remodeling Act applies to residences of one to six units and lists garages among its examples (State of Illinois). For work above the Act's dollar threshold the contractor must give you a written contract or work order stating the total cost and the business name and address (State of Illinois). Get that, plus the scope: demolition, base prep, reinforcement, joints, finish and drainage.

Looking at a garage floor that has settled, cracked or is flaking? Akats pours and replaces concrete in Chicago, and we will tell you if repair is enough. See our concrete service and the Chicago concrete and sidewalk guide.

Common questions

This article explains general rules and common situations in Chicago. It is not legal advice, and City rules change. For a specific property, check with the Chicago Department of Buildings or a licensed professional.