· by Michael Blair, Nashville's Garage Floor
Cracks in a garage slab are extremely common and most are cosmetic. A coating is a thin film and will not span a crack that moves, so what matters is telling static cracks from active ones.
Static versus active
Pencil a line across the crack at each end, write the date beside it, and note the width. Check again after a season, particularly after a wet Middle Tennessee winter.
A crack that does not change can be filled and coated over. One that opens and closes seasonally will reappear through any coating.
How they are repaired
Cracks are chased out to a consistent width, cleaned, and filled with a semi-rigid polyurea or epoxy filler that is then ground flush before coating.
Ordinary concrete patch and caulk are the wrong products — they do not bond well enough or they stay soft and telegraph through.
- Monitor before repairing — mark, date and measure
- Chase out to a consistent width rather than filling as found
- Semi-rigid polyurea or epoxy filler, ground flush
- Control joints are usually filled rather than treated as cracks
- Spalled areas need patching compound, not filler
Control joints
The saw-cut lines in a garage slab are control joints, not cracks — they are deliberate. Most coating systems fill them flush so the floor reads as continuous.
Some installers leave them, which is also legitimate and means any future movement shows in the joint rather than across the field.
When the slab is past coating
Widespread spalling, deep displacement between crack faces, or a slab that has heaved is beyond a coating. A film cannot fix a structural problem.
At that point the options are grinding and an overlay, or replacement, and it is worth an honest assessment before spending on a coating.