Cracks Are THE Eternal Problem Of Concrete…
To begin with thin surface cracks, also called plastic shrinkage cracks, it is important to know these really can not be repaired and the only reason to do anything is aesthetics as they don’t affect the concrete’s performance. To alleviate appearance of the plastic shrinkage cracks, a thin overlay can be placed on top as polishing doesn’t remove plastic shrinkage cracks.
Overlays can also be used to cover other cracks in slabs such as drying shrinkage. Be sure to prepare the surface, which includes bridging over any cracks. and make sure the concrete is sound. Overlays on poor concrete will likely fail if there is settlement due to poor subgrade compaction.
There is another way to “fixing” non-structural cracks — such as shrinkage cracks. You may follow or route the crack out with a crack chaser (or a saw or angle grinder) and fill it with a sealant. The theory is to open the cracks up and create a vertical face to a depth of ¼ to 1 inch. This new joint is then filled with a sealant.
One proven material for crack sealing is a polyurea. These relatively new materials act like epoxies in their ability to adhere to the concrete and can be installed over a wider temperature range and cure quicker. Prime Resins is a great source of information on joint repair sealants. Note that this type of sealant is designed to have a lower bond strength to the edges of the crack or joint to prevent new cracks from forming adjacent to the repair. If the crack or joint moves, the sealant’s bond fails first, and thus not the concrete.