Concrete Joint and Crack Sealing: Closing Gaps to Protect the Slab Below

An open joint or crack is a direct path for rainwater to run down into the soil beneath the slab. In the Carolinas that matters because water washing under flatwork erodes the supporting subgrade, which is one of the ways a slab starts to settle, and in winter freezing and thawing swings, trapped water can expand and widen a crack further. Sealing closes that path, helps keep the soil beneath the slab stable, and stops dirt and weeds from collecting in the gaps. It is a protective step as much as a cosmetic one.

Not on its own. Sealing protects the gap and keeps water out of it, but it does not change the force underneath the slab. In the Piedmont, that force is often clay soil swelling and shrinking against the slab through wet and dry seasons. In the Sandhills or along the coast it is often sandy soil and water washing out the subgrade. If a crack is from active soil movement or the slab has already settled, sealing is one part of a plan, and we may recommend leveling the slab first so the seal holds.

We use a flexible joint sealant, commonly a polyurethane, chosen to match the width of the gap and whether it moves. Flexibility is the whole point. Control joints exist because concrete expands, contracts, and shifts with temperature and soil moisture, so a rigid filler would simply crack again at the next seasonal swing. A flexible sealant stretches and compresses as the joint opens and closes through the Piedmont's wet and dry cycles or a slab's daily temperature change, which is what lets the seal last. We confirm the right material for your slab during the inspection.

There is no set price, because the cost follows the scope of the work. It depends on the total length of the joints and cracks, how wide and deep they are, the condition and access of the slab, and the sealant used. Where a slab has settled, leveling may be recommended alongside the sealing. The free inspection finds the cause, and you receive a written estimate at no cost before any work is scheduled.

How concrete leveling services are priced

Some cracks need more than sealing, and this is where an inspection matters. Sealing is well suited to narrow, stable cracks and open control joints in a slab that is still sound. A crack that is actively widening, a slab that has settled or lifted unevenly, or cracking that traces back to soil movement is a sign of something underneath that sealing alone will not fix. In those cases we will tell you plainly what is going on and what we would recommend, whether that is leveling or a deeper structural evaluation.