What Is Used for Cracked & Leaking Cement?

Epoxy

• Epoxy and latex concrete patch formulas are available at most hardware stores to use as a waterproof coating on concrete surfaces and for small patch repairs for hairline cracks less than 1/8 inch. Epoxies create a strong, rigid seal but take a long time to cure. If the surface is wet, the epoxy may run out the opposite side of the crack before hardening, making the patch useless.

Caulk

• Caulk is often used to repair small cracks in concrete walls, but it provides only a surface patch. Water will still seep through the crack, and efflorescence, combined with the pressure of the water, can cause caulk to peel away eventually. At best, caulk is a temporary repair for minor leaks and will have to be reapplied approximately every six months to a year.

Mortar

• Mortar is ideal for filling in holes and cracks larger than 1/8 inch where leakage is minimal. Mortar used to patch concrete typically consists of one part cement, two parts sand and enough water to create a stiff mixture. For cracks that are leaking, the mortar is pushed into the crack with a trowel or putty knife. Often, the crack is enlarged by chipping out a dovetail groove along the length of the crack before the mortar is applied. This gives a better surface for the mortar to adhere to.

Hydraulic Cement

• Large cracks in concrete may also be repaired with hydraulic cement. An inverted V-shaped groove is first chiseled into the cracked area, and then the hydraulic cement is applied. This provides a rigid plug, but hydraulic cement may not hold its bond as temperature and moisture levels fluctuate. Hydraulic cement patches typically last about two years before efflorescence forms around the area, allowing water to pass through, which may push out the plug.

Urethane and Polyurethane Polymers

• Urethane is sometimes used to seal small hairline cracks in concrete because it sets fast enough to seal the crack without running out the other side. It is slightly flexible, and may last longer than other options, but a hairline crack can expand to almost twice its original size. If this happens, urethane may not be strong enough to hold the seal. Leaking hairline cracks can also be effectively sealed with a high-viscosity polyurethane polymer, which bonds well to concrete that is wet. This material can expand up to 20 times its volume, so expansion will not cause the seal to fail during the natural expansion and contraction of the concrete.

Waterproofing

• Concrete walls that seep moisture but have no visible cracks or holes can be sealed using a latex or epoxy waterproofing compound designed for concrete surfaces. If your walls have cracks or holes, once they’re patched or repaired, the coating can be applied later. Waterproofing compounds are typically sold as a powder that is mixed with water and then brushed or rolled on a premoistened wall. Waterproof compounds will not usually adhere to painted concrete. These surfaces must be cleaned of all paint and sanded before the waterproofing is applied.