How to Fix Foundation Cracks

Concrete cracks. That’s a fact of construction life that has been with the human race since it began building with concrete three millenia ago. The problem spurred the Romans to develop and perfect a self-healing concrete that incorporated crystalline calcium. When a hairline crack formed in Roman concrete, and water gained entry through it, the water and calcium mixed, forming a crack-filling sealer. This stops the leak and halts further degradation. Modern concrete, good as it is, lacks this feature, so its cracks worsen over time as water comes and goes through it. The problem affects everybody, from homeowners, to farmers, to the engineers in charge of maintaining bridges, dams and waterworks.

Given the widespread nature of the problem, it’s no surprise that Popular Mechanics is also burdened by it. The century-old building we occupy in downtown Easton, Pennsylvania, has a foundation and walls that are thoroughly cracked. But cracking concrete has met its match, and you don’t have to be an engineer­–Roman or otherwise– to fix the problem.

Crack Repair, Start to Finish

In the case of our building, help arrived in the form of a local contractor, Anthony DeFranco and his employee, Juan Rivera. DeFranco demonstrated the repair method using ordinary tools and a specialized leak-sealant from Seal Boss. We were amazed at the simplicity of the process and the good results it produced–we haven’t seen any further leaks through the foundation since the two men completed their work.

To fill and seal cracked concrete, you drill holes along the crack and insert injection ports (called packers) into the holes. Next, into the holes you inject an expanding liquid polyurethane resin mixed with liquid catalyst called accelerator. The crack-filling material expands as it cures, sealing the crack and preventing further water entry. Here’s the process, start to finish.

DeFranco made a series of X-shaped marks along the crack to mark the location of holes he would drill. He then used a Metabo-HPT rotary hammer to make a 1/2-inch diameter hole on each X.

Next, DeFranco cleaned each hole with a small 1/2-inch diameter brush, removing dust and concrete chips to allow full penetration of the leak-stopping polyurethane resin that he pumped into each hole.

DeFranco and his employee Juan Rivera started at one end of the wall and inserted an injection port, called a packer, into each hole. The packer consists of an aluminum body with a rubber-sleeved tip and a Zerk fitting into which the men pumped polyurethane resin. The rubber sleeve provides a seal against the wall of the hole, even despite many hundreds of pounds of hydraulic force created from pumping the resin through the packer into the hole.

Rivera pushed a packer into a hole and with a few careful hammer taps set it in place for further tightening.

Rivera placed a deep socket over the body of the packer and tightened it. This expands the packer making a tight seal against its rubber tip and the body of the hole. Once tightened, the packer is ready for injection of crack-filling material.

DeFranco and Rivera mixed Seal Boss Water Stop Foam and 15X Accelerator (a catalyst) at a ratio specified by its manufacturer to suit the specifics of the job, such as the width of the crack and whether the crack is actively leaking water at the time of the application.

DeFranco mixed the polyurethane resin and accelerator at the correct ratio, then poured the mixture into the back of the applicator, and poured the polyurethane resin into the manual applicator. After the tool was filled, he primed its pump by working the lever several times. In the course of pump priming, the excess crack-filling resin squirted out of the applicator and into a plastic bucket on the tailgate of his truck.

DeFranco and Rivera pre-moistened each injection hole with some water supplied by a garden sprayer then fitted the tip of the applicator pump onto the Zerk fitting on the end of the packer. With some forceful work on the applicator’s lever, they pumped in a mixture of Seal Boss Water Stop Foam and 15X accelerator into the hole. They stopped pumping when the material began to ooze out of the crack. Then they moved onto filling the next packer.

The polyurethane foam and catalyst accelerator react together and with water, forming a closed-cell plastic that fills the crack and resists further water incursion. The excess material simply drains down the wall or, in the case of lower holes, onto the floor.

After the water-stopping material has hardened into a plastic foam, the contractors removed it from the wall and floor with putty knives and scrapers. They removed the packer with a socket and socket wrench, then filled the remaining hole with mortar. With that, the job is complete.

Roy Berendsohn

Senior Home Editor

Roy Berendsohn has worked for more than 25 years at Popular Mechanics, where he has written on carpentry, masonry, painting, plumbing, electrical, woodworking, blacksmithing, welding, lawn care, chainsaw use, and outdoor power equipment. When he’s not working on his own house, he volunteers with Sovereign Grace Church doing home repair for families in rural, suburban and urban locations throughout central and southern New Jersey.