Concrete Crack Repair Methods


Applied Technologies has been supplying the waterproofing industry since 1998 with quality concrete crack repair materials and equipment. This includes concrete cracks in foundations, retaining walls and concrete slabs. Use this page as a guide to help you decide which repair method is best for your concrete crack.  This section covers cracks such as hairline, actively leaking, structural, slab cracks or a floor crack in a concrete basement.  Read on to learn the best concrete repair method.

Concrete Foundation Crack Repair

The best way to repair a concrete crack in a foundation wall is by injecting it from the inside.  The repair is quick and is therefore inexpensive.  Injection ports are attached to the surface and a paste is applied over the crack surface.  This cures and forms a strong seal to hold the injected epoxy or polyurethane in place.  Then the liquid epoxy or polyurethane resin is injected into the crack.  Once inside the crack, the soil on the exterior and the surface paste on the interior holds the liquids in place as they react.  And then the repair is complete!

Concrete Foundation Crack Repair: Polyurethane Injection vs Epoxy Injection

By far the number one question our new customers ask is "Should I use epoxy or polyurethane foam to fix my basement crack?"  The vast majority of cracks in a foundation wall that leak water should be repaired using a urethane foam. This is for several reasons.

  1. More economical than epoxies
  2. Easier to use
  3. Cure faster
  4. Expand and fill voids
  5. Most cracks do not need re-enforcing from epoxies

Polyurethane Foams

Urethanes react with moisture in the crack to foam and expand inside the wall.  This completely fills the void from top to bottom and all the way through. In fact, the urethanes can expand up to 30x their initial volume.  Urethane foams are flexible and move with the expansion and contraction of a foundation wall from freeze/thaw cycles.  Much less resin is needed with urethane foams since they expand in volume.  That makes them much more economical than epoxies.  Finally, urethane injection is relatively easier to do than an epoxy injection.

Polyurethanes Pros

  • Less expensive
  • Easier to use than epoxies
  • Inject actively leaking cracks
  • Fills larger width cracks
  • Flexible

Polyurethane Cons

  • Not a structural repair

Polyurethane Foundation Crack Repair Kits

Polyurethane Resins


Epoxies weld the crack together and restore structural strength.  The bond strength can be much higher than concrete.  Movement is eliminated in the concrete wall during expansion and contraction cycles.

Foundations that are moving or have a continuing stress load on them may need additional repair methods to stabilize the wall and prevent further damage.  The epoxy is stronger than the concrete, but the continued stress load may cause the concrete to crack again.

Epoxy Pros

  • High strength weld
  • Stronger than concrete
  • Structural repair of crack

Epoxy Cons

  • More expensive than urethanes
  • Bond strength is lower when done in a wet crack
  • Concrete can re-crack if the wall is still moving

Epoxy Concrete Basement Crack Repair Kits

Epoxy Materials

Structural crack that 
has deflected inwardStructural crack that
has deflected inward
Is the Foundation Crack a Structural Defect?

Nearly 100% of concrete foundations crack.  This is because as the concrete cures, it shrinks in volume.  This shrinkage causes stress on the concrete and to relieve that stress, it cracks.  This is okay and the foundation is designed to handle the crack.  The most common places on a foundation wall where this occurs at the corner of a window, where the wall "steps down" or in the middle of a long wall.  These cracks are nearly vertical in nature and usually 1/2" or less. We recommend using a urethane foam for these cracks.

For a crack that is horizontal, runs at 45 degrees or less, or the wall has deflected, it can be assumed that the crack is structural and an epoxy should be used.  The epoxy will restore the strength of the concrete wall.  Please remember that cracks greater than 3/4" wide, horizontal or have deflection indicate that there is a stress on the foundation that must be remedied.  Even though the epoxy will restore the concrete's strength, the stress may be more than any epoxy can withstand.  Contact a foundation repair contractor who can install steel I-beams to completely restore the wall.

Low Pressure or High Pressure Injection for Concrete Cracks

Low pressure injection using surface mounted ports, single or dual cartridge resin cartridges and a hand trigger injection gun is the most common method to repair a crack.  Professional waterproofing contractors know that this system works for 90% of cracks that they encounter. 

Where to use low pressure

  • Wider than hairline (wider than a fingernail or 1/32")
  • Surface of the wall is dry (it can be damp, but not wet)

Low pressure injection polyurethane kits             Low pressure injection epoxy kits

High pressure injection uses drill in place packers to get the resin into the crack.  A grease gun filled with resin is attached to the packer.  This process is used on actively leaking, hairline or cracks that have already been filled with hydraulic cement.  Higher pressures are needed to get into a hairline crack than a trigger injection gun can generate.  Also, water on the wall surface from actively leaking cracks will not allow the surface paste used with low pressure systems to adhere to the concrete. 

Where to use high pressure

  • Narrower than hairline (less than fingernail thick)
  • Actively leaking water
  • Previously repaired cracks

High pressure injection kit

Actively Leaking Concrete Basement CracksActively Leaking Concrete Basement Cracks

A foundation crack that is actively leaking water can only be repaired by using a polyurethane foam.  They set up much faster than an epoxy so the water will not push all of the resin out before it has cured and expanded.

Our Acta-Leak Concrete Crack Repair Kit will stop the water from coming in a basement.

Because the surface of the concrete wall is wet, a surface paste cannot be used to adhere ports or to keep the resin in the crack as it reacts.  But it is still possible to perform the repair by using the high pressure method. 

Holes are drilled alongside of the crack and packers are inserted.  The polyurethane resin is then placed into a grease gun.  The grease gun is attached to the packers and the resin is pumped into the crack.  On contact with water the polyurethane will begin to foam and expand, stopping the water.

Hairline Concrete Wall Crack Injection

At Applied Technologies we define a basement crack as "hairline" if you cannot get a fingernail into it.  Cracks as narrow as this can let in water.  A low pressure injection using a manual dispensing gun may or may not be able to generate enough pressure to get the resins into the crack. A good tip on injecting them by low pressure is to warm the cartridges in water.  This will make the resin thinner and more likely to enter the hairline crack.

For cracks that are extremely narrow, the high pressure system can be used to repair these cracks.  This is done by drilling packers into the wall and using a grease gun loaded with resin to inject the materials.  The grease gun method can generate much higher pumping pressures to get the resins into the crack.

The Acta-Leak Concrete Crack Repair Kit will repair hairline cracks.

Previously Repaired Basement CracksPreviously Repaired Basement Cracks

If your foundation crack was repaired previously by hydraulic cement, it is still possible to inject a urethane foam.  The technician who first fixed the leak chiseled a vee-notch in the wall and then packed it with cement. Applied Technologies does not recommend you chisel out this cement.

Low pressure injection can be done if there are gaps in the hydraulic cement.  If not, then the best and most efficent method is to do a high pressure injection.  This is because you leave the cement in place and drill the packers so that they intersect the crack behind the repair.  Please see the high-pressure crack repair section for more information.

Concrete Floor Cracks

Cracks in a basement's concrete floor cannot be repaired using epoxy or urethane injection.  This is because the resins will flow out of the crack and into the gravel below before they will cure.  Please refer to our Crack-Tite concrete slab and floor repair kit for a solution.

Basement Wall to Floor Seam Leak

It is common for the seam formed where the slab meets the wall to leak.  This water usually is coming up from below the floor due to the water table rising after rains.  Injecting a urethane foam into this seam will stop the water in the area it is injected into.  However, we DO NOT recommend injecting urethane foams of any type or manufacturer into this seam.  This is because if the water is not able to enter the basement area, high water pressures can develop that causes a structural problem in the concrete slab or wall. A functioning drain tile and/or sump pump system is required for a proper long term solution for this problem.

Concrete Block Walls and Injection

Unfortunately, because a concrete block is hollow, it is not possible to inject a polyurethane or epoxy into them to seal off the crack.