How to Stop Concrete Basement Crack Leaks With Polyurethane Foam

December 28, 2012

Preparing a concrete crack for polyurethane foam injection


People love their basements. Basements are used as storage areas, rec rooms, entertainment centers and extra living space. It is important that the basement stays dry to protect possessions, stay clean and remain safe from health hazards. Unfortunately, cracks in a basement wall can let in water and cause damage.

The Cause of Concrete Basement Cracks

It is normal for concrete to crack. As a concrete foundation is made, the concrete is poured as a liquid with water mixed in. As the concrete cures, this water is removed. The removal of water causes the concrete to shrink in volume. As the concrete shrinks in volume it develops stresses that are relieved by the concrete cracking. The common term for this type of crack is a "shrinkage crack." They should be less than 3/8" in width.

Where Concrete Basements Crack

Shrinkage cracks will start at the top of the basement wall and eventually go all the way to the floor. The crack will also go all the way through basement wall to the outside. Common areas for a shrinkage crack are in the middle of a long wall, under the corner of basement windows and where the foundation steps down in height. The crack will be vertical or nearly so. Although it is common for cracks under windows and at foundation step downs to run a few degrees from vertical.

How Water Gets Into The Crack

During periods of rain water can get into the crack. This is because the crack goes completely through the wall to the outside. As the soil releases the water it enters the crack and eventually you see it on the inside.

Polyurethane Injection to Stop the Water Leak

The water leak can be easily stopped by injecting a polyurethane foam into the crack. The repair is performed from the inside of the basement. Since the foundation does not need to be excavated on the outside, the repair is an inexpensive process. The repair can be performed by either a professional technician or by the homeowner with a Do-It-Yourself Kit.

The polyurethane is injected into the crack as a liquid. Once inside the crack it will begin to foam and expand. This is the great advantage of using a polyurethane to stop a water leak. The foaming action causes the polyurethane to expand and fill any voids. Once complete the crack will be filled from bottom to top and the entire width of the foundation wall. After curing the foam will seal out any water.

How the Polyurethane Injection is Performed

Step 1. Attach Surface Ports

Plastic injection ports are attached with a special epoxy directly over the crack. These ports are spaced every six to twelve inches.


Step 2. Seal the Crack Surface

Once the ports are attached, the rest of the crack is covered with the same special epoxy. This is not what makes the crack water proof. It merely keeps the polyurethane in the crack as it reacts and foams.

Step 3. Injecting Polyurethane Foam into the Crack

The injection process starts at the lowest surface port. A mixer that attaches to the polyurethane cartridge is inserted into the port. The polyurethane is in a liquid form and flows into the crack. It will flow all the way to the outside surface of the crack. Once you see the polyurethane start to come out of the next port above you stop injecting into the current port and move to the one above. A plug is inserted into the first port to keep the liquid polyurethane from leaking out. Proceed until all of the ports have been injected.


  1. Not for concrete block walls
  2. Not for use on floor cracks

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