Polyurethane injection is similar to epoxy injection. The difference is that the tubes are spaced farther apart and most importantly we do not use polyurethane to inject cracks. Polyurethane is used to inject Cold Joints, Inlet Pipes or in any space that needs to be filled and that is NOT A STRUCTURAL REPAIR. We have seen time and time again cracks that would re¬-crack (or rip) from being injected with polyurethane. Back in the late 90’s, other companies switched to polyurethane because it was cheaper to use.
Most Structural Engineers believe that epoxy is the best material to repair a structural foundation crack. In our opinion, every crack has the potential of becoming a structural problem and that is why we only use epoxy on foundation cracks.
A Cold Joint is when two sections of poured concrete have dried at different times and therefore create a void between the two. This is not considered a structural issue and that is why we use polyurethane in those cases. We often see cold joints when extensions are added to a house, or under the front steps inside the cold room. The front wall of the cold room under the stairs is usually underground and that is why we see this problem a lot in old AND new homes.
Inlet Pipe injections can be around small wires, electrical or plumbing pipes that are inserted through your foundation walls. Water can seep in around them if there is a void. For this type of injection it is just a matter of finding a space between the pipe and the cement to insert an injecting tub and the polyurethane will inject around the entire pipe. If the pipe is larger (4″) it might be necessary to install two injecting tubes.
Water is injected into the tubes first in order for the product to react. It will then expand 16 times its mass so the amount needed isn’t very much. This is why the tubes are spaced farther apart when injecting a cold joint.