Polyurethanes VS.Epoxies

If the crack is leaking, polyurethane chemical grout would be the better choice because epoxies do not perform well where moisture is present. Polyurethane is a fast setting foam product that can stop leaks in as little as 5 seconds. It can also fix hairline cracks and cracks that are a few inches wide. 

Epoxy can be used for cracks in need of structural repair because of the high compressive strengths they have. Some epoxies even have higher strength ratings than concrete. This is why they are the best choice for non-leaking structural cracks.

A few years back I was asked by an engineer to look at a parking garage that had many leaking cracks. It turned out that those cracks were previously repaired with epoxy grout. This is a perfect example of why grouters should not use epoxy in leaking cracks.  As I mentioned earlier, epoxy does not do well in cracks that have moisture in them.  The other mistakes they made were: using a very rigid epoxy without flexibility, and failing to bridge the crack for movement. This is what caused the cracks to leak again.

My recommendation for this problem was a simple. Because the cracks already had epoxy in them, I had the contractor drill through the wall and into the soil. I then had the contractor pump polyurethane chemical grout behind the wall and build a curtain wall of grout behind each crack.  Problem fixed!