Epoxy vs. polyurethanes in repairing concrete cracks
When repairing concrete cracks, which material is considered better, structural epoxy or polyurethane? Both materials can accomplish the task and the applicator only needs to make use of the material which he has more experience using. However, if the cracks need to be structurally repaired and the area needs to be stronger than concrete around it, epoxy is a better option. If the reason why the crack has to be repaired is to prevent water leakage or if the crack is actively leaking, polyurethane is the better choice. Structural epoxy for crack injection is available in different viscosities from ultra-thin to the paste-like so that cracks of varying widths can be accommodated.
The main advantage of structural epoxy when repairing cracks is its amazing compression strength which often exceeds that of concrete but epoxies take time to cure usually taking hours to harden. This can be an advantage since epoxy can flow into the smallest crevices but epoxy can flow out of the backside of the crack before it has hardened once the backfill outside the wall has separated from the foundation. If there is concern about material leaking from the back of the crack, polyurethane can be used but it will not provide the same compressive strength that epoxy does. The real benefit of polyurethane is its expansion ability to fill in any void areas in the crack.
Why the choice between structural epoxy and polyurethane usually depends on the applicator
Applicators will tend to work with materials they are familiar with and typically polyurethane is more user-friendly. For the typical wet and leaking foundation crack without any structural risk in the foundation, an injection of polyurethane foam can fix the crack. When the foundation’s structural integrity is compromised by a large/wide crack or there is a buildup of multiple cracks in the same area, contractors will suggest that structural epoxy be used because it is significantly stronger than the existing foundation wall. Structural cracks typically result from wall movement due to thermal changes, uneven loading and settling of the footing, soil pressure or soil shrinkage which can compromise the structural integrity of the foundation. If the areas around the foundation continue to experience soil settlement especially in colder climates, structural epoxy may not be sufficient to repair the cracks and further reinforcement might be necessary.