Hydrophilic polyurethanes should always be used to stop water leaks in cracks.
Hydrophilic resins seek out water in a crack. They chase the water and absorb into the tight micro-cracks and pores of the concrete. This gives hydrophilic resins a tenacious bond to the wet concrete.
Hydrophobic resins repel water in a crack. They resist movement towards wet areas and will not absorb into tight micro cracks and pores in the concrete. They may be forced in under pressure, but the water will act as a bond breaker between the polyurethane foam and the concrete resulting in extremely low bond strengths.
Why is bond important?
Concrete expands and contracts with changes in temperature. In the summer temperatures rise, concrete expands, and cracks tighten up. In the winter when temperatures fall, concrete contracts, and cracks open up. Polyurethane foams are designed to seal leaking cracks. If the material does not bond to wet concrete, it is destined to eventually fail during these thermal cycles, particularly during cold weather. The cracks will open up and leave a gap between the concrete and the foam allowing water to seep back through.
But I have used hydrophobic materials before and they stopped the water.
There is no doubt that hydrophobic resins can be effective at stopping water leaks. They will expand and fill up a wet crack as well as most hydrophilic resins. The failure will usually occur a few months after the job is finished.
Do hydrophilic resins shrink in the absence of water?
Some hydrophilic resins will absorb as much water as they come in contact with during the time of initial cure. These resins do a good job of stopping the water leaks, but usually fail if the water table drops. The water they absorbed will evaporate and cause the material to shrink, sometimes resulting in failure.
Our company was designed specifically to eliminate this problem.hydrophilic resins will only absorb as much water as they need to facilitate the reaction during initial cure. The rest of the water is rejected in the same way that hydrophobic resins reject water.