A leak that's still running calls for a different resin than a crack that's dry. Use the wrong one and the water pushes your material back out of the crack, and the homeowner calls you again.

The difference comes down to how each resin reacts with water. Here is how to choose on the job.

The difference in one line

Hydrophilic urethane reacts with water. The moisture in the crack triggers the cure, so it can seal a leak that is still moving. Hydrophobic resins repel water. They need a dry crack and dry surfaces to bond, and once cured they form a rigid fill.

When hydrophilic is the call

Use a water-reactive urethane when water is moving through the crack. Our #900 Hydrophilic Injection Urethane is made for sealing active leaks in foundation walls.

Signs you are on a wet job:

• Water is visible. Damp streaks or a weeping crack count.
• The leak comes back after rain or thaw. Seasonal water movement works against rigid materials.
• The customer needs the water stopped. Stopping the leak is the deliverable, not a structural rebuild.

Hydrophilic urethane is not a surface patch. It goes into the crack through ports, like any injection job, and the water already in the crack drives the reaction.

When hydrophobic is the call

A dry, dormant crack is a fill problem. Choose a resin that stays where you put it and cures rigid. For this, width decides the product more than moisture does.

• Tight hairline: a thin, penetrating resin like our #700 Super Low Viscosity Urethane.
• Wider dormant crack: a resin with body, like our #1001 High Viscosity Injection Epoxy, so the void fills instead of just coating the faces.

The mistake that causes callbacks

Injecting a dry-crack resin into a crack that is actively leaking. It can look fine for a few minutes. Then the water behind it finds the path of least resistance, the bond never develops, and the leak returns.

The reverse error costs time too. A water-reactive resin in a dry crack that is really a structural problem seals the symptom and leaves the cause. If the crack is moving, wide, or the wall is bowing, bring in an engineer before you quote.

Prep matters more on wet work

1. Find every entry point. Water takes the easiest path, so sealing one crack can move the leak to the next.
2. Open the crack face. Loose material and paint stop ports from seating.
3. Set ports and surface seal. Follow the manufacturer's port spacing, and make sure the face seal holds against moisture.
4. Work from the bottom up. Starting low pushes water ahead of the resin instead of trapping it.
5. Check temperature on the data sheet. A cold basement wall changes cure time.

After the leak stops

Sealing the crack stops this water. It does not fix grading, a failed drain tile, or a downspout dumping against the foundation. Tell the customer about the water source before you invoice, so a new leak next spring is not a surprise.

The short version

Wet crack with a running leak: use hydrophilic urethane. Dry, dormant crack: match the resin to the crack width and let it cure rigid.

Shop hydrophilic urethane and the full injection line