There are two tools for a crack in a foundation wall, and they do different jobs. Injection fills the crack. Surface seal protects the face of it. Pick by habit instead of by what the crack is doing, and you either spend material you didn't need or leave the real problem open behind a good-looking finish.

Here's how to decide, in the order you'd actually walk the wall.

What each one does

Crack injection puts material inside the crack through ports and fills the void. It's a repair. It restores the wall's continuity across the crack and stops water from passing through it.

Surface seal is a coating material that closes and protects the crack face. It's not filling the void behind it. Applied properly, it seals the opening and shields the concrete surface from moisture and further deterioration.

If you remember one line: injection is for the crack, surface seal is for the face.

Decide injection when

• The crack is a water path. Water is getting through, the crack is dry and dormant, and the customer wants the passage stopped.
• The crack has depth and width worth filling. A wide crack needs material with body, like our #1001 High Viscosity Injection Epoxy, which is formulated for filling and sealing wider cracks in concrete foundation walls.
• The crack is tight but deep. A hairline still lets water through. A thin, penetrating resin does the work here, like our #700 Super Low Viscosity Urethane.
• The work is vertical or overhead. Then you want a gel that resists sagging, like our #500 Structural Epoxy Gel.

Decide surface seal when

• You're protecting the surface, not filling a void. That's the job our #602 Surface Seal is made for: sealing cracks and protecting concrete foundation surfaces.
• The crack pattern is a map, not a line. A wall covered in fine crazing doesn't have ten cracks to inject. It has one surface condition to seal.
• You need to hold a thin resin in place. This is where the two tools work together, and it's the most common use of surface seal on an injection job.
• The concrete surface itself is the weak point. Sealing and protecting the face is a lower-intervention fix than drilling ports into a wall that doesn't need it.

The part most people get wrong

On a thin-resin injection job, you surface seal the crack face before you inject. Ports go in at the manufacturer's spacing, the face gets sealed, and the resin stays in the crack instead of draining out over the wall while you work. It's a temporary cap as much as a finish.

That's why a truck that carries injection resin but no surface seal ends up improvising a cap, and improvised caps are why thin resin runs down the wall on a Friday afternoon.

When neither one is the answer

If the crack is moving, if the wall is bowing, if the crack runs wider at the top than the bottom, or if the crack is new and growing, you're looking at a structural condition. Injection and surface seal don't fix a wall that's still moving, and selling either as the solution is how a repair turns into a liability. Bring in an engineer before you quote.

There's also a middle option worth knowing: where the goal is sealing and insulating rather than filling, our #551 Polyurethane Rigid Foam covers sealing and insulating foundation and crack repair applications. Different material, different outcome, and worth keeping on the shelf for the jobs it fits.

The walk-the-wall checklist

1. Measure the crack at its widest point.
2. Check moisture. Dry, weeping, or running water.
3. Check movement. Paint a monitor line or ask about seasonal opening and closing.
4. Decide the outcome the customer is paying for. Stop water, protect the surface, or restore the wall.
5. Match the material to that outcome, not to what's left in the truck.
6. Write it down. Product, date, and conditions, so the next visit isn't a guessing game.

The short version

Water moving through a dry, dormant crack: inject it. A surface that needs closing and protecting: seal it. A tight crack you're injecting with thin resin: seal the face first, then inject. And a moving wall is neither job until an engineer has seen it.

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