Fix a basement wall that leaks

Steps

Goal: Confirm the symptom, rule out condensation, then isolate the cause—drainage, foundation cracks, or cove joint.

• Check that water appears on the basement wall, not from a pipe or floor flood.
• Good: Water on the wall—proceed to Check when the water appears.
• Bad: Water from a pipe—see how-to-fix-wall-leak. Water from the floor—see fix-basement-floods.

Check when the water appears

Goal: Narrow the source based on timing.

• Does the water come after rain or storms, or at any time? After rain points to drainage or foundation cracks. Anytime can mean condensation or a plumbing leak behind the wall.
• Good: You know the pattern. Proceed to Rule out condensation.
• Bad: Unsure—check both paths.

Rule out condensation

Goal: Confirm it is intrusion, not condensation.

• Touch the wet area. Condensation beads on a cool surface and wipes away; it often appears in summer when humid air hits cool walls. Intrusion feels wet, may drip, and often correlates with rain.
• Run a dehumidifier for 24–48 hours. If the wall stays dry, it was condensation—no sealant needed. Keep humidity below 50%.
• Good: Intrusion confirmed—proceed to Check drainage.
• Bad: Condensation—run dehumidifier; the guide for wall leaks does not apply.

Check drainage

Goal: Confirm gutters, downspouts, and grading direct water away from the foundation.

• Inspect gutters for clogs and downspouts for proper extension. Downspouts should extend at least 4–6 feet from the foundation. See fix-gutter-is-clogged and fix-downspout-overflows.
• Check grading—the ground should slope away from the house at least 1 inch per foot for 5–10 feet. Add soil if needed; do not pile against siding.
• Good: Water flows away from the foundation. Proceed to Locate visible cracks.
• Bad: Fix drainage first—often stops the leak. Retest after the next rain.

Locate visible cracks

Goal: Find where water enters so you can seal or escalate.

• During or after rain, trace where water enters. Look for cracks in the wall, at the cove joint, or at window wells. Use a flashlight.
• Note the size. Small cracks (less than 1/4 inch) can be sealed. Large or widening cracks need a professional.
• Good: You found small cracks—proceed to Seal small cracks.
• Bad: Large or widening cracks, or no visible crack—call a waterproofing professional.

Seal small cracks

Goal: Seal small foundation cracks with hydraulic cement or epoxy.

• Clean the crack with a wire brush. Apply hydraulic cement or epoxy injection per product instructions. For active leaks, use a product designed for wet cracks.
• Do not seal large or widening cracks—call a professional.
• Good: The crack is sealed and no water enters. Confirm during the next rain.
• Bad: The leak persists—call a waterproofing professional.

Check window wells

Goal: Fix window well leaks if water enters there.

• If water enters at a basement window, check that the well has a drain and it is not clogged. Add a window well cover to keep rain out.
• If the well fills with water, the drain may be blocked—clear it or install a new drain.
• Good: No water pooling in the window well.
• Bad: Drain is blocked or missing—clear or install a drain.

When to get help

Call a waterproofing professional if:

• The crack is large or widening.
• You see bowing or settling of the wall.
• Water is flooding.
• Drainage improvements and small crack sealing have not stopped the leak.

Do not seal large cracks yourself—you can mask a serious problem.

Verification

• No water on the wall during or after rain.
• Gutters and downspouts direct water at least 4–6 feet from the foundation.
• Ground slopes away from the house.
• Small cracks are sealed and dry.
• Dehumidifier keeps humidity below 50% if condensation was an issue.