How to Fix a Leaking Basement Sump Pit: Step-by-Step Guide

The sump pit is the last line of defense against a flooded basement. If the pit liner itself develops a crack, water can bypass the pump intake and seep into the surrounding floor or worse, undermine the pit walls enough to cause a collapse.

The sump pit is the last line of defense against a flooded basement. If the pit liner itself develops a crack, water can bypass the pump intake and seep into the surrounding floor or worse, undermine the pit walls enough to cause a collapse. Catching and sealing a liner crack early is a straightforward repair that costs far less than a flooded basement cleanup.

How Sump Pit Liners Crack

Polyethylene plastic liners can crack from:

• Freeze-thaw cycles in areas where the pit extends near the frost line
• Soil settlement that shifts the liner out of position
• Impact from tools or the pump hitting the liner during service
• UV degradation in older, thinner liners

Concrete sump pits crack from hydrostatic pressure, shrinkage, and the same freeze-thaw forces that crack basement walls. Both types can be patched with the right material.

Tools and Materials

• Hydraulic cement (for concrete pits and large gaps)
• Plastic-compatible sealant or two-part epoxy (for polyethylene liners)
• Wire brush and angle grinder (for concrete surface prep)
• Shop vacuum
• Rubber gloves and eye protection
• Bright work light or headlamp
• Pump-out bucket or submersible utility pump
• Plastic sheeting

A reliable product for concrete sump pits is Hydraulic Cement by Quikrete, which sets in three to five minutes even against active water seepage.

Step 1 — Safety First

Turn off and unplug the sump pump. If your pump is hardwired, turn off the circuit breaker for the sump pump at the panel. Do not skip this step — water and electricity are a deadly combination.

Step 2 — Pump Out and Dry the Pit

Use a utility pump or a shop vacuum to remove standing water from the pit. If water is actively seeping in, bail as much as you can and work quickly. The pit does not need to be bone dry for hydraulic cement, but it must be free of standing water for epoxy sealers.

Step 3 — Locate All Cracks

Shine a bright light down into the pit and inspect all surfaces — bottom, sides, and the area around the pipe penetrations. Mark each crack with chalk or a marker so you do not miss one during repair. Probe each crack with a screwdriver to check depth and whether the liner is still solid on both sides.

Step 4a — Repairing a Concrete Pit

Widen hairline cracks slightly with a chisel or angle grinder equipped with a diamond wheel to create a keyway that gives the patch material more surface to grip. Brush the crack clean with a wire brush. Mix hydraulic cement to a putty consistency, shape it into a cone, and press it firmly into the crack while working against any active seepage. Hold it in place for three to five minutes until it sets, then feather the edges smooth.

After the hydraulic cement cures, apply a coat of Drylok Extreme Masonry Waterproofer over the entire pit interior for added protection.

Step 4b — Repairing a Plastic Liner

Clean the crack and the surrounding area with isopropyl alcohol to remove oil and mineral deposits. Apply a plastic-compatible two-part epoxy or a polyethylene patch tape rated for wet environments. Press firmly and hold for the manufacturer-specified bonding time. For larger cracks, cut a patch from a scrap piece of liner material and bond it over the crack with epoxy.

Step 5 — Inspect Pipe Penetrations

The discharge pipe and any drain tile inlets that pass through the liner wall are common seepage points. Check the sealant around each penetration. If it is cracked or missing, apply hydraulic cement around concrete pit penetrations or butyl tape around plastic liner penetrations and reseal.

Step 6 — Cure and Reinstall

Allow the repair to cure fully per the product instructions — typically 24 to 48 hours. Once cured, reinstall the pump, reconnect the discharge line, and restore power. Fill a bucket with water and pour it into the pit to verify the pump activates at the correct level and the repaired walls stay dry.

When to Replace the Liner

If the plastic liner is crushed, cracked along most of its circumference, or has shifted so that it no longer sits plumb, patching is a temporary measure. A full liner replacement — pulling the old liner, cleaning the pit, and dropping in a new basin — runs $150 to $400 in materials and is a full-day project that restores long-term reliability.