How do I waterproof or seal a basement foundation wall that leaks?

To keep a leaking basement foundation wall dry for good, the durable fix is interior drainage, not a coat of sealant. Our Forever Dry System runs full-perimeter interior drainage to a sump pump, with a 12-mil wall vapor barrier and a dehumidifier. Basement waterproofing costs $3,000 to $30,000. A paint-on sealer can slow a small damp spot, but it will not stop water pushing through under pressure. The water needs somewhere to go.

A wet foundation wall is one of the most common calls we get in New Hampshire. People reach for waterproof paint first because it is cheap and easy. But sealer sits on the inside face of the wall while the water comes from outside under pressure, so block it at the surface and it finds the next gap.

Why the wall is leaking

Water pools against your foundation because the soil around it is disturbed backfill, the looser dirt shoveled back after digging the hole for your house. It drains slower than packed natural ground and holds water. After a hard rain or spring melt, that wet soil leans on the wall and the water hunts for a way in. NH frost heave makes it worse: frozen ground expands and pushes inward all winter, opening cracks over the years. Every one becomes a door for water.

Why a sealer alone usually fails

Surface sealers and waterproof paints work against hydrostatic pressure, a fancy way of saying water shoving on the wall from behind. The paint holds for a while on a minor, occasional damp patch, but under real pressure it bubbles, flakes, and leaks again.

Plain version: if you have one small spot that sweats now and then, a sealer might buy you time and you do not need a full system yet. If water actually runs in after storms, sealer is money at the wrong end of the problem.

The fix that holds: interior drainage

For a wall that genuinely leaks, the route that lasts is our Forever Dry System. We run drainage around the inside perimeter of the floor, set a sump pump sized at half a horsepower per 120 feet of drain, hang a 12-mil vapor barrier on the wall, and add a dehumidifier. Instead of fighting the water, we give it a path to the sump and out. It is 100% guaranteed to be dry for life! That guarantee is transferable, with conditions.

We do not do exterior excavation to waterproof a wall. In our field experience, digging out the foundation and re-coating the outside fails in about two to three years. The dirt settles, the coating cracks, and you are back to square one with a bigger bill.

Worried about losing power in a storm? The backup sump is battery only, and a charged battery keeps pumping through a typical outage before it runs down.

When sealing the crack is the right call

If the leak is one narrow, stable crack and not water across the whole wall, you do not need the full system. We seal it with crack injection, epoxy or polyurethane pumped full depth, which costs $1,000 to $3,000 and carries a 10-year warranty. That is the smaller, cheaper fix, and we will tell you if it is all your wall needs.

What pushes us past injection is movement: a horizontal crack across a block wall, a wall bowing inward, or stair-step cracking. That is soil pressure or settlement, and sealing the leak will not fix the cause. For a bowing wall we use carbon-fiber straps at $850 each on a 25-year warranty, or a power brace at $1,300 per brace. For settlement, helical piers at $2,700 per pier for the first three, then $2,200 per pier after that on a 25-year engineered warranty. See our structural and foundation repair and foundation repair pages.

What it comes down to

Three roads. Seal one stable crack with injection. Run interior drainage if water comes in across the wall or at the floor wall joint. Look at stabilization or piers only if the wall is moving. We come out, check for movement, and tell you which your basement needs. The inspection and estimate are free, and you get a quote within 24 hours.

On money, foundation work scares people because they picture the worst number, but a small crack is usually the cheapest fix on the menu. To spread a bigger job out, we offer financing through Hearth, subject to approval, and 603 makes nothing on it. For what to ask any contractor, see the 603 guarantee.

For neutral background on foundation water and soil, the DOE Building America program (basc.pnnl.gov) is a solid read.

Closing

Call us at 603-610-1770 or book your free inspection. We will look at the wall, check for movement, and give it to you plain.

Related questions

Does waterproof paint actually work on a basement wall? On a minor, occasional damp spot, it can help for a while. Against real water pressure it bubbles and leaks again, because the water is pushing from outside. For a wall that truly leaks, interior drainage is the fix, our Forever Dry System at $3,000 to $30,000.

Should I waterproof my basement wall from the inside or outside? Inside. We do not dig out the foundation to coat the outside, because in our field experience that fails in about two to three years. Interior drainage to a sump is the route that lasts.

Can I just seal the crack instead of doing a whole system? If it is one narrow, stable crack, yes. Crack injection runs $1,000 to $3,000 with a 10-year warranty. If water comes in across the wall, the crack is only a symptom and you need drainage.

Do you waterproof crawl spaces the same way? No. A damp crawl space gets crawlspace encapsulation, not the Forever Dry System, which costs $3,000 to $25,000.