Exterior waterproofing: stopping water before it reaches the wall
This is the approach that keeps the wall itself dry. The soil is dug away down to the footing, the outside of the foundation is coated, and a new drain is laid alongside. It is also the one that tears up the yard.
What goes on outside the wall
Section through a foundation wall with the outside excavated.
- Trench Soil is dug away from the wall all the way down to the footing.
- Membrane The cleaned wall gets a waterproof coating or sheet from the footing up to ground level.
- Drainage board A dimpled sheet protects the membrane and gives water a clear path straight down.
- Footing drain New perforated pipe in washed stone carries the water to a sump basin or an outlet.
- Backfill The trench is refilled in layers, ideally with material that drains more easily than what came out.
- Grade The finished surface slopes away from the house so rain runs off.
When digging outside makes sense
- The basement is finished and you would sooner lose a flower bed than a wall of drywall.
- The wall leaks along its height, not only at the floor, or its mortar and coating are crumbling.
- Only one side is wet, usually the side the ground slopes down toward.
- The wall is being dug up anyway for a new window, a sewer repair or an addition.
It makes less sense where a driveway, a porch, a deck or the neighbor's lot sits tight against the wall, because the machine cannot get in and everything in the way has to be rebuilt. It also does little for water that rises under the floor unless the new drain has somewhere to empty.
What it does to the yard
Expect a trench as deep as the basement along every wall being treated, and a pile of soil on the lawn beside it. Shrubs, walks, steps, air conditioner pads and anything else within a few feet of the wall come out first.
Refilled soil settles for a season or two. The slope away from the house that looked right on the last day can turn into a dip by the next spring, so ask whether the company returns to top it up.
Buried gas, electric and communication lines have to be marked before a machine arrives. The guide to flood maps and calling 811 explains the notice Diggers Hotline needs.
Ask before the excavator comes
- How far down and along which walls will you dig?
- What goes on the wall: a sprayed coating, a sheet, or both?
- Where does the new drain empty: a sump basin indoors or an outlet in the yard?
- Who contacts Diggers Hotline, and who pays if a sprinkler pipe or other private line is cut?
- What are you refilling the trench with?
- Who replaces the walk, steps, plants or deck you take out?
Inside or outside?
An interior drain manages water once it is through the wall and costs you a strip of floor. Exterior work stops it at the wall and costs you the yard. Some houses get both: an outside membrane on the one bad wall and an inside drain for the rest. A company that only ever proposes one of the two is selling what it has.
Exterior waterproofing questions
Is damp-proofing the same as waterproofing?
No. The thin black coating sprayed on many foundations when they are built is damp-proofing. It slows moisture from the soil but does not hold back water under pressure. A waterproofing membrane is thicker and made to stretch across small cracks. Ask which of the two is in the quote.
Will I still need a sump pump?
If the new footing drain cannot run downhill to an outlet on your own lot, it has to end in a sump basin with a pump. On a flat lot that is usually how it ends up.
Can this be done in winter?
Frozen ground is harder to dig and harder to compact when it goes back. Ask the company when it schedules exterior jobs and what it does if the weather turns.
Talk it through with a local company
Call and describe what the water is doing. You will speak with an independent local waterproofing company about coming out to look at your house.
For homeowners: basements, crawl spaces, sump pumps and drainage.
Call (262) 257-3901Racine Basement Waterproofing Help is a referral service, not a contractor. Calls may be recorded. Referral disclosure.