Membranes and footing drains
Exterior waterproofing: stopping water at the outside of the wall
Exterior waterproofing is the only method that keeps the wall itself dry. The soil is dug away, the outside face is coated and a new drain is laid at the bottom. It is also the method that tears up the yard, so it tends to be chosen for one troublesome wall and not the full perimeter.
Call (205) 555-0115When the outside route makes sense
Three situations favor it. The basement is finished and you would sooner lose a flower bed than a room. The wall is block or brick and is being damaged by staying wet, with mortar washing out or white crust building up. Or the trouble is confined to one stretch that a digger can reach.
It makes less sense where a driveway, a porch slab, a deck or a neighbor's fence sits tight against the wall, or where the wall is deep. Then the digging costs more than the waterproofing.
Drawing
Outside the wall: what goes where
- Excavation. A trench is opened along the wall, all the way down to the footing, wide enough for someone to stand in.
- Membrane. The cleaned wall gets a rubbery coating or sheet, often with a dimpled board over it so water falls freely.
- Footing drain. Perforated pipe wrapped in fabric lies in washed gravel beside the footing and carries water off.
- Inside liner. Part of an interior system, shown for comparison.
- Inside drain. Also interior. It collects water after it has come through.
- Sump basin. Either system may need one if there is no downhill outlet.
Where the collected water goes
A footing drain is only as good as its outlet. On a sloping lot the pipe can often continue downhill and open onto your own ground, which needs no pump and no electricity. Ask to be shown where that outlet will be and how it is protected from being buried or crushed.
On a flat lot the pipe goes to a sump basin, indoors or in a pit outside, and a pump lifts the water out. Then the pump is part of the system and needs the same attention as any other.
What happens to your yard
Everything growing against that wall comes out. So do steps, air conditioning units, meters and anything else in the way, or the trench is hand-dug around them. Soil is piled on the lawn, usually on sheeting, and a small excavator will leave tracks.
Before any of that, buried utilities have to be marked. In Alabama whoever is doing the digging must notify Alabama 811 between two and ten working days ahead, not counting the day of the request, and must dig by hand, or by other careful means, within 18 inches of a marked line. The company should make that request itself. Alabama 811 explains the steps. Utility companies mark their own lines. Point out anything you had buried privately, such as sprinkler pipe or lighting cable.
Backfilling matters too. The trench should be refilled in layers and the surface left sloping away from the house, a little high, because it will settle.
Questions about an exterior job
- How deep is the footing here, and are you digging to it along the whole length?
- What product goes on the wall, and what protects it during backfill?
- Where does the new drain discharge?
- Who contacts 811, and who deals with the air conditioner, gas meter and steps?
- What is the yard left like: rough grade, topsoil, seed, sod?
- If cracks are found once the wall is exposed, what happens next and who decides?
Cracks found once the wall is bare
Digging shows the wall as nobody has seen it since the house was built. Hairline cracks get sealed under the membrane as a matter of course. A wall that is bowed inward, or a crack with one side stepped out from the other, is a structural question. The company should stop, show you, and suggest an engineer or foundation specialist before covering it up again.
Exterior waterproofing questions
Is outside always better than inside?
It is more complete, since the wall stays dry. It is not always the sensible choice. Where access is poor, an interior drain gives a dry room for far less upheaval.
Can this be done on a crawl space wall?
Yes. Crawl space walls are shallower, so the trench is smaller. It is sometimes done on the uphill side of a house before the space is encapsulated.
What time of year is it done?
Whenever the ground can be dug and the wall can dry enough for the coating to stick. A run of dry days matters more than the season.
Do I need to tell my neighbor?
If the trench runs close to the boundary, yes, out of courtesy and because machinery may need room. The company should stay on your property unless your neighbor agrees otherwise.