A.Henri de Marne
responds: The system the specialty contractor describes is
commonly used by residential water-proofers. The injected
coating, which is probably bentonite, is generally effective
for only a short time, and is probably not worth the added
expense. But the interior drain will remove the bulk of the
water, and will last a long time, if done properly.
I have used an interior perimeter drain connected to a sump
pump a number of times. It is often the best choice, depending
on the house site. In general, I choose an interior drain
when:
- Landscaping is extensive, long established, and
valuable, and the risk from moving it is too great.
- There is not enough space to store the excavated dirt,
wheel in stones and coarse backfill, or safely excavate a
sufficiently wide trench.
- There is no access to the backyard or the sides of the
house.
If you opt to do the work on the inside, consider using
channel drain — a PVC or fiberglass enclosed gutter with
holes in the top, such as Microchannel (NDS, 3001 Mission Oaks
Blvd., Camarillo, CA 93011; 805/389-6700). It’s best to
embed the channel in the slab, but you can install it over the
slab with satisfactory results. Drill holes in the back of
channel drain and embed the channel in a thick bead of caulk,
as shown in Illustration A, below. Etch the slab with muriatic
acid before applying the caulk. I use Sikaflex-1A sealant (Sika
Chemical Corp., 201 Polito Ave., Lyndhurst, NJ 07071;
201/933-8800), which sticks well, even under the harshest
conditions.
An interior perimeter drain can be
fashioned from PVC channel drain (left). First, etch the slab
with muriatic acid, then caulk the drain in with Sikaflex-1A.
An exterior drain (right) works as well, but is difficult to
retrofit if existing landscaping limits access.
As for outside options, there are essentially two
approaches. The most expensive way is to install a system such
as Enkadrain (Akzo Industrial Systems Co., P.O. Box 7249,
Asheville, NC 28802; 704/665-5050). Or you can install
foundation-grade poly and 1-inch rigid polystyrene insulation
against the foundation. In both cases, you have to lay a
foundation drain at the base of the footing in a gravel bed,
covered by a geotextile fabric, and then backfilled with a
coarse, well-draining soil to within a foot of the final grade
(Illustration B, above). Finally, top this backfill with native
soil as described below.
Having dealt with literally hundreds of foundation water
problems in nearly 40 years in the construction business, my
first recommendation is to correct any grade or "appendage"
(porch, stoop, sidewalk) problems. In my experience, surface
water accounts for 99% of wet basement problems.
To correct surface water problems, start by checking the
ground near the foundation for low spots (including holes dug
by dogs beneath the shrubbery), negative grade (sloping towards
the house instead of away from it), and rotting tree stumps
below grade. Inspect stoops, porches and sidewalks for cracks
or settlement (including hollow spaces beneath them). And look
for the absence of splash blocks or clogged and disconnected
gutters and drain pipes. All grades, including the grade under
open porches, stoops, and decks, should slope gradually (about
2 inches per foot) away from the foundation. Walks, driveways,
concrete steps and porches, and patios should be repaired to
slope away from the house at a pitch of about 1/8 inch per
foot. Fill depressions in the earth with loam — not
coarse material — and plant grass. Avoid flower beds,
shrubs, and mulched or graveled areas within a few feet of the
foundation.
The other 1% of problems are caused by underground springs,
hillside drainage, ledge, or a seasonably high water table, for
which the perimeter drain — inside or out — is the
only solution.
Henri de Marne, a former remodeling contractor and custom
builder, is now a home inspector and building consultant in
Waitsfield, Vt.