Foundations
and Slabs
Many older homes have foundations that have cracked or settled. Check the foundation
wall for deterioration that could allow water to enter the basement. Check both foundation walls and piers for settling. Windows
or door frames out of square or loosened interior wall finish suggest that the foundation has settled. Correct minor
settling by jacking and re-leveling beams and floor joists. Individual piers can be replaced. But if the pier has stopped
settling, jack the supported girder or joist and add a block to the top of the pier.
Most concrete
foundation walls develop minor hairline cracks that have no effect on the structure. However, open cracks may indicate a failure
of the foundation that’s getting progressively worse. To find out if a crack is active or dormant, scratch a line at
the end of the crack and wedge a nail tightly into the crack. If the crack grows beyond the scratch mark or if the nail can
be removed easily several months later, the crack is probably active.
If a crack is dormant, it
can be repaired by routing and sealing. Enlarge the crack with a concrete saw or by chipping with hand tools. The crack should
be routed 1-1/4" or more in width and about the same depth. Rinse the joint clean and let it dry. Then apply a joint
sealer such as an epoxy-cement compound in accord with the manufacturer's instructions.
Active
cracks require an elastic sealant. Again, follow the manufacturer’s instructions. Good-quality concrete sealant will
remain pliable for many years. The minimum routing depth and width for these sealants is 3/4". The elastic material will
deform but maintain a tight seal as the crack moves. You could also apply a strip sealant over the crack. But these protrude
from the surface and make a poor choice if the wall is visible from the building exterior.
Repair
loose mortar by brushing thoroughly to remove dust and loose particles. Before applying new mortar, dampen the clean surface
so that it won’t absorb water during repair. You can buy premixed mortar with the consistency of putty. Apply mortar
over the cavity as if you were filling a void with painter’s caulk. For a good bond, force mortar into the crack. Then
smooth the surface with a trowel. Cover with a vapor barrier for a few days to keep the mortar from drying too fast.
Damp or leaky basement walls are usually caused by clogged drain tile, clogged or broken downspouts, cracks in walls,
or by water that puddles against the foundation. Look for downspouts that empty against the foundation wall or surface drainage
channeling by the foundation. For a dry basement, keep water away from the foundation by proper grading.
Pre-construction ChecklistPre-construction Checklist
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A high water table is a more serious problem. A basement will never be completely dry if the water table extends
above the basement floor. Heavy foundation waterproofing or footing drains may help, but they’re unlikely to do more
than minimize the problem.
