Mold, Mildew concrete basement wall and floor

Published on April 6th, 2016 | by Henri


Basement walls moist and moldy

Q.  I had a French drain installed last year which keeps the floor dry, but the cellar walls are moist, and there is mold on them. I would like to dig on one side of my house and put down some barrier against the wall, and then put the dirt back and regrade and put in a sidewalk.

Please advise me what to put against the wall (tar paper, tar, etc.) and should I put rocks with the dirt? Should I dig down to the bottom of the foundation?

A.    Before you undertake such a monumental job, check the grade and any appendages next to the foundation of your house. It is possible that the walls are kept moist because the ground is too flat or slopes towards the house; a concrete patio, driveway or sidewalk also tilts toward the foundation; or a downspout discharges water that pools against the foundation instead of draining away from it.
If there are such deficiencies, and you take care of them, you may not need to tear up your yard and dig down to the footings.

The mold can be removed by scrubbing the walls with a stiff bristle brush, using a solution of equal parts fresh Clorox bleach and water. Wear rubber gloves and eye protection against splashing. Do not rinse; let the solution do its work.

You haven’t said what is your foundation built of: poured concrete or blocks. Also important to know is the composition of the soil backfill and whether your lot is flat or sloping away.

If all else fails and you decide to proceed with the digging, instead of using tar paper, place 6-mil black plastic against the wall. It works much better than tar paper, and you won’t need to clean the walls of all dirt.

  • If the soil is heavy (clay or silt), it will be best to backfill as follows:
  • Pin a 4-foot wide band of geotextile fabric against the outer bank of the excavation from the bottom up.
  • If the lot slopes and you can daylight a drainpipe, lay a couple inches of egg-size stones on the bottom of the trench, lay a 4-inch perforated pipe on the stone bed and connect it to a solid pipe to daylight.
  • Add a foot or more of the same stones over the perforated pipe. Fold the fabric over the stone bed and up the house wall.
  • Continue the backfilling with coarse sand or bankrun gravel to within a foot of the final grade.
  • Finish backfilling with native soil and slope it gently away from the foundation.
  • Backfill the solid pipe with native soil, and plant grass.

However, if your lot is flat and you can’t drain to daylight, just backfill as described above but without using the drainpipes.

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