TV47 Earthwork

Moisture seeping into the basement around the perimeter of building because of inadequate drainage has caused damp and mold growth in basement. Mold growth is evident at foot level in e.g. the mechanical room, notably at the foundation corners (which also coincide with gutter downspout locations).

Exterior remediation

• Excavate soil around exterior perimeter of foundation. Depth of trench: ideally to the level of the foundation footing, if you can find the footing. If you cannot reach the footing, excavate at least 6-12 inches/15-30 cm below level of basement slab. Width of trench: enough to allow a person to work in side; shore the trench as needed for safety based on soil conditions.
• If foundation is very uneven (e.g. large holes from irregularly sized stones, mortar gone, etc.) address the problem by either pouring a few inches of concrete around the perimeter of the foundation wall or parging the walls with mortar. Concrete is a better solution but is more involved (requires formwork).
• Coat foundation wall with tar/bituminous material for hydroinsulation, then cover with a plastic moisture barrier (e.g. polyethlyne sheeting) while tar is still tacky. Ideally over footings include the tar and plastic sheeting over footings.
• Place a few inches (10 cm) of gravel in the bottom of the trench.
• Place landscape fabric on top of gravel layer; allow enough fabric to subsequently cover drainage pipe and 6 inches (15 cm) of gravel.
• Place perforated drain pipe on top of gravel, pitched 1/4 inch per foot (1:50 slope) to allow water to flow away from house.
• Connect perforated drain pipes around perimeter of basement to solid PVC drainage pipes (minimum 4 inch/10 cm diameter) that drain to daylight.
• Cover perforated drain pipe with cca 6 inches (15 cm) gravel around entire perimeter of house, then cover gravel with landscape fabric to keep dirt/sediment from entering drain pipes.
• Backfill trench, ideally with pure gravel/stone to relieve hydrostatic pressure on basement wall; if not with mixed stone and dirt.

Correct gutter drainage: all gutters should drain via a solid PVC drain pipe (4-inch (10-cm) diameter minimum) to daylight.

Interior remediation

• Scrape interior basement wall surfaces clean mechanically with wire brush.
• Ensure surfaces are dry, using ventilation and dehumidifiers as necessary.
• Treat basement walls with fungicide.
• Build up low areas with mortar (use a metal wire mesh to support mortar as needed, like for stucco).
• Cover basement walls with whitewash.