Foundation dampproofing is a coating, typically asphalt-based, applied to the exterior of a foundation wall to resist moisture absorption from surrounding soil, without being rated to block standing water under pressure. It’s a baseline level of protection, often code-required as a minimum even where full waterproofing isn’t necessary.
Because dampproofing is relatively inexpensive to apply during original construction, it’s commonly used as a matter of course on foundations that aren’t expected to face significant water pressure.
What Does Foundation Dampproofing Involve?
- An asphalt-based or similar coating applied to the exterior wall
- Application after the foundation cures and before backfilling
- Coverage of the wall from footing to grade level
- Pairing with proper site grading and drainage
Why Is Foundation Dampproofing Important?
Even on sites without a high water table, soil naturally holds moisture that can wick into porous concrete over time, and dampproofing blocks that gradual absorption from becoming a persistent moisture problem inside. It’s important to recognize dampproofing’s limits, though, since it isn’t designed to resist actual standing water pressure, which is exactly the situation waterproofing is built to handle instead.
A foundation that was only dampproofed but later experiences changed drainage conditions nearby, such as a new downspout or altered grading sending more water toward the wall, may need to be upgraded to full waterproofing to keep the basement dry. Building codes in many jurisdictions specify dampproofing as the minimum acceptable protection for basement walls, treating full waterproofing as an upgrade required only under specific site conditions like a documented high water table. Applying dampproofing correctly also depends on timing, since the coating needs to cure fully before backfilling begins or it risks being damaged before it can do its job.
Foundation Dampproofing vs. Foundation Waterproofing
Dampproofing resists moisture absorption under normal soil conditions; waterproofing resists actual water pressure. Basements with a high water table or poor drainage need waterproofing, while dampproofing may be adequate on well-drained sites with minimal water exposure.