Rising damp is the wicking of water through the footing, into the concrete wall, and its evaporation inside the building. Rising damp increases the moisture load which leads to dampness and mold.
Rising damp does not produce pools of water (as with liquid water entering a concrete wall), but rather a chronic musty smell, growing insidiously stronger when the footing is exposed to more moisture.
The worst case of rising damp occurs when water ponding occurs at the footing level. This occurs over impervious soils where the excavation is inadequately sloped, the drain tiles are not located below the bottom of the footing, and no sub-footing drainage layer was installed.
Even without water ponding, rising damp occurs when unprotected footings are exposed to damp ground. 'Hygroscopic' concrete wicks ground moisture up into the foundation concrete which is then evaporated inside the building. Fastfoot® prevents this wicking from occuring, providing a drier and healthier indoor environment.
Rising damp is prevented by isolating the concrete footing from ground moisture. While it is normal in the industry to protect the foundation wall from ground moisture with a damp proof membrane, no effort is made to protect the footing concrete. However most moisture is located at the bottom of the excavation, where the footings are located.
With impervious subsoils it is important to prevent water ponding from occuring at the bottom of the excavation. Four preventative steps should be taken: first, place a slight grade on the excavation so that ponding cannot occur; second, place a non-wicking drainage layer under the footing to enable any ground water to exit to the perimeter drain system; third, locate the bottom of the drainpipe below the bottom of the footing concrete; and fourth, use Fastfoot® to protect the concrete footing from ground moisture on the bottom, sides and top of the footing.
Both water ponding and rising damp is evident in this crawlspace in Surrey BC. Note the effervescence on the stem walls from rising damp travelling up through the footing, into the stem wall and evaporating inside the crawl space.
Poor drainage, an improperly sloped excavation, and no sub-footing drainage layer caused water ponding. No damp proof membrane around the footing resulted in rising damp.
Humidity levels are 100%, resulting in mold and mildew and a very unhealthy envirnoment for the homeowner.
In the image to the right, water ponding is occurring because of inadequate slope in the excavation, no drainage layer under the footing, and the drain tile located above the bottom of the footing.
The photo to the right shows an excavation where there is inadequate slope on the excavation, no drainage layer, and the drain pipes are positioned above the bottom of the footing. As there is no damp proof protection around the footing, there is a high probability of rising damp occuring for the life of the buildings.
CMHC (Canada Mortgage and Housing Corporation, Canada's National Housing Agency), conducted a survey of 405 houses in the Ottawa region of Ontario, Canada. The objective of the survey was "to determine whether typical 'finished' basements are contributing to poor indoor air quality as a result of mold growth in the finishing materials". About half of the 405 houses "had signs of moisture in the basement". The study then selected 22 for further investigation. Molds were found in 18 of the 22 houses, or 82%. Mold samples were taken from 16 of the 18 houses.
In 100% of those houses, "molds with properties that are harmful to humans were found."