How to Solve Foundation Wall Moisture Problems?


A very common problem in basement spaces is the presence of moisture on the perimeter walls. This occurs due to a number of conditions that can allow water to penetrate the walls or merely condense on the inner surface of the foundation wall.

Let’s look at the condensation issue, it is the most common and normally the easiest to handle.

Condensation occurs when the air in the basement space is full of water. Humidity is the measure of moisture in the air. On a humid day you are more likely to perspire due to the fact that the air is full of moisture. In the basement when this air comes in contact with a cooler surface, such as the concrete walls or floor, moisture will condense out of the air. Cool air has less moisture carrying capacity than warmer air, so the coolness of the concrete, whether the walls or the floor, causes the layer of air immediately adjacent to the surface to cool down and the moisture to drop out of the air.

This condition can be resolved in a number of ways.

  • Insulation on the exterior walls or floors; if the walls are covered with an insulating material, foam insulation board, fiberglass batt insulation and then covered with sheetrock or paneling, the condensation will be reduced. If this is the solution you choose, don’t forget a vapor barrier, and the rule to follow, vapor barrier always on the warm side of the wall system. You do not want to trap the moisture in the wall; you want to prevent it from ever getting into the wall system. If the floors are condensing, then the application of sleepers is recommended. These are strips of wood, aluminum, or even plastic standoff bases that raise the application of a flooring material above the concrete surface. Insulation can be installed between the sleepers to further decrease the temperature differential, between the interior air, and the surface of the concrete.
  • De-humidification systems; the purchase of free standing de-humidification units will reduce the amount of moisture in the air within the basement. If the moisture content is reduced, the condensation will be reduces or eliminated. There are also de-humidification systems that can be installed with or without the ability to heat and cool the space. These are more reliable and certainly will take more moisture out of the air throughout the basement area, than the smaller, mobile units. The piping of either system, whether by flexible hose or hard piping will eliminate the need to continually empty the water containers within the units as they work to take water out of the air.
  • Added ventilation; there are systems that use the exchange of air and additional ventilation to reduce the amount of water in the ambient air and therefore reduce the condensation occurring in the basement. These systems are quite successful and will reduce the amount of moisture in the basement space.

If water is actually penetrating the exterior foundation walls and entering the basement space, this condition is more difficult to specifically identify and correct.

There are several ways to approach this issue;

  • There might be actual cracks or failures visible on the interior surface of the concrete foundation walls. These failures will be moist and even dripping with water. There are number of products developed to apply directly on, and into these failures. In some applications the manufacturer recommends a routing out of the crack or failure. This means that the failure should be either ground out, chopped out, or chiseled out in an attempt to form a V groove. This V groove is then thoroughly dried out and the sealant applied. Again, there are several types of sealant and products that have been developed to seal these failures in the foundation wall. Some of the sealants actually expand to ensure water tightness; others incorporate waterproofing agents that seal the water out of the interior of the space.

Unfortunately, this type of correction and attempt to stop the water from penetrating the exterior wall is usually hit or miss. If the walls have cracked and those cracks are sealed, there is a good chance that additional cracks could develop. If the sealant works, there is a time limit to its holding capacity and the leak may re-occur.

  • Another solution to water penetrating the exterior foundation walls, is a system that actually allows the water to penetrate and drip or flow, dependent upon the quantity, down the wall to a drain located at the base of the wall. This drain is either exposed or hidden within the finished wall space of the perimeter wall assembly. This techniques of solving the water conditions within a basement space, uses the application of a vapor barrier again, on the warm side, of the wall, stopping the moisture from getting into the space.

This solution is a relatively costly solution, due to the fact that the drain is normally installed around the entire perimeter of the basement, and a sump and pump is needed to drain and pump the moisture out of the basement to the exterior or a sanitary drain.

  • It is my opinion that the best method for stopping water from penetrating the foundation walls is to stop the water! This may seem obvious, but unfortunately this is usually a difficult endeavor. If the water could have been stopped at the time of construction, it would appear, that this would have occurred. The following steps should be taken;
  • The exterior of the foundation wall needs to be excavated where the water is penetrating the wall. This excavation should be overly large around the crack or wall failure. One of the difficult issues with water is that it travels, this means that the water that is penetrating the wall may be originating several feet away. Therefore the excavation should be generous.
  • The foundation wall should be power washed thoroughly and cleaned of all dirt.
  • The foundation wall must be allowed to dry off, after the power washing, to allow the membrane waterproofing to adhere.
  • The entire foundation wall should be covered with a thick layer of membrane waterproofing. There are several products that will adhere to the wall and are impenetrable.
  • Once the waterproofing is placed on the wall, a layer of foam board should be installed. This foam board will provide insulation as well as protection for the waterproof membrane.
  • A layer of drainage board should be adhered to the outer surface of the foam board to provide a path for the water to travel down to the footing drain, which is to be installed.
  • Over the drainage board should be applied a protection layer of felt, additional foam or specific protection board to eliminate damage to the drainage layer.
  • This entire system should be drained down to a full perimeter footing drain that either exits to grade or empties into a drywell, or sump with a pump.
  • The idea of this method of stopping the water from penetrating the foundation wall is to stop it, prior to it ever getting to the exterior surface of the wall.

If this entire procedure is followed, I guarantee that the water will be stopped from penetrating the foundation at these specific areas. As can be predicted, this procedure will cost money and will take time and effort.

Once the entire system is applied, the backfilling of the wall should occur with a free draining material that will allow the water to percolate down to the footing drains along the wall itself, further back from the wall; less permeable material can be used, in an attempt to retard the traveling of the water to the wall itself. The slope of the exterior grade should be maintained away from the exterior of the structure to a drainage swale that will lead the surface water away.

I stress, that the elimination of water penetrating the foundation walls, should be part of the normal construction activity and procedures. There is no reason that water should be penetrating a foundation wall. There are methods and techniques that can be done during construction to ensure that the foundation is watertight. It is so much easier and cost effective to solve the issues during construction, than after the structure has been built.

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