How to Keep Basements Dry: Use Membrane Capillary Breaks Above Footings
It’s important to separate a foundation wall from damp soil so that migrating moisture does not reach the structure’s framing and/or interior. To preempt the costly problems from ground moisture reaching foundations, contractors routinely employ these solutions:
- Asphalt dampproofing on the exterior surface of foundation walls
- A layer of polyethylene and crushed stone under the basement slab
- The use of closed-cell foam between the top of wall and mudsill
But, none of these moisture-resistive steps address the problem of moisture migrating from the footings into the foundation wall. Only proper capillary breaks on footings can stop this undesirable movement of water.
Without capillary breaks between footings and foundation walls, unhealthy conditions can develop. Capillarity can also lead to premature deterioration of materials sensitive to moisture and mold growth.
Just as a dry sponge soaks up water, concrete walls have the capacity to wick moisture up from the footings. As Dr. Joe Lstiburek from Building Science Consulting states, the theoretical limit of capillary rise in concrete is 10 Kilometers! So-called “capillary rise” is often a serious challenge in structures with concrete footings and concrete foundation walls. And according to Martin Holladay, capillary rise can contribute up to 15 gallons of water a day to a home’s interior moisture load!
GreenBuildingAdvisor explains that the phenomenon occurs when the forces of adhesion are stronger than the forces of cohesion. When the attraction between water molecules, and molecules in the wall exceeds the attraction of water molecules to one another, capillary rise occurs. This capillary action causes moisture in damp soil to migrate first to the footings and then up into the foundation walls.
In many instances, moisture can travel several feet before the forces of cohesion and adhesion are in equilibrium. In a typical residence, capillary rise may add numerous gallons of water to the moisture load inside the home. The contrast in capillarity from one material to another can even be striking. Water may rise as much as 20 feet in certain clay soils, but only inches in crushed stone.
To avoid the adverse consequences of such moisture migration, a capillary break is required between the footing and the wall. There are a variety of products that have been deployed as capillary breaks:
- Membranes like DELTA®-FOOTING BARRIER
- Latex masonry paint and asphaltic dampproofing
- Polyethylene sheeting
Architects, designers and contractors have two primary options when it comes to capillary breaks between basement walls and concrete footings: membranes and fluid-applied waterproofing.
Contractors should follow manufacturer recommendations and wait before using fluid-applied products on new concrete footings. Some products require up to a 4-week wait as the concrete must fully cure before application. The concern is that such products will be prematurely applied, potentially compromising effectiveness through improper bonding and even cracking. Of course, scheduling pressures are all too common. Architects that stipulate the use of a membrane as a capillary break can avoid this problem.
Accommodating Rebar or Keyways
To facilitate the use of a membrane as a capillary break, a concrete wall should be keyed to a concrete footing through the use of a keyway. Vertical rebar can be employed for increased structural integrity when necessary and is typically required in earthquake zones. When vertical rebar is present, contractors often opt for fluid-applied products. However, membranes still remain a viable option.
Although claims have been made that the use of an appropriate concrete additive will reduce capillary rise, many manufacturers of such a product are unwilling to make such a broad promise. Choosing a different solution, some builders choose polyethylene sheeting under footings, however bonding issues can make it less reliable.
A Solid Membrane Solution
DELTA®-FOOTING BARRIER is a water-resistive capillary break. It is extremely pliable, adheres well to wet concrete footings and can be applied by a single person. When pouring footings, the membrane is simply laid into the fresh concrete with a hand trowel. The fuzzy texture on the backside of the membrane helps to form a more connected interface between the surfaces once the concrete has cured. Forming the keyway is simple enough for one person to manage using a common two-by-four piece of lumber.
Vertical rebar is easily accommodated by DELTA®-FOOTING BARRIER with an X-cut into the membrane through which the metal is inserted for placement in the wet concrete. Forms for the foundation walls are then placed and the concrete is poured normally. This straightforward application of the membrane not only creates an elegant, simple solution to prevent capillary rise and basement dampness but has both performance and application advantages over fluid-applied waterproofing and other barrier methods.
Watch our latest webinar from Dr. Joe Lstiburek to see how to provide superior protection for below-grade living spaces. Visit our site to see the full-line of DELTA® products designed to keep your basement dry.
Dörken delivers innovative, high-performance air and moisture barriers for commercial and residential construction. It is sold under the DELTA® brand name. A North American manufacturer based out of Beamsville, Ontario, Dörken Systems, Inc. is a subsidiary of Ewald Dörken AG, a leading European developer and manufacturer of waterproofing and drainage products sold worldwide. Dörken is known for delivering premium products while providing educational programs and full technical support. For more information, call 1-888-433-5824 or visit www.dorken.com.