Thirty years ago most residential foundations were “waterproofed” with a solvent-based asphaltic product that was either sprayed on or hand applied. Sometimes installers added glass fibers to help the material stay together and to prevent cracking over time. But these materials didn't actually waterproof foundations, they dampproofed them, and are seldom used today. Asphalt, however, is still used in the manufacture of several different products used to waterproof foundations.
The terms dampproofing and waterproofing are sometimes used interchangeably but they don't mean the same thing. That asphaltic products of 30 years ago dampproofed walls because they only prevented the transmission of water vapor into the concrete. Waterproofing materials prevent the transmission of both liquid water and water vapor. Waterproofing materials are the product of choice today.
Types Of Waterproofing Materials
There are surprisingly few true waterproofing products available today. They are either spray-applied or are sheet goods that are attached mechanically or with adhesive. The basic materials include:
Solvent-based asphaltic emulsion. This can be sprayed or applied with hand trowels. Typically it is heated to make a sprayable liquid. Sometimes it is mixed with glass fibers to provide resistance to cracking and shrinkage. At one time the product of choice, this material is seldom used today.
Rubberized asphalt. Today this is the most commonly used material, marketed either as a sprayable material or as “peel and stick” sheet goods (the adhesive on the sheet adheres it to the foundation wall). There is usually a thin film of polyethylene or polyvinyl chloride (PVC) on the exposed side for easy handling. Both the sprayable and the sheet versions are sensitive to ultraviolet light so it must be covered and protected when it is exposed to sunlight. The sprayable version is predominately water-based, making it safer to work with but also susceptible to freeze damage before it cures. This material is installed usually within a couple days after form removal. The thickness of the dried membrane is typically 40 mils.
Rubber. This is a sprayed material made from a synthetic polymer mixed with a solvent. It is sensitive to UV radiation and can be installed as soon as three days after a foundation wall is cast. Because it is a solvent-based product, it can be applied at temperatures as low as 17° F. Installers generally spray 60 to 80 mils of material to finish with a 40-mil dry cover.
Polyethylene. Polyethylene is used in the manufacture of sheet membrane systems. Manufacturer Cosella-Dörken, Beamsville, Ontario, Canada, makes their product as a three-layer sheet. The two outside layers are high-density virgin polyethylene while the middle layer is recycled polyethylene to create a 24-mil-thick sheet—the recycled content allows them to market it as a sustainable or “green” product. Polyethylene also is sensitive to UV radiation, so there are added components to offer protection during construction.
Bentonite. Bentonite clay is a mined material that becomes a thick gel and expands when it gets wet, preventing the movement of water. It doesn't limit the movement of water vapor however. The clay is usually sandwiched between two layers of cloth or geotextile. There is an extensive amount of this product used for foundation wall waterproofing in the United States, especially for commercial construction.
Protection components. There are three common conditions that require one to cover waterproofing membranes: to protect them from damage from backfill, to insulate basements in order to conserve energy, and to provide water drainage away from the membrane. In northern freeze/thaw climates, most local codes now require foundations to be insulated either on the inside or the outside of foundation walls. For economic reasons the insulation is usually placed between the backfill and the membrane. Local codes also specify the R-value or a heating value requirement. For most applications, 1 or 2 inches of expanded or extruded polystyrene or fiberglass insulation boards meet the requirements.
The Systems Approach
Soil with high water content produces significant hydrostatic pressures against foundation walls, increasing the risk of leakage—water under pressure can make its way through the smallest pinholes. A “belt-and-suspenders” approach is therefore advisable: provide both a waterproof membrane and drainage next to the membrane, allowing water to freely move to the perimeter drain located alongside the footings. This eliminates water pressure against the membrane.
Building homes tighter in order to conserve on energy increases the problems of mold and mildew growth because relative humidity increases inside the building envelope. Thus a complete system to manage water becomes more important. The basic elements of a good system include:
- Drain pipes alongside the footing. There should be a drain on the inside and outside of the footing. If these drains can't run water away from a building by gravity, both lines should be routed to a sump pump. Install open-graded stone or gravel wrapped in geotextile cloth around the drainage pipes so that water can always move quickly to the drain. An intriguing product that replaces the drain pipes and also serves as the form for the footing is Form-a-Drain by Certain Teed. Also important is a backup system for sump pumps in case the electricity goes out.
- Waterproofing (not dampproofing) membranes against the outside of the foundation wall. Most membranes are affected by UV radiation, so membrane above ground must be protected from sunlight.
- Drainage products placed alongside the membrane against the exterior face of the wall to relieve hydrostatic pressure and limit frost movement during the winter.
- Vapor barriers located under floor slabs that are sealed against the footing or base of the foundation wall so that water vapor and radon gas can't get inside the enclosure. Some installations envelope the footing, attaching the membrane to the vapor barrier under the floor slab on the inside and the waterproof membrane on the outside of the foundation.
- Pitching the ground so that rain and landscape water move away from your home.
Installing Sprayable Membranes
Sprayable membranes don't require that concrete be cured before installation. Most applications occur about three days after placing concrete, but they shouldn't be placed on wet walls. Van Wyks, Waldo, Wis., is a concrete construction company that installs 500 to 600 house foundations per year. They also install their own foundation waterproofing. Happy Arpke, the general manager, says they use Tremco's modified asphalt rubber product. “It's a water-based material that must be heated to about 120° F in order to spray properly. If a foundation wall is wet the application can become diluted and if it rains right after spraying, the product can wash off the wall.” He adds that they can install to temperatures as low as 20° F. “After that it's an issue of whether it will cure or freeze.”
Sprayable membrane systems require some preparation to the foundation wall. President of EPRO, Wichita, Kan., Dave Polk says they recommend patching honeycombs, voids, and rock pockets. Walls also should be fairly flat. “Fins” left by form panel seams should be flattened. Polk says there is more concern now to spray the horizontal face of the footing, thus this area must be clean and dry.
Mike Cobb, the general manager of Rub-R-Wall of Ohio, Dublin, Ohio, is a waterproofing installation contractor. He says they can bridge cracks or defects 1/16 inch and less. But concrete contractors are generally responsible for defects ¼ inch and greater. “This leaves a gray area in terms of responsibility,” he says. “And voids of 1/8 inch in width are fairly common.”
It's standard practice now to install protection over the membrane. When local codes require insulation, it becomes part of the protection. Sometimes water drainage systems are included within the protection board. Boards can be attached by placing them against the uncured membrane, by spraying adhesive over the membrane, or by placing the protection against the membrane and holding it in position with backfill material.
Installing Sheet Membranes
Corbett says that contractors who don't own spray equipment often install sheet membranes. “Peel and stick” products make this easy to do and they have the advantage of providing a very consistent mil thickness. And like sprayed membranes they typically extend to the outside edge of the footing. Workers often add mastic or sealant to places where the membrane terminates.
Working on the principle that a complete membrane system should start by eliminating hydrostatic pressure, Cosella Dörken manufactures its product with a dimpled surface on both sides of the membrane. This provides a layer of air between the foundation wall and the membrane that permits water vapor to leave the concrete. Geotextile cloth on the other side allows water to pass into the dimpled space and flow to the drain located alongside the footing. At the bottom of the wall the membrane extends over the edge of the footing to keep the intersection of the footing and wall dry.
Investing In Waterproofing
Marketing is often about “selling the sizzle.” Homebuyers often choose amenities that they can see. They would rather buy a home with granite kitchen countertops, for instance, than spend the money for better insulation or waterproofing. After they move in and start living with the problems, however, complaints and lawsuits against contractors and builders result. But the need to save energy is pushing us into a new age. Air drafts that move outside air right through a house are no longer acceptable, but building airtight homes presents new challenges. Controlling water movement outside the building and water vapor inside (and dew points along wall surfaces) reduces mold growth and should be considered as an amenity worth more than that countertop. Consider a waterproof envelope that includes the slab on grade floor, the footings, and the foundation wall, and use products that limit hydrostatic pressure, moving water away from the building.
Should you install sheet or sprayable membranes?
Jim Corbett, regional manager for Carlisle Coatings and Waterproofing, Wyle, Texas, says “Spraying waterproof membranes is very fast and requires less labor. But when you don't own the spraying equipment, you install sheet membranes.” There isn't a quality difference between the systems; they both provide adequate protection over time.
Most spray membranes advertise that they can bridge 1/16-inch cracks and defects. This isn't an issue for sheet products but surface prep to remove protrusions so that sheets won't get punctured is important. When adhesive-backed sheet products are installed, concrete surfaces must be clean and dry enough for good adhesion.