Damproofing Versus Waterproofing
By: Christopher Brooks
Damproofing versus waterproofing. Which should you use in your next project? Some products are approved as waterproofing, others are approved as damproofing. This does not mean that one product is better than another.
Photo courtesy of Armtec Ltd.
It simply means that each plays an important, but different, role within building codes in new home construction.
Different manufacturers have varying thoughts about which approach is best. "Homeowners — and builders — can't afford not to waterproof," said Brett Oakley, president of Mar-Flex Waterproofing & Basement Products Inc. in Middletown, Ohio.
Mar-Flex (www.mar-flex.com) manufactures Mar-Flex 5000, a polymer-based asphalt membrane that, when applied over almost any substrate, protects the structure and prevents erosion and deterioration due to moisture or excess water.
The membrane has permanent elasticity, which provides elongation and recovery properties and allows the waterproofing membrane to move with a structure when it settles.
"With today's high volume of moisture, which provides a breeding ground for mold and mildew, waterproofing the foundation eliminates the risk of water infiltration which contributes to these problems."
Oakley shares his thoughts on waterproofing versus damproofing:
* Waterproofing has permanent elasticity to bridge cracks over time.
* Damproofing has no elongation.
* Waterproofing, depending on the quality of the product, has a life expectancy between 5 and up to 100 years.
* Damproofing has a life expectancy between 18 months and up to 3 years.
* Waterproofing is applied to a thick coat of at least 40 mils build up.
* Damproofing is applied to a thin coat.
For years many building codes have required a minimum damproofing application consisting of an unspecified thickness of bituminous tar.
"This is usually formulated with petroleum as the solvent and now, due to environmental concerns, with water — hastily applied to foundation walls," said Pieter Greidanus, Platon Sales - USA.
Platon is manufactured by Armtec Ltd (www.systemplaton.com) in Orangeville, Ontario, Canada, and is an air-gap waterproofing system that is effective for all types of foundation.
It is a tough, dimpled, 24-mil high-density polyethylene wrap that seals out water and bridges foundation cracks.
"Traditionally, as long as the foundation is 'black,' it's damproofed. The consistently poor performance of these products has given the term 'damproofing' a bad name. So no wonder everyone prefers to use the word 'waterproofing.'Practically speaking, unless the water table is higher than your home's footings, all you really need is damproofing to comply with most building codes. If you're building in an area where the foundation is below the water table, it must be specially designed to withstand the extreme forces exerted by ground water, as the foundation will literally try to float. A regular foundation design is not suited structurally for this application and the services of an experienced engineering firm are a must."
Greidanus said that because the vast majority of residential foundations are built above the ground water table, under most building codes they require only damproofing. The use of true waterproofing in such applications amounts to over design and excessive expenditure and gives you no better protection than you could expect from a good damproofing system.
"In order to be effective, products that are 'true' waterproofing membranes (they are usually elastic so they will bridge cracks) must be carefully applied under 'ideal conditions' by skilled applicators using special equipment," he said. "The walls must be dry if petroleum is used as the solvent or free of oil — used on poured concrete walls as the form release agent — if water is the solvent. As well as requiring multiple coatings, elastic membranes should be used with protection boards to prevent backfill damage to the membrane. They are, therefore, expensive.
"Elastic membranes without protection boards sometimes fail to bridge larger cracks (over one-sixteenth of an inch) because wet soil pushes the materials into the crack. If the crack has any sharp edges, the material punctures. Elastic membranes also force the water used to make the concrete (15 gallons per cubic yard of concrete) to evaporate into the basement and the walls can take years to dry out."
Even if your foundation is built above the ground water table and during a heavy or prolonged rainfall event, the footing drainage system or the sump pump cannot keep up with the flow, waterproofing on the foundation wall may prevent the walls from leaking.
However, because water always finds its own level, it will come up through the floor. No matter what you have on the walls, a good working foundation drainage system is a must.
Air gap membranes
Greidanus said using air gap membranes is the best approach. An air gap membrane is a tough, dimpled, waterproof, high-density polyethylene sheet that is unrolled horizontally along the foundation wall and mechanically fastened to it along the top of the membrane. Because it rests on the wall and is not adhered to it, the wall can shift, crack and settle over the life of the structure without affecting the membrane or its performance.
Air gap membranes will easily bridge a quarter-inch crack and have successfully kept water out with a 1-inch crack. "The dimples form an air gap between the wall and the soil so that if any water does manage to get past the membrane, it will flow to the footing drain, not into the basement. As an added benefit, moisture in the wall will condense on the back of the membrane (instead of evaporating into the basement) and flow to the footing drain so the potential for mold and mildew growth is minimized right from the start."
Air gap membranes can also be used under a concrete floor to permanently prevent moisture from wicking up through the slab, because unlike builders' polyethylene, they are unaffected by the alkaline in concrete and are tough enough to withstand concrete placement without damage.
Air gap membranes are approved as either waterproofing or damproofing.
"While more expensive than tar, they are less expensive than most elastomeric waterproofing membranes and definitely outperform both. Used in Europe for more than 30 years, the technology was brought into North America in 1991," Greidanus said. "Builders and homeowners alike simply don't have to worry about basement wall leaks when they have an air gap membrane protecting their foundation."
Christopher Brooks is a freelance writer based in Bucks County, Penn., writing about the home for consumer and trade magazines.