Damproofing or Waterproofing
By: Christopher Brooks
There has long been a misunderstanding in the construction industry about the terminology used to describe foundation preparation in terms of damproofing vs. waterproofing and the determination as to when each type of preparation would be applied. Experience has shown that most problems associated with foundation preparation (coating) failures were due to inaccurate assessment of the local soil moisture conditions and improper choices for adequate foundation protection systems to match these conditions.
Photo courtesy of Cosella-Dorken
"The two most misunderstood terms used in the construction industry are damproofing and waterproofing," said Joseph Vaccarella, senior vice president of Cosella-Dorken Products Inc. (www.deltams.com), manufacturers of DELTA-MS and DELTA DRAIN air gap membrane waterproofing products, based in Beamsville, Ontario, Canada. "Let's take a look at what these two terms actually mean and how the systems related to each of the terms really work to protect the foundation of homes and almost every other structure that has a foundation," Vaccarella said.
"Most building codes describe damproofing membranes to be a preparation (coating) that is applied to the exterior surface of foundation walls in areas that are not expected to be subject to hydrostatic pressures due to soil moisture conditions and act to separate usable living space from exterior below ground conditions. These preparations act as capillary breaks to stop the movement (migration) of liquid moisture in the soils from coming into direct contact with the exterior face of the foundation wall system."
Damproofing materials are almost always oil-based and the majority are still in liquid form applied by a spraying or rolling method. There is normally no special detailing required when applying these materials because hydrostatic pressures are not a factor in the coatings ability to perform a capillary breaking function. In addition, the use of damproofing is (contingent) relying on the installation of an adequate foundation perimeter drainage system to assist in controlling any build up of water that might occur in the local soils.
Damproofing materials normally have a relatively low permeance value (ability to resist migration of moisture in soils from penetrating the coating), except in the case of polyethylene, which has a very low permeance value. A permeance (or perm) value is defined as a measure of how quickly water/vapor diffuses through a material, with a vapor retarder (barrier) being defined as a material having a permeance value of 1.0 or lower.
"One of the determining factors affecting the performance of damproofing coatings that are spray applied is an issue of quality control. Most of the manufacturer's stipulate that their product meets a particular perm rating provided that the material is applied to a specific thickness for the application. The application in terms of thickness is generally measured in mils and most finished coatings are in the range of 30 mils to 60 mils wet application with a dry film thickness after curing of 15 mils and up.
Most building codes describe waterproofing membranes to be a preparation (coating/barrier) that is applied to the exterior surface of the foundation walls in areas that are known or are expected to be subject to hydrostatic pressures due to soil moistures conditions. Like damproofing, it separates usable living space in basements from exterior below ground conditions.
"These membranes act not only as capillary breaks to stop moisture contact with the foundation wall, but also provide protection for the foundation from the effects of hydrostatic (water) pressure build up around the foundation from being forced into direct contact with the foundation wall under a hydrostatic head of water, which can leads to major moisture problems for you and your basement."
Experience has shown that failure of waterproofing systems is the result of improper installation and material incompatibilities. This originates from a lack of understanding on the part of the installer to know that application procedure prior to starting the job, in addition to using substitute materials without input from the designer.
Most waterproofing systems employed for foundation protection use some form of drainage/protection layer in front of the waterproofing so the main component is not damaged during the backfilling operation, and reduces the potential for water to penetrate the waterproofing membrane. In almost all cases the installation of a waterproofing system on a foundation wall will perform the functions of damproofing and waterproofing at the same time because of its enhanced features. Installation of waterproofing in areas that are not normally expected to be subject to hydrostatic pressures due to soil moisture is permissible; however, while the cost for this type of installation under these circumstances is a little excessive, it gives the end user some added peace of mind should he ever need the extra protection.
Choosing the right type of foundation protection for your situation requires careful planning and choices that must be considered. Do the proper investigation before hiring an architect or specifier to draw your plans. You can obtain some of the information needed to help you decide on the right protection system for your home by contacting your local building/planning departments or water and natural resources authorities, to get preliminary information about water tables levels, flood zones, and typical soil conditions that you can expect to encounter during construction.
If you don't have the time for this work, Vaccarella advises that you make sure your house designer makes the effort to get the information and include it in his design proposal. Choosing a competent designer to draw your house plans will save you troubles during the construction phase because they are responsible for knowing this type of information prior to designing your home plan.
"The main issue here for homebuyers to consider is, 'buyer beware' and always be sure to investigate where you re building, or in the case of buying a home from a builder, investigate the background behind the area you are buying in to ensure you don't end up with problems you didn't count on," he said. "In addition, your investigation will provide you with a wealth of information about the right foundation protection for your project."
Christopher Brooks is a freelance writer based in Bucks County, Penn., writing about the home for consumer and trade magazines.