Floors and slabs
Concrete floors and slabs should also be properly waterproofed from the positive (or under) side as they are a component of the foundation. Occasionally, the underside waterproofing will fail if improperly selected or installed, causing water to seep through the floor slab. The addition of a negative-side waterproofing application can forestall an expensive or potentially impossible repair. It is recommended to choose a negative-side waterproofing product specifically designed for use on horizontal surfaces that will block the hydrostatic pressure forcing water up through the floor. Depending on the specific location, the chosen waterproofing material may need to handle foot or vehicular traffic. Adding tints and non-skid additives to liquid acrylic waterproofing materials can also offer decorative and safety advantages.
Installing a negative-side waterproofing material to a concrete floor or slab also creates a moisture barrier underneath flooring materials such as tile, carpet, or wood. Using a liquid acrylic latex-based waterproofing material assures compatibility with other latex-based flooring adhesives.
Negative-side waterproofing retrofit: A case study
Moisture intrusion was detected at the Brevard County Courthouse in Viera, Florida, due to water damage and mold on the gypsum board. A fast, easy-to-use, cost-effective method was needed to provide a masonry patch and moisture mitigation solution on the interior and exterior of the courthouse without a major renovation. The moisture had intruded through gaps between concrete masonry unit (CMU) block columns that were poorly tied into face brick returns at the window openings. An existing negative internal pressurization of the structure, aggravated by strong coastal wind-driven rain, pushed moisture through the exterior wall gaps, thereby causing condensation on the interior steel gypsum board studs.
Prior to any patching and waterproofing activities, the negative pressurization issues in the building were solved.
Hydraulic cement was then used to fill the gaps between the returned face brick and the concrete columns on the interior (negative side) of the building exterior walls on the third and fourth floors. Backer rod was inserted into deeper gaps and filled with a concrete patch.
After completing patching, two coats of a latex-based masonry waterproofer were applied on the interior side of the walls, over the patches, and around the windows. In the author’s experience, the material provides a long-term barrier to both casual moisture and wind-driven rain intrusion along with sealing the recently applied patching materials.
A mockup area was first repaired and tested by Intertek PSI, the project’s consultants. A professional high-pressure spray rig was utilized to simulate wind-driven rain conditions. The mockup preformed as expected, and the complete project repair commenced.
All the repairs were completed within a few weeks, and the courtrooms and judges’ chambers were restored to their original interior finish condition.
Conclusion
Negative-side waterproofing is another tool designers and specifiers can use in order to keep spaces dry and protected in new construction. Choosing the correct waterproofing barrier position or a combination of settings can protect a building for life. Negative-side waterproofing can also be invaluable if the original waterproofing installations fail, or interior (dry side) protection is the only solution.
Designers and specifiers must consider the individual project circumstances and chose the best option for their needs. Manufacturers are always available to consult on what may be a selection of solution options, and what has worked for them in the past. They can also share job-specific instances to provide more confidence in the selection of the right solution for the specific need.
Harry J. Lubitz, CSI, CDT, is the architectural sales director for the United Gilsonite Laboratories, Inc. Lubitz has more than 30 years of experience in the building materials industry, is active in numerous architectural and professional organizations including CSI. He has served as an adjunct faculty member at Lord Fairfax Community College in Virginia. Lubitz can be reached at harry.lubitz@ugl.com.
