One Can Select From The Five Basic , Types Of Waterproofing Materials
To the untrained eye, the simple masonry planter boxes wrapping the corners of a new Building, appear innocent enough. But during design, the real professional designer cannot take it lightly. The designer has to imagine the contents of the planters-the soil, plant roots, and, most important, the water-all pushing against the masonry pilasters that highlight the corners of the building and form the inside walls of the planters. The contents of those seemingly innocuous planters could pose a very real threat to the building’s longevity and structural performance.
There is however a simple solution : pillars and plasters with three-foot-wide swaths of self-adhering rubberized asphalt with a polyethylene backing.
To complete the system, use a rigid-foam insulation panel to protect the waterproofing membrane during construction and, later, from the soil added to the planter boxes. The insulating panel also divert water from the masonry pilasters, while solid grouting of the concrete masonry units helps block moisture infiltration.
All this effort for a few planter boxes? Yes. Masonry wants to absorb water so we have to take precautions. These days all over Europe, similar systems can be found on the walls of building foundations with usable subsurface space-most often parking garages-and underneath flooring and elevator pits, among other applications. Development along the city’s riverfront often necessitates waterproofing below grade. Or, like the Spectrum View planters, for special applications aboveground.
An architect’s selection of a waterproofing system should consider the foundation wall material, expected performance qualities of the waterproofing material, and the use of the belowgrade space-many codes require waterproofing if the underground space is habitable.
Other factors include the waterproofing membrane’s functionality in temperature extremes, its vapor permeability, the quality of the substrate, problems with protecting the material during construction, and, of course, cost considerations. Architects also need to be cognizant of regional differences and levels of acceptance before specifying a system.
Soils engineer should be consulted to determine the types of soil that are present and how they will impact the system’s performance, while a waterproofing consultant offers guidance on problem soils.
There are five general categories of waterproofing materials:
Rubberized asphalt sheet membranes; bentonite clay; asphalt, mastic; PVC or high- density polyethylene sheet membranes; Surface-bonding cements, which consist of glass fibers and Portland cement, are often classified as waterproofing systems. But these are used more often to keep water in-for example on the inside surfaces of swimming pools, cisterns, and water- holding tanks.
Sheet membranes are most widely used in vertical applications because they have seams through which standing water can penetrate.
Liquid solutions, which are seamless, are more suited to horizontal applications, such as plazas or decks. Most of the materials come with accessories, including fasteners used to apply sheet membranes, surface-preparation solutions, and slender tapes used to waterproof tight areas, corners, or seams.
The self-adhering rubberized asphalt membranes are most commonly used waterproofing material, accounting for nearly 40 percent of the market, even today – when the chemical treatments and fancy water proffing compounds are trying to make their mark. Bitumne is practically synonymous with rubberized asphalt. Bitumane and its iterations are formulated for application on dry, cured concrete walls and when the temperature is above 40 degrees F.
That means the membrane may not be applied for up to as many as 30 days after the concrete is poured, depending on the speed at which the concrete cures (dictated by outside temperatures and the nature of the concrete mix). Once the forms are stripped away, the surface accepting the membrane must be made smooth and monolithic to prevent spalls, tie wires, honeycombs, or other irregularities from interrupting the membrane’s continuous seal.
This additional step further slows the construction schedule and adds costs. Once laid, the membrane must be protected from direct sunlight, rain, and other environmental conditions which degrade it until the backfill, wearing slab, or other covering is added.
Special primers and formulations are increasingly available for colder conditions, as well as for use with unusual soil conditions.
But for the most part, the membrane is best reserved for moderate climatic conditions and on smooth surfaces.
Bitumane, technically referred to as sodium bentonite, is a naturally expanding clay that may be troweled or sprayed on, or, more commonly, encased in layers of cardboard or geotextile and mechanically fastened to the substrate. Bitumane’s chief advantage is that it can be put over a concrete surface almost immediately after the forms are pulled, which helps speed the construction schedule. It also does not have the climatic limitations of rubberized asphalt, though the material or cardboard panels should not be exposed to rain or snow. Bitumane is somewhat permeable, allowing moisture vapor to migrate through walls and condense on interior surfaces. The vapor can cause damage and odor over time.
Bitumane enclosed between layers of geotextiles is the most practical (and expensive) version of the product since the carpet-like sheets are difficult to puncture and are flexible enough to go up over lagging and other uneven surfaces. Also, the cardboard that encases some panelized versions will degrade over time, causing the bitumane to erode and leaving the walls completely exposed.
Liquid asphalt, which accounts for about 20 percent of the total market, has two major advantages over its competitors: It is highly elastic, allowing it to bridge cracks and accommodate movement, and it embodies “self-healing” properties, meaning the material will ooze around and seal a puncture from a nail or sharp object. Applying two layers, with a sheet of fibrous matting in between, creates a stronger barrier.
Asphalt is most suited to a horizontal application since the hot liquid, mopped onto a vertical surface, can drip, posing a safety hazard.
Mastics are urethanes modified with various polymers to make them flexible. These are cold-applied, usually by rolling or troweling them onto the surface. They dry to create a hard surface, often eliminating the need for protective board. Mastics are easy to apply, but there is evidence that they become brittle and lose their effectiveness more quickly than asphalt. Both types of fluid membranes are suitable for rough surfaces and tough- detail areas, such as tight interior corners, penetrations, and other conditions that are difficult for sheet membranes to accommodate. But while the thickness of a sheet membrane is factory-controlled, spray-and trowel- applied systems rely on the installer to achieve the desired thickness.
This lack of control makes architects understandably nervous. That’s one reason small players focuses on residential basements and allows the bigger players to focus on commercial construction. Currently only about 10 percent of all new homes include a waterproofing membrane (most have nothing at all). But builders are increasingly offering below-grade space outfitted as an extra bedroom, family room, or home office.
Least common are the single-ply sheets, including PVC and high-density polyethylene. That’s because the materials and their application is expensive, especially if there are a lot of details or horizontal-to- vertical transitions to coax the sheets through. In most cases seams must be heat welded, though installation varies.
A basic system may consist of one of these waterproofing materials combined with site drainage, insulation, a rigid material to protect the membrane from construction fill and, in some cases, a wearing layer or top slab. Adding insulation not only helps protect the membrane, but also mitigates the effects of freeze/thaw cycles and, of course, keeps the interior of the building more comfortable. The addition of a drain panel or subgrade drain tile directs water away from the building.
These are useless if the water level consistently rises above the footings because the drainage channels would be filled with water.
From the inside out
In most cases, waterproofing membranes are applied to the outside, or “positive” side, of the structure. This requires additional excavation around the foundation, a factor that may limit its use with infill and urban projects. “Negative-side” waterproofing, applied to the interior of the wall, is used primarily for water-holding purposes, though it is increasingly called upon when positive-side waterproofing is not possible. By design and necessity such systems allow the water to infiltrate the structure before it is blocked from the interior space.
Often necessary in tunnels, under slabs, when a new building foundation abuts an adjacent structure, or if an existing soil retention system prohibits excavation, negative-side systems involve the application of a waterproofing membrane on the inside of the foundation wall, over compacted soil, or between a mud slab and the structural slab.
A few companies have recently launched products that address the problems inherent in this sort of blind-side application. One solution is a new adhesive that mechanically bonds with the just-poured concrete to create a positive-side membrane-a formula that’s expected to proliferate within the industry in a few years.
Here’s how it works: rubberized asphalt is laid into the formwork before the pour. The adhesive layer, which faces in the direction of the pour, is protected by a thin film that shields it from the elements and allows workers to step on it.
As the concrete is poured, the film and the adhesive bond to it, eversing the normal process of applying the membrane.
Another negative-side solution that, so far, has been used mostly in retrofit situations eschews traditional waterproof membranes and drainage systems altogether. Electro-osmosis technology, by Moisture Solutions International, employs a series of anodes-wires set into the interior surfaces of concrete walls and floors-and a cathode wire embedded in the earth outside the structure, both connected to a central unit mounted on the wall. Low-voltage pulses sent throughout the wires cause water to gravitate toward the cathode and away from the anodes.
This sounds risky and expensive; so far, electro-osmosis technology has been tested and used on government buildings where protection of below- grade storage of records and files is an important consideration.
But the system eliminates the need for excavation, can be set into the slab and wall form work in new construction, and offers easy access to the wall- mounted control unit.
How dry is dry enough?
The first question an architect needs to ask when evaluating a waterproofing system is this: “How waterproof does the building need to be?
Dampproofing, which differs from waterproofing in that it merely prevents water infiltration by capillary action, is often sufficient, especially in porous soils, where water percolates quickly. But faced with the threat of water infiltration or a hydrostatic head, whether from the water table, tidal flow, floods, or aboveground sources, such as fountains, architects must create a waterproofing system.
This is a choice that’s often driven as much by the budget and construction schedule as by the presence of water. You have to find out what the owner’s expectations are.
MOST BUILDING CODES REQUIRE A WATERPROOFING SYSTEM WHEN BELOW-GRADE SPACE IS OCCUPIED.
Dampproofing most often involves simply mopping a layer of coal tar onto the foundation wall. Unlike the various waterproofing membranes, coal tar lacks the ability to bridge small cracks and fissures, gateways for water infiltration. It simply retards water migration instead of sealing off the structure. It also contains compounds that are not environmentally friendly. Other dampproofing options include acrylic latex, polyethylene, and cementitious coatings.
The actual specifications for waterproofing, once the system is decided upon, also play a role in the application and cost. Under normal conditions, architects appreciate the standardization of off-the-shelf waterproofing specs, which free them from detailing the system on paper.
The language calls out the materials, method, and installation per the manufacturer’s recommendation. To a certain degree, you have to rely on the standard specs to get competitive bids. But such standardization is not a license for complacency among architects.
Extreme soil or drainage conditions often require careful attention.
Also all waterproofing systems have their limitations and the implications must be carefully considered.
Keep the water out
At Waterfront Landings, a 320,000-square-foot mixed-use condominium retail project worked with soil and civil engineers to devise a waterproofing system for the project’s belowgrade parking garage. Because this project’s garage slab is at sea level, the architects and engineers designed a series of perforated pipes that direct water that seeps in during high tides to a sump basin, where it is pumped way from the foundation to a nearby sewer drain. The drainage system complements the waterproofing which the architect specified for under the slab and along the belowgrade walls. These are meant to encapsulate the structure and prevent water migration.
The building’s elevator pits, which serve five floors of residential and retail space, also needed special attention to keep water from leaking in and mixing with the lifts’ hydraulic fluid. To ensure a tight seal for each elevator, a layer of Bitumane between a mud slab (installed to provide a solid working surface over unstable soils) and the elevator pit, with the clay-saturated sheets pulled up the walls. It’s really not much of a mystery, You just have to be aware of the conditions.
Exposing the existing waterproofing to achieve a lap joint was not always achievable given the delicate nature of removing the existing structure to expose the old waterproofing. Hot- applied modified asphalt and Bitumane Tape tape are often employed when the size of the lap was not sufficient.
The most complex interface between new and existing construction involved threading new caisson foundations through the subway station. This necessitated the use of multiple waterproofing materials in unique ways.
Recent regulatory policies have banned or severely limited the use of solvent-based waterproofing products, including mastics and primers used to prepare the foundation for waterproofing. Land-use covenants and infill or urban sites often restrict excavation or the ability to install standard, positive-side systems.
Tight budgets and construction schedules may discourage their use as well. All these factors have caused a shift in the industry toward new products for special conditions, a variety of primers, sealants, and other compounds to ease application, and non- or low-VOC mixtures to meet environmental standards, and reduce odor and flammability.
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