De Realtà Mapei n.° 34 - 9/30/2021
A Q&A session with one of MAPEI’s waterproofing experts
We sat down with Harold Hays, MAPEI’s Technical Services Manager – Waterproofing, to get to the bottom of the topic of waterproofing elevator pits. We asked, and he answered. From the very basics to top-level advanced, this article covers a range of information. You may already know the answers to some of these questions, but, as codes have changed through the years as quickly as elevator speeds, some of the information may be surprising.
RMNA: Let’s start with the basics: What is an elevator pit, and why does it need waterproofing?
HH: Simply put, an elevator pit is the bottom part of the elevator shaft that extends below the floor slab of the lowest occupied space. The pit usually extends a minimum of 5 feet below the floor slab in order to accommodate elevator equipment, which extends below the elevator so it can operate. The depth of the pit also allows space for the force of the elevator cab when it returns to the lowest floor. The pit must remain dry to prevent the equipment from exposure to moisture, which can cause rust, malfunctions, and premature wear and tear. Moisture in the elevator pit can also promote mildew and mold, and lead to the deterioration of the building’s foundation.
Elevator pits are not the only pits found in structures that need to be waterproofed. Other pits that need waterproofing include pits required for escalators, dumbwaiters, moving walks, as well as for material lifts and equipment.
RMNA: How does water/moisture get into the elevator pit, and what can be done to keep it out?
HH: Water/moisture can enter the pit by different means. Water will find its way in through cracks in the pit’s walls or slab. Water can also enter through concrete joints such as where the wall meets the footing, pipe penetrations, tie-rod holes for concrete wall forms, and around the elevator plunger in the slab.
Used to build walls, concrete masonry units (CMU) are so porous that water can easily migrate through them and through the mortar joints. If there is hydrostatic pressure caused by a high water table or a perched water table, the pressure will force the water in through any crack or crevice. Water tables are not flat and can fluctuate with the seasons due to rain and snowfall. Rainwater can find its way in through cracks. Most construction projects will have a geotechnical report provided by a geotechnical engineer showing where the water table is located and providing an estimate of historical highs that will show if the water table will come in contact with the proposed building’s foundation and pits. The report will determine if there is a need to install waterproofing under the elevator pit slab, footings and walls, or just the walls. The rule of thumb is that it is always safest to err on the side of caution when installing an elevator pit and to also install a waterproofing system.
RMNA: Should all elevator pits have waterproofing?
HH: Yes. Waterproofing will help to reduce the chance of mold, mildew and smells, structural issues, along with elevator equipment issues related to moisture. Mildew and mold need a water source to live and can be hazardous to human health, and can cause smells or odors in the elevator shaft that transmit to the occupants of elevator cars. Moisture can cause rusting of steel reinforcing in the footings, walls and slab which will compromise the structural integrity of the foundation. Because of these reasons, building codes now mandate the use of waterproofing on building structures/foundations below-grade. The code for elevators is The American Society of Mechanical Engineers (ASME) A17 and can be found at www.asme.org. This code requires that waterproofing be used and that the elevator pit be dry.
RMNA: What is the typical material used in elevator pit construction?
HH: The pits can have concrete footings with poured-in-place concrete or CMU walls and a concrete floor slab poured at the interior. Or, the pits can be constructed with a mat slab and the poured-in-place concrete or CMU walls sit on top. A mat slab is a concrete slab poured to the thickness of a footing and featuring the strength of a footing. This combination of thickness and strength supports the pit walls. These type of pits are built, then soil is backfilled around the pit and compacted.
Pits can also be constructed using blindside construction. With this type of construction, a hole is dug in the ground and the waterproofing is installed – first across the bottom of the hole and then up the sides of the hole. Then, a mat slab is poured. Next, the poured-in-place walls are formed using only forms on the interior side of the pit and using waterproofing attached to the soil walls as the outside forms are permanent. This construction is called blindside waterproofing because after the slab and walls are poured, the waterproofing cannot be seen.
RMNA: Where should the waterproofing system be located? On the exterior or the interior of the pit?
HH: If the waterproofing is installed on the inside of the pit, it is called negative-side waterproofing. If it is installed on the exterior of the building, it is called positive-side waterproofing. Negative-side waterproofing does not protect the substrate because it allows water to enter the substrate (footings, walls and slab). Water in the substrate can make the reinforcing steel rust and affect the structural integrity of the substrate.
Positive-side waterproofing locates the waterproofing system on the exterior side of the substrate so that it is positioned between the water and the substrate so that the water will never touch or even have an opportunity to get into the substrate. This is the most effective way to waterproof a building. Also, waterstops should be used in cold concrete pour joints. Cold concrete pour joints occur when concrete is poured to a certain point and is stopped but is not finished. The concrete will set up and get hard before the next section is poured. This will make a tiny crack between the poured sections through which moisture can travel. A waterstop should also be used around penetrations that travel through walls and slabs. When concrete is poured around a penetration and it cures, then a tiny crack will form between the concrete and around the penetration.
RMNA: We’ve heard the term “dampproofing” used. Is it the same thing as waterproofing?
HH: No. They are not the same. Waterproofing is defined by ASTM as “the treatment of a surface or structure to prevent the passage of water under hydrostatic pressure.” Dampproofing is defined as “the resistance of water in the absence of hydrostatic pressure.” Dampproofing materials will not bridge cracks in concrete or move with the building structure like waterproofing materials.
RMNA: What are the characteristics of a primary waterproofing system?
HH: A waterproofing system must be effective against moisture intrusion, continuous, durable during construction, and last for the life of the building. The waterproofing system must have all the necessary accessories to be a complete waterproofing system. Most of all, the waterproofing system should be properly installed by a reputable contractor – approved by the waterproofing manufacturer – who is familiar, not only with waterproofing in general, but also with the waterproofing system to be installed.
RMNA: What are the characteristics of a waterproofing manufacturer?
HH: A good waterproofing manufacturer has been producing waterproofing for more than five years and has several different waterproofing products with accessories to make a complete waterproofing system. The manufacturer should make all the literature, SDSs, specifications, standard details and installation instructions readily available. The manufacturer should have a technical services department that can answer questions about their products and how to install their products, project document review, waterproofing recommendations and design, provide project specific CAD details, and help with project submittals. They should have someone available for jobsite visits, pre-construction meetings, on-site problem resolutions, and to provide product training for waterproofing contractors, distributors and architect/consultants. And lastly, the manufacturer should furnish warranties covering the waterproofing system.
RMNA: What type of systems can be used to waterproof pits?
HH: First, there are a few different types of waterproofing that can be used to waterproof a pit:
- Liquid-applied systems,
- Self-adhered sheet membranes,
- Sodium bentonite clay, and
- Pre-applied chemically/mechanically adhered sheet membranes.
All these different types of waterproofing solutions have accessories to go along with them to make a complete waterproofing system, and MAPEI offers all of them. They all have different applications.
The liquid-applied membrane (Planiseal CR1) and self-adhered sheet membranes (Mapethene HT and Mapethene LT) can only be used for post application on backfill walls.
Sodium bentonite clay (Mapeproof HW and Mapeproof SW) can be used for post application on backfill walls and blindside waterproofing applications.
Pre-applied, chemically/mechanically (Mapeproof FBT) adhered sheet membrane can only be used for blindside applications.
Often the application of a waterstop in concrete control joints and around penetrations is forgotten. Typically, a bentonite rope (Idrostop B25) that swells when exposed to moisture is used.
Planiseal CR1 is a cold-applied, 100%-solid, solvent-free, polyether, liquid waterproofing. Polyether will not revert from long-term exposure to water like polyurethane waterproofing products. It can be applied horizontally or vertically by roller, squeegee or brush. The accessories are MAPEI LMR Fabric and a variety of sealants, including Mapeflex PU40, Mapeflex P2 NS, Planiseal CR2-V and Mapedrain drainage composites.
Mapethene HT and Mapethene LT are composed of 56 mils of rubberized asphalt laminated to a 4-mil cross-laminated polyethylene (HDPE) film with a tear-resistant, silicone-coated release paper. Mapethene HT ’s formulation is for applications installed at 40°F (4°C) and above. Mapethene LT’s formulation is for applications installed between 25°F to 60°F (-4°C to 16°C). Accessories for Mapethene HT/LT include Mapebond 710 and Mapebond 720 primers/contact adhesive, Mapeflex P2 NS, Mapethene Mastic, and Mapedrain drainage composites.
Mapeproof HW and Mapeproof SW are made with two polypropylene geotextile fabrics, one woven and one nonwoven, with 1.13 pounds of sodium bentonite clay sandwiched between the two. Mapeproof HW is used where the groundwater is not contaminated. Mapeproof SW is used where it could be exposed to saltwater or contaminated water or on contaminated jobsites. The accessories for these sheet waterproofing membranes include Mapeproof Granules, Mapeproof Sealant and Mapedrain drainage composites.
Mapeproof FBT is made of a nonwoven polypropylene fabric laminated to a FPO sheet for a total thickness of 67 mils (1.7 mm). The accessories are Mapeproof FBT Tape, Mapeproof BA Tape, Mapeproof Fix Tape, Mapeproof SA Tape and Mapedrain drainage composites.
General accessories for waterproofing are Planitop X for concrete substrate repair and Idrostop B25 waterstop for protecting concrete cold-pour joints and penetrations through the slab and walls.
MAPEI offers one product for negative-side (inside the pit) waterproofing: Planiseal 88. This can be used when an already constructed pit has no waterproofing or when other moisture-related problems arise. However, negative-side waterproofing is by no means the correct way to waterproof a pit.
RMNA: Thank you for all of this information, Harold. You’ve given us a lot. If there are key points to remember for maintaining a dry elevator pit, what are they?
HH: Remember that the elevator code, The American Society of Mechanical Engineers (ASME) A17, requires the elevator pit to be dry and mandates the use of waterproofing. Waterproofing will prevent the passage of water under hydrostatic pressure, and dampproofing will only resist water under normal conditions. Use a waterproofing membrane with accessories to make a complete system and be sure that it is installed by an approved waterproofing contractor.
Always waterproof a pit when it is being built, because you have one shot to do it right and that’s the first time. There is an old saying that says it all: “1% of a building’s costs are used for waterproofing... and 95% of a building’s problems relate to waterproofing!” I think that really says it all!