DETAILING SANDWICH MEMBRANES

Expansion or control joints should be installed in both the structural slab portion and the protection layer. Providing for expansion only at the structural portion does not allow for thermal or structural movement of the topping slab.

This can cause the topping slab to crack, leading to membrane deterioration. Refer to Figs. 3.62 and 3.63 for proper detailing. Membranes should be adhered only to the structural deck, not to topping layers, where unnecessary stress due to differential movement between the two layers will cause membrane failure.

FIGURE 3.62 Expansion joint detailing for topping slab construction.

FIGURE 3.63 Expansion joint detailing for topping slab construction.

Waterproof membranes should be adequately terminated into other building enve- lope components before applying topping and protection layers. The topping is also tied into the envelope as secondary protection.

Control or expansion joints are installed along topping slab perimeters where they abut other building components, to allow for adequate movement (Fig. 3.64). Waterproof membranes at these locations are turned up vertically, to prevent water intrusion at the protection layer elevation. Refer to Fig. 3.65 for a typical design at this location.

FIGURE 3.64 Perimeter expansion joint detailing for sandwich-slab membranes.

FIGURE 3.65 Transition detailing for sandwich-slab membranes.

When pavers are installed as the protection layer, pedestals are used to protect the membrane from damage. Pedestals allow leveling of pavers, to compensate for elevation deviations in pavers and structural slabs (Fig. 3.66).

FIGURE 3.66 Pedestals permit the leveling of the walking surface on sloped structural decks
using sandwich-slab membranes.

At areas where structural slabs are sloped for membrane drainage, pavers installed directly over the structural slab would be unlevel and pose a pedestrian hazard.

Pedestals allow paver elevation to be leveled at these locations. Pedestals are manufactured to allow four different leveling applications, since each paver typically intersectsfour pavers, each of which may require a different amount of shimming (Fig. 3.67).

FIGURE 3.67 Pedestal detail.

If wood decking is used, wood blocking should be installed over membranes so that nailing of decking into this blocking does not puncture the waterproofing system. Blocking should runwith the structural drainage design so that the blocking does not prevent water draining.

Tile applications, such as quarry or glazed tile, are also used as decorative protection layers with regular setting beds and thin-set applications applied directly over membranes.

With thin-set tile installations, only cementitious or liquid-applied membrane systems are used, and protection board is eliminated. Tile is bonded directly to the waterproof membrane.


Topping slabs must have sufficient strength for expected traffic conditions. Lightweight orinsulating concrete systems of less than 3000 lb/in2 compressive strength are not recommended.

If used in planting areas, membranes should be installed continuously over a structural deck and not terminated at the planter walls and restarted in the planter. This prevents leakage through the wall system bypassing the membrane. See Fig. 3.68 for the differences in these installation methods. Figure 3.69 represents a typical manufacturer detail for a similar area.

FIGURE 3.68 Planter detailing for split-slab membrane.

FIGURE 3.69 Typical detail for planters on decks.

Using below-grade membranes for above-grade planter waterproofing is very common, especially on plaza decks. While these decks themselves are often waterproofed using the techniques described in this chapter, the planter should in itself be made completely water- proof to protect the building envelope beneath or adjacent to the planter.

Figures 3.70 and 3.71 detail the typical application methods of waterproofing above- grade planter areas. Note that each of these details incorporates the use of drainage board to drain water towards the internal planter drain. Since these areas are watered frequently, drainage is imperative, in this case, not only for waterproofing protection but also for the health of the vegetation planted in the planter.

FIGURE 3.70 Typical detailing for above-grade planter areas.

FIGURE 3.71 Typical detailing for above-grade planter areas.

Figure 3.72 shows the application of liquid membrane to planter walls as does Fig. 3.73. In the latter note how difficult the use of a sheet good system would be in this particular application. Whenever waterproofing above-grade planters with tight and numerous changes-in- plane or direction, liquid applied membranes are preferred over sheet-good systems as the preferred “idiot-proof” application. The con- tinual cutting of sheets in these smaller appli- cations results in a corresponding number of seams that emphasize the 90%/1% principle. Liquid applications are seamless and can prevent the problems associated with sheet-good installation in small planter areas.




Selection of a protected system should be based on the same performance criteria as those for materials used with below-grade applications. For example, cementitious systems are rigid and do not allow for structural movement. Sheet-goods have thickness controlled by premanufacturing but contain seams; liquid-applied systems are seamless but millagemust be controlled.

DRAINAGE REQUIREMENTS

Protected membranes are used for swimming pool decks over occupied areas, rooftop pedestrian decks, helicopter landing pads, parking garage floors over enclosed spaces, balconies, and walkways. Sandwich membranes should not be installed without adequate pro- vision for drainage at the membrane elevation; this allows water on the topping slab, as well as water that penetrates the protection layer onto the waterproof membrane, to drain (Fig. 3.56). If this drainage is not allowed, water will collect on a membrane and lead to numerous problems, including freeze–thaw damage, disbonding, cracking of topping slabs, and deterioration of insulation board and the waterproof membrane. Refer to Figs. 3.57 and 3.58 for an example of these drainage requirements.

FIGURE 3.56 Prefabricated drainage layer in sandwich application. Note the insulation is spaced to
permit drainage also.

FIGURE 3.57 Dual drain installed for proper drainage of protected membrane level.

FIGURE 3.58 Schematic view of drainage requirements for sandwich-slab membranes.

For the best protection of the waterproofing membrane, a drainage layer should be installed that directs water to dual drains or terminations of the application. Water that infil- trates through the topping slab can create areas of ponding water directly on top of the membrane even if the structural slab is sloped to drains.

This ponding can be created by a variety of causes, including imperfections of the topping slab and protection layer, dirt, and debris.

To prevent this from occurring and to ensure that the water is removed away from the envelope as quickly as possible, a premanufactured drainage mat should be installed on top of the waterproofing membrane. The drainage layer can also be used in lieu of the protection layer.

However, the sandwich membrane drainage systems have one major difference: they are produced with sufficient strength to prevent crushing of the material when traffic, foot or vehicular, is applied after installation. A typical drainage mat is shown in Fig. 3.59.

It is imperative that termination detailing be adequately included to permit the drainage or weeping of water at the edges or perimeter of the sandwich slab installation. This is usually provided by installing an edge-weep system and counter-flashing, as shown in Fig. 3.60. Or if the structural slab is sloped to drain towards the edges of the slab, a drain and gutter system should be provided as shown in Fig. 3.61.

Note that in each of these details the drainage is designed to sweep water directly at the pre- fabricated drainage board level. The drainage board should be installed so that the channels created are all aligned and run towards the intended drainage. The entire purpose of the various drainage systems in a sandwich-slab application (drainage mat, deck drains, and edge drainage systems) can be entirely defeated if the pre-fabricated drainage board is not installed correctly.

FIGURE 3.61 Drainage system detailed into gut-
ter system.

PROTECTED MEMBRANES - WATERPROOFING PROTECTION

With certain designs, horizontal above-grade decks require the same waterproofing protection as below-grade areas subjected to water table conditions. At these areas, membranes are chosen in much the same way as below-grade applications. These installations require a protection layer, since these materials cannot be subjected to traffic wear or direct expo- sure to the elements. As such, a concrete topping slab is installed over the membrane, sandwiching the membrane between two layers of concrete; hence the name sandwich-slab membrane. Figure 3.51 details a typical sandwich-slab membrane.

FIGURE 3.51 Typical sandwich-slab membrane detailing. (Courtesy of TC MiraDRI)

In addition to concrete layers, other forms of protection are used, including wood decking, concrete pavers (Fig. 3.52), natural stone pavers (Fig. 3.53), and brick pavers (3.54). Protected membranes are chosen for areas subjected to wear that deck coatings are not able to withstand, for areas of excessive movement, and to prevent the need for excess maintenance. Although they cost more initially due to the protection layer and other detailing required, sandwich membranes do not require the in-place maintenance of deck coatings or sealers.

FIGURE 3.52 Protected membrane application using concrete pavers. (Courtesy of American Hydrotech)

FIGURE 3.53 Protected membrane application using stone pavers. (Courtesy of TC MiraDRI)

FIGURE 3.55 Insulation layer in protected membrane application. (Courtesy of American Hydrotech)

Protected membranes allow for installation of insulation over waterproof membranes and beneath the topping layer (Fig. 3.55). This allows occupied areas beneath a deck to be insulated for environmental control. All below-grade waterproofing systems, with the exception of hydros clay and vapor barriers, are used for protected membranes above grade. These include cementitious, fluid-applied, and sheet-good systems, both adhering and loose-laid. Additionally, hydros clay systems have been manufactured attached tosheet-good membranes, applicable for use as protected membrane installations.

FIGURE 3.55 Insulation layer in protected membrane application. (Courtesy of American Hydrotech)

CLEAR DECK SEALERS - BUILDING

Although similar to vertical surface sealers, clear horizontal sealers require a higher percentage of solids content to withstand the wearing conditions encountered at horizontal areas. Decks are subject to ponding water, road salts, oils, and pedestrian or vehicular traffic. Such in-place conditions require a solids content of 15–30 percent, depending on the number of application steps required. Typically, two coats are required for lower solids material and one coat for 30 percent solids material. In addition, complete sub- strate saturation is required rather than the spray or roller application suitable for vertical installations.

Clear wall sealers differ from elastomeric coatings in much the same way that clear deck sealers differ from deck coatings. Clear deck sealers cannot bridge cracks in a substrate, whereas most deck coatings bridge minimum cracking. Clear sealers can be applied only over concrete substrates, whereas deck coatings can be applied over metal and wood substrates. Clear sealers are penetrating systems, whereas deck coatings are surface sealers.

Unlike clear sealers for vertical applications, the chemical composition of horizontal deck sealers is limited. It includes silicone derivatives of siloxanes and silanes and clear urethane derivatives. The majority of products are siloxane-based.

A sodium silicate type of penetrating sealer is available. This material reacts with the free calcium salts in concrete, bonding chemically to form a dense surface. The product is typically used as a floor hardener, not as a sealer. Sodium silicates do not have properties that sufficiently repel water and the chlorides necessary for protecting concrete exposed to weathering and wear.

To ensure sealer effectiveness to repel water, test results such as ASTM C-642, C-67, or C-140 should be reviewed. Reduction of water absorption after treatment should be over 90 percent and preferably over 95 percent. Additionally, most sealers are tested for resistance to chlorides to protect reinforcing steel and structural integrity of concrete. Tests for chloride absorption include AASHTO 259 and NCHRP 244. Effective sealers will result in reductions of 90 percent or greater.

Penetration depth is an important consideration for effective repellency and concrete substrate protection. As with vertical sealers, silanes with smaller molecular structure penetrate deepest, up to 1 /2 in. Siloxanes penetrate to a depth of approximately  1/ 4 – 3/ 8 in.

Urethanes, containing higher solids content, penetrate substrates approximately  1/ 8 in.

Silicone derivative sealers react with concrete and atmospheric humidity to form a chemical reaction bonding the material to a substrate. This provides the required water repellency.

Substrates can be slightly damp but not saturated for effective sealer penetration. Over dense, finished concrete, such as steel-troweled surfaces, acid etching may be required.

Since sealers are not completely effective against water-head pressures and do not bridge cracks, proper detailing for crack control, thermal and differential movement, and detailing into other envelope components must be completed. Expansion joints, flashings, and counterflashings should be installed to provide a watertight transition between various building envelope components and deck sealers.

Clear deck sealers are often chosen for application on balconies and walkways above  grade (not over occupied spaces) as well as for parking garage decks. In the latter, the upper deck or lower decks, which cover occupied areas, are sealed with deck coatings, while intermediate decks are sealed with clear sealers. (See Table 3.22.)