ABSTRACT Fluid-applied rubberized-asphalt membranes have a long track record of perfor¬ mance in many roofing and waterproofing systems. These membranes can provide reliable waterproofing protection for several decades, but poorly detailed or defective¬ ly constructed assemblies can be quickly destroyed in service and often require cost¬ ly rehabilitation. Achieving long-term performance requires diligent detailing, careful installation, and continued review to ensure that the designers’ intents are constructible and accu¬ rately implemented in the field. This paper will present practical advice to assist in design and construction of fluid-applied, rubberized asphalt membrane systems, with case studies applicable to a variety of projects to illustrate successful details. SPEAKER Nicholas A. Piteo is a staff engineer with Simpson Gumpertz & Heger, Inc., a nation¬ al design and consulting firm that designs, investigates, and rehabilitates structures and building enclosures. Mr. Piteo has a breadth of experience in investigation, repair, design, and rehabilitation of building envelopes. He has performed numerous facade and roof investigations, for which he also provided new designs. He received his master’s of architectural engineering degree from Pennsylvania State University. Mr. Piteo recently presented, “Traditional Clay Tile Roofing – Investigation and Rehabilitation,” at the RCI 2006 Symposium on Building Envelope Technology. CONTACT INFO: napiteo@sgh.com or 301-417-0999 COAUTHOR Christina M. Terpeluk is a senior engineer with Simpson Gumpertz & Heger Inc., a national design and consulting firm that designs, investigates, and rehabilitates structures and building enclosures. Ms. Terpeluk has experience in investigation, repair, design, and rehabilitation of building envelopes. She received her BS in civil engineering at Johns Hopkins University and her master’s of civil engineering from Cornell University. CONTACT INFO: cmterpeluk@sgh.com or 301-417-0999 Piteo and Terpeluk – 1 54 Proceedings of the RCI 24th International Convention
INTRODUCTION Hot-fluid-applied rubberizedasphalt waterproofing membranes have a long track record of perfor¬ mance in at-grade plaza water¬ proofing applications and are gaining popularity on roofs as designers increasingly strive to provide occupant-accessible roof¬ top plazas with green spaces. These membranes are durable and can provide reliable water¬ proofing protection for several decades. Achieving such durabili¬ ty, however, requires the appro¬ priate system, diligent detailing, a quality-oriented waterproofing contractor, careful installation with a high level of quality control, and timely communication among the designer, manufacturer, and contractor to provide a reliable and durable waterproofing sys¬ tem. Through our experience, we have found that active construc¬ tion administration with frequent or even full-time field observation is critical to the success of hotfluid- applied rubberized asphalt waterproofing membranes. This paper is intended as a primer to supplement the knowledge of designers, applicators, and quali¬ ty assurance personnel for hotfluid- applied rubberized-asphalt waterproofing systems and focus¬ es on the authors’ experiences during a recent project to illus¬ trate challenges, successful con¬ struction phase detailing, and lessons learned. THE PROJECT the the ouilding. The portico is surplaza courtyard. The stairs consist of limestone treads and are with flagstone pavers. The project structure. A large classical portico extends over the main entrance to bound on either side by a brick masonry parapet wall. A plaza at the base of the portico is covered included the replacement of the waterproofing system below the port: co terrace and stairs. The existing portico terrace construc¬ tion men ters. with to a consisted of the following eleits, from interior to exterior: The portico terrace is covered limestone pavers and leads grand stair descending to a rour.ded by eight freestanding masonry columns and two pilas- The building, constructed in 1920s, is a brick masonry • Structural concrete deck • Bituminous membrane • Concrete topping slab, approximately Vz- to 1-in thick • Mortar setting bed, approxi¬ mately 1- to I’A-in thick • Limestone pavers, typically 272-in thick with 5-in thick pavers between portico col¬ umns The existing stair construction consisted of the following ele¬ ments, from interior to exterior: • Stepped structural concrete deck • Bituminous membrane • Brick masonry; approximate¬ ly 2 to 3 wythes thick • Mortar setting bed; approxi¬ mately 1- to P/2-in thick • Limestone treads; typically 5- in thick The owners reported that water had leaked to the interior space below the portico terrace and stairs for many years. As a part of a comprehensive building renovation, the owner retained our firm to design the replace¬ ment of the portico terrace and stair waterproofing system. During the design phase, we recognized that providing contin¬ uous waterproofing around the base of the large marble columns would be a challenge. The base of each column includes a continu¬ ous marble pedestal wrapped around a steel column concealed within the cement plaster col¬ umns. Each pedestal is supported by 5-in-thick limestone pavers. One design option proposed ele¬ vating the marble pedestals in place; another proposed cutting them and removing them in sec¬ tions to turn base flashing up the steel columns. We reviewed waterproofing options and limitations with the owner for each option. Consi¬ dering the architectural signifi¬ cance of the building, portico, and columns, the owners decided that any efforts to move the fragile continuous marble pedestals could result in an unacceptable appearance change or irreversible damage; they selected the option Proceedings of the RCI 24th International Convention Piteo and Terpeluk – 1 55 Photo 1 – Removal of concrete topping over concrete substrate. Note that the existing roofing sys¬ tem consisted of (from interior to exterior) concrete deck, existing waterproofing membrane, con¬ crete topping slab, mortar setting bed, and overburden (not shown). to leave the pedestals in place during the waterproofing work. Considering the existing porti¬ co terrace and stair configuration and column limitations, we rec¬ ommended a hot-fluid-applied rubberized-asphalt membrane system to replace the existing por¬ tico terrace and stair waterproof¬ ing system. Although we based our waterproofing design on con¬ ditions exposed by our field inves¬ tigation, we were not surprised that unanticipated existing condi¬ tions and unique details required some adjustments during con¬ struction to provide a reliable waterproofing system. Some of the challenges faced during the construction of the waterproofing system are described below. SURFACE PREPARATION Hot-fluid-applied rubberizedasphalt is commonly installed on both, existing cast-in-place and posttensioned concrete and, less commonly, on precast concrete. Some hot-fluid-applied rubber¬ ized-asphalt membrane manufac¬ turers also allow membrane installation over panelized sub¬ strates, such as plywood decks or metal decks covered with gypsum sheathing. The challenges of installation on panelized sub¬ strates are beyond the scope of this paper. Surface preparation of the substrate is critical to the success of the waterproofing system. A poorly prepared surface can destroy the membrane bond, and ultimately, the membrane. This project included a previously cov¬ ered cast-in-place concrete deck, which requires some additional time-consuming and costly sur¬ face preparation compared with a new concrete deck. Some of the key surface preparation steps for our existing plaza are described below. Overburden Removal Before installing a new water¬ proofing membrane, workers must first remove the existing overburden and waterproofing membrane to allow evaluation and repair of the underlying sub¬ strate (Photo 1). Removal of some existing membranes, such as coal-tar -pitch, self-adhering rub¬ berized asphalt membranes, or Piteo and Terpeluk – 156 Proceedings of the RCI 24th International Convention Photo 2 – Removal of existing waterp’ roofing membrane on stairs using handheld, scrapers. manufacturers. pingEs require a clean but roughened substrate to achieve proper :- :- Bi ing, was iting deck ur project scarification, or pressure king (at significant risk of bond. Excessively smooth existing concrete decks or residue from prior membranes adhered to the deck will interfere with the bond of a concrete overlay and may require sandblasting, shotblast¬ voids vide Crete slab exis at 01 existing hot-applied asphalt, can be difficult. Workers often try cre¬ ative solutions to remove hotapplied asphalt, but we have seen the greatest success with heavy scraping bars, shovels, chisels, and physical effort (Photo 2). Designs should not require the installation of a new membrane over existing membrane because the existing substrate remains concealed, and recovering an existing leaky membrane is likely to trap moisture, which reduces the durability of the waterproofing system. appropriate surface. brane after expending consider¬ able effort to scrape off residue from the previous waterproofing membrane. available from several Concrete topor proa contopping are Provide a Smooth Surface to Receive the Membrane Hot-fluid-applied rubberizedasphalt membranes should be applied to a reasonably smooth surface. Manufacturers generally recommend a wood float finish in accordance with ACI 301; a steel float or trowel finish is too smooth and compromises the bond of the membrane to the substrate. Both new and existing substrates often require grinding ridges smooth to avoid stress concentrations that leakage) to provide an appropriate substrate. Slope the Substrate Waterproofing membranes should slope to direct water off of the membrane or to drains (Photo 3). Our project did not include drains, but existing drains (and overflow drains) should be reviewed for capacity based on rainfall data contained in the International Building Code or other locally applicable codes. Hot-fluid-applied rubberizedasphalt membranes bond directly to the substrate (i.e., tapered insulation is not appropriate), and therefore, the substrate must pro¬ vide the membrane with slope. A durable, low-slope waterproofing system requires a slope of % in/ ft to provide reliable membrane level drainage. Slopes lower than % in /ft provide little margin for error in concrete placement or long¬ term deflection, provide less reli¬ able drainage, and thereby reduce the durability of the waterproofing assembly. Waterproofing slope can be provided by sloped struc¬ tural framing with uniformly thick concrete or with level formwork Existing or particular¬ ly rough sub¬ strates may require a concrete top¬ ping slab to provide an appropriate substrate . Proprietary concrete re¬ pair mortars that can be used to fill in with a con¬ crete topping to provide a smooth sub- Consult with the con¬ crete topping manufactur¬ er 😮 deter¬ mine appro¬ priate sur¬ face prepara¬ tion require¬ ments. We covered the damage the membrane, or filling depressions and bug holes, which can cause blistering, to provide an strate for the new water¬ proofing mem- Photo 3 – Level showing sloped surface at a stair tread. We added slope with a concrete topping at the stair treads to promote drainage. Proceedings of the RCI 24th International Convention Piteo and Terpeluk – 157 and variable concrete thickness (adding significant weight). Water¬ proofing slopes in excess of ap¬ proximately 2 in/ft require special considerations for overburden and membrane restraint because these slopes can create shear force on the membrane. Vertical surfaces that receive recommend testing the concrete deck and repairs for the presence of moisture. ASTM D 4263 – Standard Test Method for Indicating Moisture in Concrete by the Plastic Sheet Method after a minimum 14-day cure provides one method to test Alternative test methods may also be selected to quantify the moisture levels of the concrete surfaces prior to membrane installation. Concrete surfaces should include at least one mois¬ ture test per 500 sq ft of concrete or concrete repairs. At our project, workers installed the conmembrane are typi¬ cally insulated from overburden shear forces by protection/ drainage layers and frequently do not re¬ quire special consid¬ erations for restraint. The existing con¬ crete substrate below the portico terrace for our project in¬ cluded slope towards the plaza stairs. We placed a uniform lay¬ er of concrete fill on top of the portico pla¬ za and maintained the slope. The exist¬ ing concrete sub¬ strate below the stairs did not include slope, and we added slope towards the flagstone terrace and a foundation drain at the bottom of the stairs, with concrete fill. Cure and Dry the Concrete Substrate crete topping slab and cov¬ ered it with a layer of wet burlap and tarps to cure the concrete. We performed moisture testing at several locations as outlined above until we determined that the concrete was sufficient¬ ly dry after 14 days. Photo 4 – Moisture test according to ASTM D 4263 – Standard Test Method for Indicating Moisture in Concrete by the Plastic Sheet Method. Photo 5 – Removal of dirt and debris from concrete surface using a handheld blower. Water on the sur¬ face and excessive moisture in the concrete results in poor bond and pinholes through the membrane as the vapor passes through the membrane. Foaming of the mem¬ brane during installation indi¬ cates a wet substrate. Manu¬ facturers offer guidance for drying concrete substrates, including a minimum 14-day cure and a rec¬ ommended minimum 28-day cure. The drying of concrete sub¬ strates is highly dependent on environmental conditions and we the moisture levels in concrete. This test consists of sealing a piece of plastic sheeting (approxi¬ mately 18 in. by 18 in.) to the con¬ crete surface (Photo 4). After approximately 16 hours, the sheet is removed and both the sheet and concrete surface inspected. Moisture on either the plastic or concrete surface indicates wet concrete, which requires addition¬ al drying time prior to installation of a hot-fluid-applied rubberizedasphalt membrane. Clean the Surface of the Substrate During the construction process, debris and dirt will settle on the concrete substrate and interfere with the membrane bond. Debris and dirt must be removed from the substrate prior to the application of the mem¬ brane by sweeping and blowing the substrate clean with com¬ pressed air to (Photo 5}. Piteo and Terpeluk – 158 Proceedings of the RCl 24th International Convention Photo 6 – Primer applica¬ tion with a brush. Photo 7 – Primer applied in field of the plaza. Note that the lighter-colored primer at the plaza perimeter is a water¬ based primer for loca¬ tions that will receive self-adhered waterproof¬ ing membrane. PRIMER Manufacturers have long used an asphalt-based primer to bind dust and enhance the bond between the concrete surface and the waterproof¬ ing membrane. These primers must conform to ASTM D 41-85 – Standard Specification for As¬ phalt Primer Used in Roofing, Damp¬ proofing, and Wa¬ terproofing. The primer is installed thinly over the concrete sub¬ strate (between 100 and 600 sq ft/gal depending on porosity and surface texture of the substrate and the selected primer) using a brush, roller, or spray equipment {Photos 6 and 7). Properly ap¬ plied primers frequently dry within three hours. However, weather conditions, such as tempera¬ tures below 68°F and relative humidity higher than 50%, can increase the drying time. On our project, the primer was not diy approximately 12 hours after application, due to the overly thick application and cold tempera¬ tures. Workers left the primer to diy overnight, contrary to manufacturer’s recommendations. After consulting with the membrane manu¬ facturer, we inspected the dry primer for moisture (dew) and blown dust prior to the application of the waterproofing membrane on the following day. Contaminated areas of primer require additional primer. Solvent-based primers, such as the asphalt-based primer installed on our pro¬ ject, are highly volatile and emit strong odors. Solvent-based primers must be sep¬ arated from open flames and other heat sources, and occupants should be separat¬ ed from the primer application to avoid complaints and occupant discomfort. With increasing awareness and regulation of sol¬ vents, manufacturers are starting to intro¬ duce a variety of alternative primers that are more “green.” These alternative primers have a short track record and require care¬ ful evaluation, preferably through mock¬ ups, to evaluate their effectiveness and suitability prior to selection and wholesale Photo 8 – Placement of fabric reinforcement on top of the first coat of membrane. installation. Proceedings of the RCI 24th International Convention Piteo and Terpeluk – 1 59 ’■r- – Photo 9 – Measurement of membrane thickness with pin tester. Note that the pin (not shown) is inserted into the membrane, and thickness is read off the top (arrow). Photo 10 – Fabric embedded in membrane for adhesion test. After the membrane cured, workers pulled the fab¬ ric to observe the fail¬ ure mechanism. The membrane failure occurred within the layers of the membrane. MEMBRANE Hot-fluid-applied, rubber¬ ized-asphalt membranes are constructed in one or two coats, reinforced and unrein¬ forced. We consider reinforced membranes more durable because the reinforcement increases puncture resis¬ tance, decreases cold flow (e.g., under concentrated load), improves crack bridging (i.e. cracks, construction joints, and changes in planes), and provides a thickness gauge for the second coat. We recommend that reinforce¬ ment be spread across the first layer of membrane after initial cooling (Photo 8). If the reinforcement is installed too quickly prior to initial cool, the fabric will melt. A typical completed rein¬ forced hot-fluid-applied rub¬ berized-asphalt membrane is an average of 215 mils thick. The installed thickness is important to membrane durability and the con¬ struction observer, contractor, or manufacturer’s representative should measure the membrane thickness in several locations to verify acceptable thickness prior to installation of the protection sheet. Membrane thickness may be measured with a pin tester or at test cuts in the membrane. Pin testing must be performed in close coordination with the installer so that the test area is immediately recoated to seal the test hole. Consistent with most manufacturers, we recommend one measurement per 100 sq ft (Photo 9). At our project, the contractor successfully mocked up the mem¬ brane within the expected thick¬ ness range while we were on site. The mock-up also included an adhesion test that consisted of embedding a piece of fabric with an exposed pull tab within the membrane (Photo 10). The fabric is pulled until membrane failure to examine the failure mode. Our mock-up pull test failed cohesive¬ ly within the membrane, which indicates that the adhesive bond to the deck is stronger than the cohesive bond between layers of the membrane, which is the desired result of the pull test. An adhesive failure between the membrane and substrate indi¬ cates insufficient bond that requires additional investigation to determine the source of poor adhesion. Different test methods may also be selected to measure numerical adhesion values for comparative purposes. Following the mock-up, the contractor installed the mem¬ brane and a protection layer over the entire deck but failed to install the membrane within the accept¬ able thickness range. We discov¬ ered the thin membrane by per¬ forming several pin tests during our next weekly site visit and pro¬ vided the contractor with the fol¬ lowing options to increase mem- Piteo and Terpeluk – 1 60 Proceedings of the RCI 24th International Convention brane thickness: • Remove the membrane pro¬ tection layer, install addition¬ al membrane to meet the specified thickness, and install a new protection layer. However, removal of a fully bonded protection layer is dif¬ ficult under most circum¬ stances and may not be pos¬ sible in some applications (partial removal is not accept¬ able). • Completely remove the exist¬ ing waterproofing system and install new membrane at the specified thickness. Complete membrane removal can be difficult because the mem¬ brane aggressively bonds to the substrate, but may be necessary for applications with minimal clearances at waterproofing details. • Install new membrane, rein¬ forcement, and protection layer on top of the existing waterproofing assembly with¬ out removal. This option may be desirable for applications with sufficient clearance to accommodate the increased thickness of the membrane assembly, as long as the pro¬ tection layer is otherwise well bonded. At our project, the protection layer was well adhered to the first membrane application, and the contractor installed additional membrane on top of the existing membrane without removal. MEMBRANE ACCESSORIES AND DETAILS A hot-fluid-applied water¬ proofing system requires several accessory materials to complete the assembly. Many difficult waterproofing details occur at transitions between the mem¬ brane and accessory materials. We discuss several difficulties we encountered on our project below. Photo 11 – Neoprene flashings installed at the base of a portico column prior to the application of water¬ proofing membrane. Base flashings turn up and transition between the fluidapplied membrane and rising walls or other surfaces. Base flashings should be installed prior to wholesale deck membrane installation to facilitate seamless integration with the membrane. Base flashings may be installed with a manufacturer’s recom¬ mended adhesive, may be hotfluid- applied asphalt, or may be torch-applied. They must be installed without wrinkles or fish¬ mouths. The base flashing should extend a minimum of 8 inches above the top surface of the waterproofing assembly (e.g., pavers, stair treads, etc.) and requires termination bars to secure the top of the base flashing in place. Some climates may require higher base flashing extension above the top surface to better resist drifting snow. Metal skirts, masonry, or other protec¬ tion may be necessary to cover base flashings in locations where exposed flashings are nondurable or undesirable. We specified uncured Neoprene base flashings at our project and the workers first attempted to adhere the base flashing with the membrane man¬ ufacturer’s recommended Neo¬ prene adhesive. We easily re¬ moved the base flashings adhered with Neoprene adhesive by hand. As an alternative, workers set the base flashings in hot-fluid-applied rubberized-asphalt, which result¬ ed in well-adhered base flashings that we could not remove by hand (Photo 11). We also secured the top of the Neoprene flashing in place with continuous hook strips that also fastened copper protec¬ tion plates over the Neoprene flashings. At our project, the integration of the hot-fiuid-applied rubber¬ ized-asphalt membrane with the self-adhered membrane applied to the below-grade wall at the bot¬ tom of the stairs was a significant challenge. Although the fluidapplied rubberized asphalt mem¬ brane and the asphalt in the self¬ adhered membrane are compati¬ ble, we had learned on previous projects that the polyethylene facer on the self-adhered mem¬ brane inhibits bond between the Proceedings of the RCI 24th International Convention Piteo and Terpeluk -161 hot rubber and the self-adhered sheet membrane. We worked with the membrane manufacturer and the contractor to extend the self-adhered membrane on the wall and approximately 6 inches onto the hori¬ zontal surface of the bottom stair tread. The contractor removed the polyethylene carrier sheet from the top surface of the self-adhered membrane with a torch and then applied the hot-applied rubberized asphalt over the self-adhered membrane {Photo 12). In doing so, we avoided the interference of the polyethylene layer with the bond between the hot-fluid-applied asphalt and the self-adhered membrane. Similar to base flashings, membrane penetrations, such as pipes and dowels, should be flashed prior to membrane <3. larly difficult to waterproof, given the small size of the dowel, possible close dowel spac¬ ing, and the high temperature of membrane during installation. Although many details at¬ tempt to flash dowels by simply coating them with hot rubber, we have found it practical to create a higher flashing height with uncured Neoprene sheet flashing set in hot-fluidapplied rubberized-asphalt. At our project, workers first installed a Neoprene target patch set in hot-applied rubberized asphalt, tightly fixed around the dowel with an “X”-shaped hole {Photo 13). Next, the workers wrapped the dowel with a Neoprene sleeve. The workers first attempted to secure the Neoprene sleeve Photo 13 (left) – Neoprene test patch with “X”-shaped cut tightly fit around a dowel and set in hot-fluid-applied asphalt water¬ proofing. Photo 12 (above) – Hot-fluid-applied asphalt water¬ proofing membrane lapped over self-adhered water¬ proofing membrane at the vertical foundation wall. Workers removed the polyethylene carrier sheet from the surface of the self-adhered membrane to prevent bond interference between the hot-fluid-applied asphalt and self-adhered membrane. installation and require carefully con¬ structed details to provide durable water¬ proofing performance. Dowels are particu- Photo 14 (below) – Neoprene sleeve flash¬ ing wrapped around dowel and secured with duct tape to prevent the membrane from unwrapping during placement of the hot-fluid-applied rubberized asphalt. Piteo and Terpeluk – 162 Proceedings of the RC1 24th International Convention £ DRAINAGE LAYER All membranes should include a membrane- level drainage layer to improve system drain¬ age. Drainage layers can range from an open space below a paver system to an engineered drainage Photo 15 – Placement of protection board over reinforced hot-fluid-applied rubberized-asphalt membrane. stair risers and treads. The 14-in thick pro¬ tection sheet is too stiff to bend and conform to the shape of the stairs (Photo 16}. To solve the problem, the contractor cut the protec¬ tion sheets into smaller and more manage¬ able strips that covered several inches of the horizontal tread near the nose of the stair, the vertical riser below the tread, and the subsequent tread below the riser (Photo 17). We found that these smaller protection sheet strips were less susceptible to bowing at the vertical risers. We also made sure to shingle lap seams in the protection sheets and main¬ tain slope to drain at each stair tread. Photo 16 – Uncut pro¬ tection board lapped over entire portion of stairs. Note that the protection board bulges at stair risers and does not conform to the shape of the stairs. Photo 17 – Protection board cut into smaller and more manageable pieces that lap several inches onto each tread near the nose of the stair, over the vertical riser, and over the majority of the tread below the riser. Note that the protection board conforms to the shape of the stairs. A protection sheet is required by most manu¬ facturers and is placed over and bonded to the membrane while it is still aggres¬ sively tacky to complete the membrane appli¬ cation (Photo 15). Seams in the protection layer are lapped to provide continu¬ ity. We found that workers had difficulty apply¬ ing the protection layer at some details, such as to the dowel with the manufacturers rec¬ ommended adhesive prior to pouring hotapplied asphalt over the dowel. but the adhesive did not hold the sleeve together. We successfully secured the Neoprene wrap with tie wire and duct tape to prevent the membrane from unwrapping while workers installed the hot rubber at the dowels (Photo 14). Proceedings of the RCI 24th International Convention Piteo and Terpeluk – 163 Photo 18 – Continuous layer of drainage board that conforms to the shape of the stairs. systems above occupied space. Plaza assemblies with hot-fluidapplied rubberized-asphalt water¬ proofing membranes typically include insulation on top of the membrane in a protected mem¬ brane roof (PMR). Our project did not include insulation above the plaza deck assembly because the additional system thickness would unacceptably alter detail¬ ing at the entrance and the base of the portico columns. Relocation of insulation below the deck or omission of insulation altogether is often acceptable in small areas and on historic buildings. We were not involved with the fit-out of the interior space below the plaza but noted that the ceiling could be configured to include insulation below the membrane. Insulation installed below the board with integrally bonded geo¬ textile fabric to prevent fine parti¬ cles from clogging the drainage layer. A drainage layer should always be installed directly on top of the membrane protection layer to promote the flow of water at the membrane level. Although beyond the scope of this paper, some waterproofing systems may require multiple drainage layers for more reliable performance. As described earlier, the stair treads and risers are a difficult waterproofing detail. The sub¬ strate below stair treads must slope to drain water and include a drainage layer to provide space for water to flow below the stairs. The dimpled drainage layer installed at our project was flexible enough to conform to the nose and heel of the stairs and provide a continu¬ ous drainage plane {Photo 18). However, the drainage layer must also integrate with the water¬ proofing above and below the stairs to conduct water into the intended drainage plane and resist unsightly stains and efflo¬ rescence at poorly integrated or missing drainage layers (Photo 19). In addition to the stair drainage layer, we installed the limestone stair treads on top of alternating 6-in-wide mortar-setting beds, spaced at 12 inches on center (Photo 20). The openings between the mortar-setting beds promote drainage below the stairs. INSULATION Insulation, required by code for most buildings, improves the thermal efficiency of a building, helps to maintain occupant com¬ fort, and is often included in plaza waterproofing membrane is typi¬ cally protected from moisture and is primarily concerned with insu¬ lation value (R-value). Insulation above the membrane must con¬ sider numerous items in addition to R-value, including the antici¬ pated plaza traffic, overburden loads, long-term creep of the insulation, reduction of insulation value due to wet conditions, and separation between the insulation and membrane to prevent spot adhesion, which can damage the membrane if the insulation floats. All of these insulation issues are important, but none are spe¬ cific to hot-fluid-applied rub¬ berized-asphalt membranes and are beyond the scope of this paper. SURFACING AND BALLAST Hot-fluid-applied rubber¬ ized-asphalt waterproofing systems require surfacing (paving, soil, etc.) and, in most applications, ballast. Surfacing provides a fin¬ ished protective layer, while ballast provides weight to hold plaza components in place. Surfacing and ballast Photo 19 – Stain at stairs installed over hot-fluid-applied rubberizedasphalt waterproofing with no drainage layer at a waterproofing project. come in many shapes and Piteo and Terpeluk – 164 Proceedings of the RCI 24th International Convention sizes and may include stone, con¬ crete pavers, a cast-in-place con¬ crete slab, or growing media. The required surfacing or ballast depends on many factors, which may include wind resistance, buoyancy resistance, durability as a wearing surface, UV resis¬ tance, and appearance. A compre¬ hensive discussion of surfacing and ballast is beyond the scope of this paper; however, ANSI/SPRI RP-4, the Wind Design Standard for Ballasted Single-ply Roofing Systems, offers guidance for bal¬ last selection. Surfacing and ballast selec¬ tion should also consider success¬ ful systems installed in the same locale as the building. Two impor¬ tant considerations for surfacing and ballast installed over hotfluid- applied rubberized-asphalt membranes are: Photo 20 – Alternating mortar-setting beds and drainage space installed below limestone stair treads. Support: Some surfacings and ballasts rely on continu¬ ous support from the sub¬ strate (e.g., mortar-set pav¬ ers), and some ballasts rely on discrete points of support (e.g., pavers on pedestals). Continuously supported bal¬ lasts tend to evenly distribute loads through the membrane while discrete support points concentrate loads on the membrane. Concentrated loads can cause membrane squeeze out or damage and reduce durability. • Configuration: Surfacing and ballast should not include sharp edges that can penetrate and damage the waterproofing membrane. Systems made up of many small elements (i.e., stone) should include a protection layer (e.g., protection sheets) to separate the surfacing or ballast from the membrane. SUMMARY Hot-fluid-applied rubberizedasphalt membranes have a long track record of performance in waterproofing applications, but often face considerable challenges during construction, such as unanticipated existing conditions and unique details. While con¬ struction challenges are not uncommon, their exact nature is difficult if not impossible to pre¬ dict during design. Active con¬ struction administration, with fre¬ quent monitoring through site vis¬ its, along with a sophisticated quality control program orches¬ trated by a professional water¬ proofing contractor are critical to successfully address construction challenges in order to avoid condi¬ tions that can reduce the durabil¬ ity of the waterproofing system. Proceedings of the RCI 24th International Convention Piteo and Terpeluk – 1 65
