Sky-facing masonry joints have been problematic since at least the time of ancient Egypt and the pyramids. Horizontal joints between masonry units such as brick, cast stone, concrete, terra cotta, marble, granite, etc. have allowed water entry into the most prestigious buildings, not just those built on a budget. Over time, many methods have been attempted to prevent this water entry; and in this article, we will present the current options that are installed, regardless of their viability as solutions to the weatherproofing of these difficult joints. Horizontal masonry joints can be small, as in the case of a shelf or water table (Figure 1); or extremely large, as when they are the defining elements of buildings’ cornices or entry pediments (Figure 2). Copings, windowsills, and other locations often contain horizontal masonry joints that need to be detailed to prevent water entry. The most common methods of detailing these joints today include: 1. Sealant 2. Pointing 3. Lead weathercap 4. Hot lead 5. Metal cladding (ledge and coping covers) 6. Liquid membranes A P R I L 2012 I N T E R FA C E • 5 Figure 1 – Small ledge above masonry ornamentation. Figure 2 – Large marble shelf at base of batten seam roof. SEALANT With advancements in sealant technology, we are seeing more and more horizontal masonry joints sealed with silicone and urethane sealants. Ease and speed of installation— making costs relatively low—along with warranty claims of 20+ years or more by sealant manufacturers, have spurred this type of detail. Rarely, however, do these types of joints last. In some in – stances, the use of self-leveling sealants is comically incorrect; however, they are still used (Figure 3). Just because a detail is popular does not make it functional or even economically viable. It is strongly recommended that life expectancy, cost of replacement, and consequential damages be considered before using sealant on horizontal ma – sonry joints other than for sidewalks on grade. POINTING The most common method of detailing sky-facing masonry joints is with mortar. This joint rarely has a weathertight life expectancy of more than a few years and, as such, should only be used when a continuous metal flashing is installed under the top course of masonry. Many polymeric flashing membranes have been tried in recent years; however, none has a track record as long and successful as metal. Before a polymeric membrane flashing is contemplated, the track record and cost of replacement should be considered. This type of detail is most common with copings when under-coping flashings are installed. Difficulty can arise when a single course of masonry is installed over the metal flashing because the metal acts as a bond breaker and can cause the coping to slide off the wall. To prevent this, three-way interlocking flashing or dowels are used to provide a positive bond of the coping to the parapet wall. Three-way interlocking flashing is metal that has been bent with corrugations that provide a physical interlock with the mortar above and below the metal to hold all components in place (Figure 4). When dowels are used, they serve as shear studs to pre- 6 • IN T E R FA C E A P R I L 2012 Figure 3 – Self-leveling sealant installed at joints in coping. Figure 4 – Three-way interlocking metal under-coping flashing. All seams and fastener heads soldered watertight. Figure 5A – Metal flashing with dowels. vent movement of the copings; however, each and every dowel must have a thimble flashing installed to prevent water entry at the dowel (Figures 5A and 5B). LEAD WEATHERCAPS Lead weathercaps, sometimes referred to as “T” caps, are a more effective method of sealing horizontal masonry joints than sealant but not as effective as when an under-coping metal flashing is installed. In some instances, such as repairs or retrofits, it is the only option, because lifting/resetting the masonry to install under-coping flashing is economically impractical or simply impossible no matter how much money is spent. A lead weathercap is solid lead in the shape of a “T” that is inserted into a horizontal masonry joint (Figure 6). Typical recommendations are to rake and repoint the joint, holding the new pointing mortar down approximately 2 in. from the surface How Many of these PROSOCO restoration projects do you recognize? Reverse the of time ravages Clean and conserve with Sure Klean® Restoration Cleaners, Weather Seal protective treatments and 60 years of PROSOCO expertise. A P R I L 2012 I N T E R FA C E • 7 Figure 5B – Close-up of thimbles at dowels. of the masonry. This offers some weatherproofing function but also provides a sound substrate to install new materials. The lead weathercap is dry-fitted prior to sealant installation; then, backer rod and sealant are installed over the new pointing to completely fill the joint. The weathercap is then “buttered” with sealant on the backside to prevent air pockets from forming and then inserted into the joint until it is flush with the horizontal surface. Masking tape on the face of the masonry keeps the joint looking clean when excess sealant is pushed from the joint (Figure 7). The type of sealant used can vary and must be selected so as to be compatible with the masonry. Some types of sealants will cause staining or dirt pick-up on particular types of masonry, so selection should be done with care. Urethane sealant is the most popular, although silicone and nonskinning butyl sealant have been used successfully. HOT LEAD A method no longer very common, but relatively effective, is what is often referred to as a leaded joint or hot lead. This type of joint is most commonly used to seal a horizontal reglet but has been used on joints between individual masonry units. To install a leaded joint, the mortar between masonry units must 8 • IN T E R FA C E A P R I L 2012 Figure 7 – Transition between up-facing head joint and weathering bed joint lead T caps. Figure 6 – Detail of lead cap at horizontal and vertical joints. be sound and solid to within one inch of the masonry surface. Lead wool is then pounded into the joint until it is full, and then the top surface is melted with an acetylene torch (Figure 8). This joint is similar to a lead and oakum joint in plumbing and is only used when joint movement is expected to be very small. METAL CLADDING In some instances, it is possible to change the horizontal masonry joints for metal joints. If a sky-facing masonry ledge can be clad with a metal that can be soldered, such as copper or lead-coated copper, the weatherproof life expectancy of the assembly can be in excess of 70 years. In these instances, the metal not only protects the joints between masonry units but can protect the masonry as well (Figures 9 and 10). The most common type of metal cladding is the installation of metal copings over masonry coping stones. There are many factory-manufactured copings that can be used to cover the horizontal masonry joints; however, almost any sheet-metal A P R I L 2012 I N T E R FA C E • 9 Figure 8 – Lead wool being pounded into place prior to heating. Figure 10 – Inclined marble pediment clad with lead-coated copper; all seams loose-locked. ENVIROSPEC INCORPORATED The PAVE-EL® Pedestal System • Transforms flat roofs into attractive, maintenancefree, landscaped paver stone terraces. • Elevates paver stones for perfect drainage. • Levels paver stones and ensures their uniform spacing for an ideal roof terrace surface. • Ideal for laying paver walkways in roof gardens. Turn your roof tops into beautiful, useful decks 716-689-8548 • www.envirospecinc.com Figure 9 – Flat marble ledge covered with leadcoated copper; connections made with “drive cleat” at seams. shop can fabricate a coping that provides a long-term weatherproof solution to a horizontal masonry joint. A well-designed metal coping assembly should require the repointing of the existing coping joints and/or the installation of a weather-resistive barrier under the metal copings. Simply installing metal copings over actively leaking coping stones often results in leaks within five or ten years due to incidental water passing the metal copings and following prior paths of water entry. With most coping systems coming in 8- or 10-ft. lengths, and masonry copings typically 4 or 5 ft., this immediately reduces the number of joints by at least half. To minimize the water passing joints in the metal copings, the joint configuration and size should be well planned. The use of welded miters; properly undersized, concealed splice plates of 12 in. or more with nonskinning butyl sealant; as well as urethane sealants go a long way to prevent water entry (Figure 11). Many other metal joint configurations are possible as can be viewed in the SMACNA Manual (standing seam, slip joint, exposed splice plate, etc.); however, most of these other types of joint configurations create a detail that is readily perceptible—something that is typically avoided if at all possible. LIQUID MEMBRANES With the advancement of chemical/ polymer technology, reinforced liquid membranes are becoming more prevalent in many construction details. The use of urethane and polymethylmethacrylate (PMMA) waterproofing systems at exposed horizontal masonry and joinery is a viable option and can solve many of the issues such as joint movement. The self-terminating characteristics of the materials allow 10 • I N T E R FA C E A P R I L 2012 The RCI Foundations – Supporting The Industry RCI Foundation – United States Web site: www.rcifoundation.org E-mail: foundation@rci-online.org Canada Web site: www.rcifoundation.ca mail: info@rcifoundation.ca Sup porting T e Fou Indust undations try s fou w Found undation@dation E-rcifounda rcifound RCI Foundation – Can ation.dation.nada Figure 11 – Coping assembly installed over repointed masonry copings. Note: Concealed splice plate is 12 in. overall, and butyl tape is installed only on horizontal portions. Figure 12 – In-progress detail of self-terminating liquid membrane terminating 1 in. back from coping edge. Membrane continues up cheek wall where the cut reglet detail is visible. them to be installed on horizontal masonry and stopped just shy of the exterior vertical face (Figure 12). As an added measure of precaution, liquid membranes can be let into a horizontal reglet that is cut into the masonry. As with all liquid membranes, surface preparation is critical to the performance of the material. Surface contamination and deterioration of the masonry being waterproofed often require aggressive substrate prep such as grinding or scarifying. Failure to properly prepare the substrate can result in catastrophic failure (Figures 13 and 14). A P R I L 2012 I N T E R FA C E • 1 1 Figure 13 – Mock-ups of different surface preparation for liquid membrane. Figure 14 – Substrate failure when deteriorated masonry is not prepared properly. New research is showing that the pursuit of green roofing may be coming at a price that is more than economical. In fact, a credit-by-credit analysis of projects pursuing certification through the U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED®) program shows that the safety of workers on these projects is at risk. In a study titled “Identification of Safety Risks for High-Performance Sustainable Construction Projects,” Matthew Hallowell, a professor at the University of Colorado at Boulder, identified 14 LEED® credentials that may create heightened risks to construction workers. Most notable risks include a perceived 41% higher risk associated with installing sustainable roofing; a perceived 37% increase in risk from installing PV panels for on-site renewable energy; a perceived 36% additional risk of cuts, abrasions, and lacerations from construction waste management; and a perceived 32% heightened risk of falls from installing skylights and atriums to meet the daylight and views credit. Below are some suggested tips to mitigate risks: — Mountainstates.construction.com CONCLUSION As of this writing, there is no panacea detail that solves all the problems of all horizontal masonry joints one might confront. These situations, similar to many others that are encountered on new and existing structures, are something that consultants must deal with and do their best on a caseby- case basis to provide their clients and their buildings with the most weathertight, longest-lasting, and economically viable details. Even in the best of situations, the solutions described above have limited life expectancy when compared to that of the base material (stone, marble, granite, etc.). As a result, this work must be considered a “maintenance item,” even if the work is expected to last 70-plus years. As a maintenance item, considerable thought should be given to the repair/replacement of the work at the end of its useful service life. Systems and details should be selected that are minimally altering and damaging to the base materials and allow multiple reinstallations without significant reworking of the masonry. The cutting of reglets and use of chemicals and adhesives must be well thought out—not only to prevent water entry but also to allow removal and reinstallation of future maintenance campaigns. 12 • I N T E R FA C E A P R I L 2012 Remo R. Capolino, RRC, PE, grew up in a family-owned specialty roofing and sheet metal contracting business and graduated from the University of Connecticut with a bachelor’s degree in civil engineering. After more than 15 years in contracting and leadership roles with the Association of General Contractors (AGC), Northeast Roofing Contractors Association (NERCA), and the National Roofing Contractors Association (NRCA), he turned to consulting, desiring to have an impact on a greater number of projects. Capolino has lent his expertise in copper, zinc, slate, and other specialty roofing assemblies on a number of internationally recognized projects. Remo R. Capolino, RRC, PE LEED Not Leading to Safety? LEED Credit: Heat Island Effect—Roof Identified risk: White roofing options can be heavier and more slippery than traditional black roofing material, which increases the risk for overexertion and falls. The bright material can interrupt line-of-sight and increase the risk of slips and falls during installation. Suggested mitigation: Tan or light gray membranes could be used to decrease reflectivity, or contractors could require tinted eyewear. Rubber walk pads could be provided for added traction, and contractors could purchase a greater number of smaller rolls to avoid overexertion from weight. LEED Credit: On-Site Renewable Energy Identified risk: Falls and overexertion are more likely from installing heavy PV panels, usually on the roof. Suggested mitigation: Designers could place PV panels closer to the ground or keep them as far from the edge of the roof as possible. Higher parapets and designed tie-off points may also lessen the risk of falling. LEED Credit: Daylight and Views: Daylight 75% of Spaces Identified risk: Large skylights, windows, or atriums increase time spent working near large, exposed openings at great heights. Suggested mitigation: Designers could create a courtyard to meet the requirements or minimize the depth of the building as an alternative to atriums and skylights. If these elements are included, additional precautions could be taken, such as blocking off areas below overhead work, using equipment such as man lifts and scissor lifts when possible, and using tie-offs and barriers near exposed openings.
