The polyurethane foam is applied in a single step. Both parts of the adhesive are ready to use from the container – no mixing required – and are applied simultaneously in a 1:1 ratio through a static mix tip. It is applied in continuous ribbons or beads spaced 4, 6 or 12 inches apart, depending on the project and code requirements. There is no overspray, and it cures in minutes.
Helix Low-Rise Adhesive contains no volatile organic compounds (VOCs), chlorofluorocarbons (CFCs) or hydro chlorofluorocarbons (HCFCs).
It does not require mechanical fasteners, maintaining a puncture-free vapor retarder, preventing thermal bridging and protecting the structural integrity of the roof deck.
The bond created by Helix Low-Rise Adhesive provides wind uplift resistance, allowing it to be used on buildings in higher wind zones. In addition, it provides hail resistance when used as an adhesive for fleece-backed membranes.
Helix Low-Rise Adhesive comes in cartridge twin-pack tubes or two-tank sets. Both include one container of each of the adhesive’s two components – Part A and Part B. Cartridge twin-packs cover approximately 200-600 square feet of roof and tank sets cover approximately 1,000-3,000 square feet of roof, depending on bead spacing.
The cartridges fit most dispensing guns currently available on the market. Tank sets come with a Helix Gun Assembly (25-foot dual-hose with attached spray gun), petroleum packet, wrench, and 10 Tank Static Mix Tips. Contractors need not purchase specialty pumps or spray rigs. No external power source is required to run application equipment.
The primary function of a well-built and well-designed roofing system is to prevent water from moving through into the building below it. Yet, as the Rosemont, Ill.-based National Roofing Contractors Association has observed, an increasing number of “good roofs” installed on concrete roof decks have failed in recent years. Blistering, de-bonding and substrate buckling have occurred with no reports of water leakage. Upon investigation, the roofing materials and substrates are found to be wet and deteriorated.Why is this? One potential cause is trapped moisture; there are numerous potential sources of trapped moisture in a structure. Let’s examine the moisture source embedded within the concrete roof deck.
WHY DOES THIS MOISTURE BECOME TRAPPED?
It often starts with the schedule. In construction, time is money, and faster completion means lower cost to the general contractor and owner. Many construction schedules include the installation of the roof on the critical path because the interior building components and finishes cannot be completed until the roof has been installed. Therefore, to keep the project on schedule, roofers are pressured to install the roof soon after the roof deck has been poured. Adding to the pressure are contracts written so the general contractor receives a mile- stone payment once the roof has been installed and the building has been topped out.
Historically, roofers wait a minimum of 28 days after the roof deck is poured before starting to install a new roof. This is the concrete industry’s standard time for curing the concrete before testing and evaluating the concrete’s compressive strength. Twenty-eight days has no relation to the dryness of a concrete slab. Regardless, after 28 days the roofer may come under pres- sure from the general contractor to install the roof membrane. The concrete slab’s surface may pass the historic “hot asphalt” or the ASTM D4263 Standard “plastic sheet” test, but the apparently dry surface can be deceptive. Curing is not the same as drying, and significant amounts of water remain within a 28-day-old concrete deck. Depending on the ambient conditions, slab thickness and mixture proportions, the interior of the slab will likely have a relative humidity (RH) well over 90 percent at 28 days.
FROM WHERE DOES THE WATER COME?
Upon placing the concrete slab, the batch water goes to several uses. Portland cement reacts with water through the hydration process, creating the glue that holds concrete together. The remaining water held in capillary pores can be lost through evaporation, but evaporation is a slow, diffusion-based process. The diffusion rate of concrete is governed by the size and volume of capillary pores which, in turn, are controlled by the water/cement (w/cm) ratio. The total volume of water that will be lost is controlled by the degree of hydration, which is primarily related to curing and w/cm.
A 4-inch-thick concrete slab releases about 1 quart of water for each square foot of surface area. If a roof membrane is installed before this water escapes the slab, it can become trapped and collect beneath the roof system. The water does not damage the concrete, but it can migrate into the roofing system—and that’s when problems begin to occur. For instance, moisture that moves into the roofing system can:
- Reduce thermal performance of the insulation.
- Cause the insulation, cover board, adhesive or fasteners to lose strength, making the roofing system susceptible to uplift or damage from wind, hail or even foot traffic.
- Lead to dimensional changes in the substrate, causing buckling and eventually damaging the roof membrane.
- Allow mold growth.
A number of factors compound the problem. In buildings where a metal deck is installed, moisture cannot exit the slab through its bottom surface. Instead, the moisture is forced to exit the slab by moving upward. Eliminating one drying surface almost doubles the length of drying time of a concrete slab. The small slots cut in ventilated metal decking have little effect on reducing this drying time.
Ambient conditions also affect the drying rate of a concrete slab since it readily absorbs and retains moisture. Additional moisture may enter an unprotected roof slab from snow cover, rain or dew. Even overcast days will slow the rate of drying.
A MODERN-DAY PROBLEM
Before the introduction of today’s low-VOC roofing materials, historic roof systems didn’t experience as many of these moisture issues. Typically, they were in- stalled onto concrete decks on a continuous layer of hot asphalt adhesive that bonded the insulation to the deck. This low-permeable adhesive acted as a vapor retarder and limited the rate of moisture migrating from the concrete into the roofing assembly. As a result, historic roof systems were somewhat isolated from moisture coming from the concrete slab.
Many of today’s single-ply roof membranes are not installed with a vapor retarder. Moisture is able to migrate from the concrete slab into the roof materials. Modern insulation boards are often faced with moisture-sensitive paper facers and adhered to substrates with moisture-sensitive adhesives. These moisture-sensitive paper facers and adhesives are causing many of the problems.
Rene Dupuis of Middleton, Wis.- based Structural Research Inc. recently presented a paper to the Chicago Roofing Contractors Association on the subject. Some of his findings include the following:
- Due to air-quality requirements, government regulations curtailed the use of solvent-based adhesives because they are high in VOCs. Consequently, manufacturers changed to water-based adhesives because they are lower in VOCs, have low odor, are easy to apply and pro- vide more coverage.
- There can be several drawbacks to water-based bonding adhesives. One is that they may be moisture sensitive. Moisture and alkaline salts migrating into roof systems from concrete decks can trigger a negative reaction with some water-based adhesives. This reaction can cause the adhesives to revert to a liquid, or it may alter or delay the curing of some foam-based adhesives. Some adhesive manufacturers have recognized these problems and have be- gun reformulating their adhesives to address these drawbacks.
- Negative reactions also occur when moisture-sensitive paper facers come into contact with moisture. This reaction typically results in decay, mold growth and loss of cohesive strength. Moisture in the roof system may also cause gypsum and wood-fiber-based cover boards to lose cohesive strength.
Dupuis noted moisture from any source can compromise adhered roof systems with wind uplift when attached to paper insulation or gypsum board. He also said facer research clearly shows paper facers suffer loss of strength as moisture content increases.
PHOTOS: Wagner Meters
The start of a new school year is always an exciting time. As I see my friends post photos on Facebook of their kids’ first days of school, I am reminded of the excitement I felt way back when. I loved wearing a new outfit, seeing friends I hadn’t seen in awhile and anticipating all the fun—and learning—in the year ahead. In a way, I get to recreate those feelings each time I put together a new issue of Roofing. I’m continually learning about the industry and this issue is no different.
For example, in “From the Hutchinson Files”, Thomas W. Hutchinson, AIA, FRCI, RRC, CSI, RRP, principal of Hutchinson Design Group, Barrington, Ill., and a Roofing editorial advisor, explains the virtues of cover boards. As he points out in his article, the use of cover boards can now be considered a good roofing practice.
Meanwhile, Jared O. Blum, president of the Polyisocyanurate Insulation Manufacturers Association, Bethesda, Md., explains a new white paper about polyisocyanurate insulation R-values in “Cool Roofing”. He states the R-value of polyiso roof insulation is reduced at some point at lower temperatures, but within any reasonable temperature range associated with typical building operating conditions in almost any climate in North America the difference appears to be very small.
In addition, we here at Roofing like to learn and try new things. As a result, this issue is interactive! Please download the free Layar Augmented Reality app, which was designed to bring print to life. Then hover over page 45 in the print edition with your smartphone or tablet to view a video about Virginia Polytechnic Institute and State University’s Indoor Practice Facility in Blacksburg, Va., which features almost 1,000 squares of 238-foot-long, curved, standing-seam metal panels. We’re really excited about this new capability and would love to know what you think.
Continuing on our roof system component analysis—after discussion of the roof deck, substrate board, vapor retarders and insulation—we now have worked our way up to the cover board. For the purpose of this discussion, the cover board is defined as the board placed upon the insulation as the final substrate to which the roof cover will be placed.
The purpose of the cover board is multifaceted; it can include:
Insulation Protection: Placed to protect the thermal layer from the often deleterious effects of repeated foot traffic, which can result in insulation crushing, loss of roof-cover adhesive, inability to resist wind uplift and mechanical- fastener puncture through the membrane.
Enhanced Roof-cover Adhesion: Cover boards can enhance the bond between the roof cover to the substrate.
Enhanced Resistance to Wind Uplift: Cover boards and their ability to enhance the bond of the roof cover to the underlying substrate can result in an increased wind-uplift rating above and beyond that which can be provided with organic-faced insulations. They reduce the possible effects of facer-sheet delamination.
Enhanced Fire Resistance: Many cover boards will enhance the fire resistance of the assembly.
Hail Protection: Numerous studies show the value of cover boards in enhancing a roof cover’s ability to resist damage by hail.
Provides Separation: A cover board provides separation between a roof cover and insulation that may not be compatible or the attachment adhesive of the roof membrane is not compatible with the insulation.
Reduces Thermal Shorts (Energy Loss): Thermal insulation is often attached to the roof deck with mechanical fasteners, which results in conductive heat loss, up to 7 percent according to the Rosemont, Ill.-based National Roofing Contractors Association. This is a large value when some roof covers, which utilize mechanical attachment, purport to provide energy savings. Furthermore, when only one layer of insulation is used (a cardinal sin in my opinion) an additional 7 to 8 percent energy loss can occur. Placing a cover board above mechanically attached insulation and/or a single layer of insulation will enhance the energy performance of the roof system.
Enhanced Roof-system Performance: I firmly believe the use of a roof cover board in a roof system improves the overall performance of the roof system and increases the probability of the roof attaining a long-term service life, which is the essence of sustainability. NRCA agrees; the organization recommends the use of cover boards in all low-slope assemblies.