BY STEVEN REINSTADTLER
John F. Kennedy said, when addressing the 87th Congress in 1962, “The time to repair the roof is when the sun is shining.” That statement’s fiscal and literal meaning is not lost on the contemporary financial decision of whether to tear off a leaking roof and reroof it or to make repairs to the cause of the leaking areas. In either case, there are significant monetary, operational, and sustainability implications that affect the final decision. That is why, in this election year, facility decision makers must consider their roof coating options like candidates on a ballot – weighing the attributes of each against the other and deciding which best fits their needs.
Like the early days of a presidential campaign, the roof coating field is crowded with choices. Some choices you may never had heard of, others have demonstrated track records. Some have weaker backgrounds while others have long-term desirable characteristics. Over time the pack thins out and those candidates with the correct price-to-performance record remain in the running. Here we will focus on a group of candidates with a demonstrated record of proven performance – high durability roof coatings based on polyurethane technology. We will review the background and traits of several types of polyurethane roof coatings and describe an end-use project where the facility owner voted to use a particular roof coating system – including why the owner elected to do so.
THE POLYURETHANE ROOF COATING PLATFORM
During the late 1930s, Otto Bayer pioneered the discovery of polyurethanes, a technology in broad use today. Due to their ability to vary physical properties, polyurethanes are widely used in a variety of materials. These include foams for building insulation such as spray polyurethane foam (SPF) and polyiso board, adhesives for construction and specialty applications, textile fibers for clothing and consumer products,thermoplastics for automotive and general industrial parts, and coatings for a variety of substrates and applications. Polyurethanes have shown their versatility in a wide range of applications in building, infrastructure, and architectural markets, which makes them a front runner in the roof coatings race.
Roof coatings based on polyurethanes are durable because they provide a unique combination of flexibility and weatherability, as well as chemical, abrasion, and impact resistance. These coatings can also provide reduced VOC emissions, superior coating thickness and improved hang on vertical surfaces. A well-formulated roof coating provides the advantage of fewer required coats, reducing cost per application by reducing and simplifying labor for the contractor. At the same time,the higher level of performance can require less surface preparation and provide the ability to self-prime. Furthermore, polyurethane roof coatings have faster curing times, allowing for increased productivity and driving their widespread use in the roofing market.
Polyurethane roof coatings come in both single component (moisture cure) and plural component (chemical cure) systems with different speeds of reactivity. The solids content of polyurethane coatings is typically moderate-to-high. High solids coatings have little to no solvent in their composition and were first introduced to comply with increasingly stringent VOC regulations. Due to this increased solids content and lack of solvent, these coatings needed to be formulated differently than those coatings with lower solids. The removal of solvents, which are used in traditional coatings to compensate for viscosity, flow and curing, requires the new coatings to have different characteristics and methods of handling. Just as a candidate might surround him or herself with a group of team members such as a campaign manager, fundraising director, finance manager, and grassroots coordinator, a polyurethane roof coating formulator does not rely solely on a successful resin. Instead, the formulator enlists supporters such as catalysts, flow and leveling agents, solvents, and pigments in order to formulate an electable commercial roof coating. Additionally, raw material suppliers have developed lower viscosity resins and methods for coating formulators to employ to allow for user-friendly roof coating systems.
TOP PICKS IN THE POLLS
For popular roof coatings, aromatic vs. aliphatic, run a tight race. Polyurethane roof coatings can be grouped into two broad categories, aromatic or aliphatic. Either type can be a single or two-component system. Aromatics have moderate-to-high tensile strength and elongation with medium-to-high solids. They are typically used as a base coat (primer), although some formulations can be used for top coats. If the backbone is not carefully selected, the color and properties can drift away from the original desired traits.
An aliphatic coating has similar properties as aromatic coatings but at a higher price point and their solids content is generally not as high. Aliphatics are usually touted for their light stability and therefore exhibit excellent long-term UV resistance, and also have excellent color retention, staying true to message. These attributes, along with the coatings’ inherent dirt resistance, allow the coatings to have excellent initial and long-term solar reflectance. Because of the superior properties, building owner and contractor constituents often vote for polyurethane roof coatings.
ONE COMPONENT VS. TWO COMPONENT: TOO CLOSE TO CALL
One-component, moisture-cure roof coatings are one of the most common polyurethane-based liquid applied roofing systems. They are popular since they have a good price and performance balance versus other liquid coating technologies. For the roofing contractor, they are easier to apply than two-component polyurethane systems since most of the reaction has already taken place in the supplier’s reaction vessels by combining the two polyurethane components. A range of physical properties such as elongation and hardness can be obtained by varying the resin selection. Single component polyurethanes cure by using humidity in the air and offer longer working life. They have moderate-to-high solids, can be aromatic or aliphatic, and are also often used as a vapor retarder or breathable membrane depending on the specific formulation. These one-component coatings can be applied by the roofing contractor in the field using conventional methods such as roller, squeegee, or single-component sprayer rather than specialized plural-component spray equipment.
Aliphatic one-component polyurethane roof coatings are a relatively new class of coatings compared to other technologies and represent a significant step up in long-term durability, weatherability, and waterproofing. The aliphatic polyurethane technology is similar to the exterior clearcoats used in the automotive industry for excellent long-term color and gloss retention as well as UV and weather resistance. While higher cost than aromatic-based coatings, they offer a higher level of in-service performance and longer service life.
Two-component roof coatings have a medium-to-fast cure time, limiting the window of opportunity when installing. However, the faster cure time provides a faster finish, which limits defects due to rain or environmental contaminants such as leaves or insects. The two components are metered out at the correct mix ratio at the job site through a spray gun by a plural component spray rig and react with each other and then cure. The cure is standard-to-fast and therefore requires care in mixing due to a limited pot life. Some coatings may only be sprayed through two-component equipment. Two component polyurethanes have high tensile strength and resist mechanical damage. They can be either aromatic or aliphatic.
THE RESULTS ARE IN ON THIS JOB
The U.S. Army Base Fort Carson in Colorado Springs is home to the 4th Infantry Division, the 10th Special Forces Group, as well as several other battalions and regiments. It was established in 1942 following Japan’s attack on Pearl Harbor. The Division’s mission is “To train, deploy and sustain brigade units of action; on order, conduct decisive full-spectrum combat operations in order to accomplish Combatant Commander Objectives.” Approximately 26,000 active duty personnel are stationed at the base. Therefore, it is important to have as few disruptions to the schedule and training of the personnel as possible. For this reason, when base facility maintenance personnel were faced with an aging and leaking roof on several of the platoon barracks, they needed to consider their immediate as well as long-term needs. U.S. Army personnel reached out to the front runner in polyurethane roof coating technologies, NEOGARD®, a Division of Hempel (USA), Inc., for a coating solution.
The existing building roof system consisted of a built up roof (BUR) and gravel that was out of warranty and past its useful service life. Since this area of the country receives significant hail, snow, and storms that can produce 100 MPH winds, the decision was made to upgrade the existing roof to a system composed of SPF and a high performance polyurethane roof coating. In addition, the owner wanted all upgrades and remodels to meet LEED standards.
The BUR roof was mostly intact and since there wasn’t any saturated insulation in the existing system, the existing roof was not torn off. From an environmental standpoint, this limited the impact of putting the old BUR and insulation in a landfill. The roof gravel was removed and recycled for other projects on the base as well. Next, the perimeter metal and nailer boards were replaced to enhance the wind uplift rating on the roof. Then, a three inch polyiso board was mechanically fastened with an I-90 wind uplift pattern followed by three pound closed cell spray foam, applied at a thickness of 2 inches with plural component spray equipment. This insulation board and spray applied polyurethane foam roof gave them an additional insulation value of R-15.
The coating system that was selected to protect the roof from elemental attacks was NEOGARD®’s Permathane™ II BIO, a single-component, aromatic polyurethane roof coating applied in two layers. First, 70620 was applied as a basecoat at 16 wet mils followed by a white top coat of 70611 at 16 wet mils with a broadcast of white granules at 35 pounds per square foot to maximize the reflectance of the roof. Both layers were applied using single-component, airless proportioners, which deliver a consistent application at a high coverage rate. The film thickness of each coat was confirmed using an optical comparator throughout the job site to verify the integrity of the coating application. The completed roof coating system provided the owner with a roof that met Energy Star, LEED emissivity qualifications and FM 4470 SH Class I hail rating. Additionally, the NEOGARD® Permathane™ II BIO line is a biobased polyurethane that is registered with the USDA BioPreferred Procurement program.
This winning combination of SPF and single-component coatings delivered on the campaign promise of easy application for the contractor, allowing the site team to meet the project’s time constraints. At the same time, the roof coating system’s greater tensile and impact strength provided excellent weather resistance and durability for this demanding locale. The election results are in and whether you are red or blue, it was a victory for everyone involved.
Which may have you pondering, “Ask not what your roof coating can do for you; ask what you can do to select the correct roof coating.”
NEOGARD® is a registered trademark of HEMPEL A/S CORP.™