From the Deck Up: Asphalt
In recent years, concern about the use of asphalt in roofing applications has been discussed and debated. The fact remains that BUR systems using asphalt have the longest performance record of any roofing system and roofing crews have the most experience in BUR application. BUR is a durable system that repairs well and is cost effective to apply. Because of its longevity, maintenance crews understand the system and are able to make minor repairs and modifications. In addition, the newer modified-bitumen systems, which also can utilize mopping asphalt for their application, are proving to be excellent performers. With the new technology available to reduce asphalt fumes and the ability to cold apply asphalt, many of the concerns are eliminated.
Is asphalt as good today as in the past?Over the years crude sources have changed. More oil is going into gasoline and less is left over as a crude source for asphalt. With improved processing and blending of various crude sources, asphalt today can have as good or better consistency than in the past. With today’s improved testing this consistency can be validated and controlled.
Is coking in the kettle a problem?Coking or overheating of asphalt in the kettle can be a problem. Control of the kettle temperature is critical and accurate thermometers or heat-sensing devices must be used. Today’s roofing kettles have better controls than those of the past did.
Can asphalt be degraded?Asphalt is a very durable product and holds up well under many adverse conditions. Degradation can take place in the kettle and on the roof unless attention is paid to detail. Asphalt typically is refined at about 500F. Prolonged exposure, usually four hours or more at temperatures in excess of 500F, could change its characteristics. If the lid of the kettle is up, the light ends could be driven off making the asphalt harder. If the lid is down, the light ends can condense on the cooler lid and drop back into the kettle producing softer asphalt. Of course, four hours at the elevated temperature without adding or pumping out asphalt is not likely to occur on many jobs. Degradation also takes place on the roof from exposure to ultraviolet rays. The types of surfacing used with asphaltic systems can retard this.
Has adhering to EVT guidelines helped?EVT, or Equivicous Temperature, has provided the industry with an accurate guideline to determine the proper amount of interply mopping asphalt by heating the asphalt to the correct temperature.
A keg of asphalt comes from the refinery with the EVT temperature printed on the label. The kettle is heated so that the asphalt is controlled to the EVT temperature + 25 F at the point of application. The operator also needs to take into consideration the ambient temperature, wind conditions and type of surface to which the asphalt is being applied.
What can be done to reduce asphalt fume on the job?Even though there are no restrictions on the use of asphalt, there are certain applications where fume and odor are undesirable. For example, recently the five-star Broadmoor Hotel in Colorado Springs was reroofed while the hotel remained in operation. In this case, the ownership of the hotel did not want hot asphalt used on the project.
However, fume recovery systems have been introduced to allow the use of BUR, in many cases filtering as much as 99 percent of the fume and odor at the kettle and lugger. One system eliminates odor, fume and particulates emitted at the kettle by using a fan to draw the fume and particulates through a hose to separate devices. Here the mixture passes through a thermal converter where it is mixed with fresh air and superheated to eliminate 99 percent of the odor and visible fume. As filters are not used in this method, no additional waste needs to be disposed.
A second method utilizes a fume recovery system that collects and filters the fume to nearly undetectable levels. The system is mobile and uses five different filtration modules, each designed to remove a specific type of airborne pollutant. With this system the filters must be replaced and disposed. Of course, the odor at the mop bucket (which is negligible) can’t be eliminated by either method. In addition these filtering systems do add additional cost to the job.
A third method uses low-fuming asphalt that minimizes fumes. When used with filter systems, overall costs are reduced since the filters last longer before they need to be replaced. Another plus with this method is the packaging, which stacks neatly at the job site and can be divided into two smaller, easier-to-handle pieces. When heated the packaging melts and floats to the surface, creating a skim layer, trapping the fume and odor inside the kettle. Energy is conserved as the skim layer keeps a portion of the heat inside as well.
Another method uses “cold asphalt” systems instead of hot asphalt. With this system, asphalt is brought to the job site suspended in a solvent to make it fluid and is either squeegeed and/or spray applied. As the solvent evaporates, the reinforcing sheets adhere to each other forming the completed membrane.