It’s summertime, which means you may be seeing more asphalt being applied to commercial roofing systems than any other time of the year, especially if you live in cold-weather climates. If you’ll be applying asphalt to a roof this summer, keep in mind that the coverage rate of hot asphalt as an interply adhesive is very important.
This is because the pro per coverage rate of asphalt ensures adequate adhesion of the plies to the substrate. The NRCA states that the recommended application temperature range for hot asphalt is what’s called the Equiviscous Temperature (EVT), which roughly equates to a coverage rate of 25 lbs. per square per ply sheet. As you install the modified roll into the hot asphalt, be sure to push a puddle of asphalt – this ensures complete coverage and eliminates trapped air that can cause blisters.
The EVT is important for hot applied systems because it’s the temperature at which hot asphalt attains the proper viscosity for application, which ensures the proper coverage rate and proper temperature to create a monolithic roofing system. When the asphalt is hot enough, it will melt the backside of the modified sheet and provide a monolithic roof system.
Without ensuring that the asphalt is in the proper EVT range, you could end up with asphalt that is too cold. This results in too much asphalt, which can mean:
- Slippage of plies
- Slumpage of asphalt
- Increased stress on plies
- Decreased stability
- Delamination of ply sheets
- Decreased positive drainage
- Decreased flexibility and strength
You could also end up with asphalt that is too hot, which yields an insufficient coverage and can mean:
- Inadequate adhesion
- Decreased waterproofing
When in the field, the most accurate method for testing EVT of asphalt is a thermal temperature gun.