Solvent-based roof coatings are your best options for restoring built up and modified bitumen since they are designed to stand up to ponding water better than acrylic coatings.
Asphalt roofing systems are low-slope roofs that consist of multiple layers of asphalt or bitumen and reinforcing felt. Asphalt roofing systems for commercial, industrial and institutional buildings are Built-Up Roofing (BUR) and Modified Bitumen Systems (MBS).
Built-up Roofing used on flat or low-sloped roofs and consists of multiple layers of bitumen and ply sheets. Components of a BUR system include the roof deck, a vapor retarder, insulation, membrane and surfacing material. The components are assembled at the job site to actually form the built-up roof. At the heart of this roofing system is the roofing membrane, which consists of roofing bitumen and multiple reinforcing plies of roofing felt.
Roofing bitumen is the primary adhesion/waterproofing agent used between roofing plies. Bitumen arrives at the job site in solid form, but is heated and applied as a liquid. Roofing bitumens may be either a product of petroleum refining (asphalts) or a product of the coal-cooking process (coal tar pitch).
Multiple reinforcing “plies” are asphalt-coated roofing sheets or felts installed in three or more layers to strengthen and stabilize the BUR membrane. These multiple reinforcing felts also make the membrane more pliable and resilient, protect the bitumen from water degradation, and serve as a fire-retarding element in the membrane system.
BUR roofing membranes can be protected from solar radiation by embedding gravel in the bitumen, applying a surface coating or applying a granular-surfaced “cap” sheet. Light-colored surfacing materials can be used to reflect heat from the building. In addition, surfacing agents can provide additional fire protection.
A lot of old buildings with low slope or flat roofs are topped with smooth built-up roofing ballasted with rock or gravel, to hold down the roofing material. Built-Up Roofs with gravel surfacing are also known as Tar and Gravel roofs. Typical lifespan of a built-up roof is 10 to 20 years.
Ballasted Built-Up Roofs are sometimes called Tar and Gravel roofs when coal tar is used instead of asphalt.
Typical lifespan of a built-up roof is 10 to 20 years depending on weather conditions.
The service life of a built-up roof can be extended by another 10 years with the application of an elastomeric roof coating. Elastomeric coatings have become a very popular alternative to roof replacement. They are usually white and can reflect up to 90% of the heat from the sun.