Hot Mop Roofing Vs. Cold Roofing Process

Built-up Roofing

• Roofing with a shallow pitch and a built-up roof consists of several layers. The roofing deck provides the structural frame underlying the roof. Roof decks made from wooden boards, plywood, steel or concrete are all compatible with built-up roofing. Sheets of asphalt-coated roofing felt are applied over the entire roofing deck with layers of adhesive applied between each layer to form a solid barrier against the penetration of water. A final layer made of gravel, ceramics or cap sheeting is applied over the roofing felt to protect it from UV damage.

Hot Mopping

• Hot mop roofing is a traditional form of built-up roofing that uses layers of hot bitumen to seal each layer of roofing felt. There are four basic types of bitumen that soften at different temperatures. Type 1 bitumen softens at relatively low temperatures and is most suitable for flat roofing. Types 2 through 4 require increasingly higher temperatures to soften and are used for roofs with steeper pitches. The bitumen is heated in a vat on the ground and carried or pumped to the roof where it is applied using mops before it can cool. Hot mopping is a labor-intensive process because each roof typically requires three to four applications of bitumen.

Cold Roofing

• Cold roofing replaces hot bitumen with a cold process bitumen. This material uses a solvent-based mastic adhesive to create a water-resistant bond between each layer of roofing felt. The main advantage of cold roofing materials is that there is no risk of injury from burns or damage to the structure from accidental fire.

Considerations

• When hot bitumen is heated, it releases noxious fumes that are hazardous to workers. Hot mopped roofs require additional pumping equipment to transport the heated roofing material from the ground onto the roof. If a pump is not used, you must manually carry the hot bitumen to the roof in buckets. If the bitumen cools before it is applied, it can negatively affect the quality of the finished roof.