Plies may be adhered to each other using one or more of a variety of bituminous materials;
About Bitumens:
Bitumens are engineered asphaltic materials produced by the distillation of crude oil during the petroleum refining process. They are non-volatile (won’t boil or rapidly evaporate crucial chemical components) at ambient (indoor/outdoor) temperatures. At the refinery, raw asphalt- called “flux”- is heated to about 500°F.
In a process called “air entrainment”, air is blown through the liquid mix. The amount of time entrainment takes place produces different properties in the asphalt, such as viscosity (flow rate) and hardness. Proper viscosity and temperature during application are crucial and are specific to different types of project conditions and for effective long-term performance.
Polymer-modified bitumens were developed in Europe in the 1960s and have been used in North America since about 1975. They generally fall into two categories:
1. Atactic polypropylene (APP)-modified gives bitumen plasticized properties.
2. Styrene butadiene styrene (SBS)-modified gives bitumen rubberized properties.
The main bitumens used to adhere reinforcement plies together are:
1. Cold-applied asphalt adhesives;
2. Cold-applied polymer-modified asphalt adhesives;
3. Hot-applied asphalt; and
4. Hot-applied polymer-modified asphalt.
Polymers are molecular compounds added to materials to improve certain properties. In roofing materials they may:
• Improve durability;
• Improve flexibility;
• Improve low temperature performance
• Improve fire resistance;
• Improve resistance to ultraviolet (UV) damage from sunlight;
• Increase lifespan;
• Lower cost;
• Reduce weight,
1. Cold-applied asphalt adhesives
Cold-applied asphalt adhesives are thinned (“cut back”) with solvents, which allow them to be more easily spread between reinforcement plies. A variety of other additives are available. These may include stone powder or fibrous fillers, stabilizers, surfactants (compounds that lower surface tension to improve bonding), or viscosity modifiers.
Application may be by spray, brush, or squeegee, depending on product, manufacturer, and project/environmental considerations. Cold applied asphalt adhesives must be specified by designers and installed by applicators according to the manufacturer’s recommendations. Although inspectors may see the results of failures due to improper design or installation, they probably will not be able to accurately identify the cause, since a large variety of causes are possible, and identification lies outside the scope of the General Home Inspection.
2. Cold-applied polymer-modified asphalt adhesives
Polymer-modified asphalt adhesives use asphalt that has been enhanced by the addition of polymers to improve one or more performance characteristics.
Polymer-modified asphalt is available in a wide variety of formulas that may include from high to low percentages of solvents and asphalt.
Like with cold-applied asphalt adhesive, application of cold-applied polymer-modified asphalt adhesives may be by spray, brush, or squeegee. Cold-applied polymer-modified asphalt adhesives must be correctly specified by designers and installed by applicators according to the manufacturer’s recommendations. Again, inspectors are not responsible for identifying the causes of defective conditions they find.
Cold-applied polymer-modified asphalt adhesives may be used to bond plies and cap sheet, or as a top–pour application to be exposed to weather.
Polymers commonly used to modify cold-applied asphalt are:
• Styrene ethylene butadiene styrene (SEBS);
• Polyurethane; and
• Polyether.
3. Hot-applied asphalt
Using this method, asphalt is brought to the jobsite as solid rolls that are melted in a kettle. The liquid asphalt may be spread across plies using mops or with mechanical spreaders. Proper temperature is crucial to achieving a viscosity that will allow proper spreading and to providing an effective bond between plies.
4. Hot-applied polymer-modified asphalt
Hot-applied polymer-modified asphalt roof membrane systems are available that may be used to bond plies or as a top–pour application to be exposed to weather. These systems use conventional roofing asphalt that has been modified by styrene ethylene butadiene styrene (SEBS).
Benefits can include:
• Low temperature flexibility;
• UV resistance;
• Softening point;
• Flash (ignition) point;
• Penetration resistance; and
• Damage from thermal cycling.
• Fewer plies needed