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Questions and Answers
Which characteristic of bitumen is necessary for creating a strong bond between plies in built-up roofing?
Which characteristic of bitumen is necessary for creating a strong bond between plies in built-up roofing?
What role do resins play in the composition of asphalt?
What role do resins play in the composition of asphalt?
Which of the following best describes the thermal properties of bitumens in built-up roofing?
Which of the following best describes the thermal properties of bitumens in built-up roofing?
What is the primary advantage of built-up roofing (BUR) compared to newer roofing technologies?
What is the primary advantage of built-up roofing (BUR) compared to newer roofing technologies?
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Which of the following statements is true regarding the flash point of asphalt?
Which of the following statements is true regarding the flash point of asphalt?
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What characteristic of Type III asphalt makes it suitable for steeper roofs?
What characteristic of Type III asphalt makes it suitable for steeper roofs?
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Which type of asphalt is most appropriate for roofs with a slope exceeding 2 inches per 12 inches?
Which type of asphalt is most appropriate for roofs with a slope exceeding 2 inches per 12 inches?
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What is the primary benefit of the cold flow property of coal tar?
What is the primary benefit of the cold flow property of coal tar?
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What does the Equiviscous Temperature (EVT) concept pertain to?
What does the Equiviscous Temperature (EVT) concept pertain to?
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Which of the following statements about the characteristics of roofing-grade asphalts is true?
Which of the following statements about the characteristics of roofing-grade asphalts is true?
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Study Notes
Built-Up Roofing
- BUR is the oldest and still popular low-slope roofing method
- BUR consists of layers of reinforcing felt sandwiched between bitumens
- Asphalt and coal tar are the bitumens of choice
- Bitumens are versatile waterproofing material
- Bitumens become more fluid with heat and solidify as they cool
- Correct application temperature is essential for creating a quality roof membrane
- High bitumen temperature is needed for the welding process
Properties of Bitumen
- Heating bitumen for a long time can reduce the softening point of asphalt and raise the softening point of coal-tar bitumen
- Bitumens can be kept at high temperatures for short periods of time without damage
- To achieve complete fusion and bonding of plies, bitumens need to be heated to high temperatures
Manufacturing Asphalt
- Three elements make up asphalt: saturants, asphaltenes, and resins
- Saturants are light oils that provide flexibility
- Asphaltenes provide body, rigidity, and strength
- Resins bond the saturants and asphaltenes to increase resilience
- The crude oil source and manufacturing processes impact the quality of the finished asphalt product
- Different crudes provide distinct characteristics
- California crudes have low saturants and flash points
- Flash point is the temperature at which light oils evaporate and ignite
- Higher flash point indicates less combustion
- Softer crude sources or blends with soft material are preferred for roofing applications
- Blending and blowing the crude-oil fluxes determine the characteristics of the finished asphalt
Asphalt Grades
- Type I (dead level): susceptible to flow at roof temperatures and has good adhesive and self-healing properties. Used up to ½ inch per 12 inches slope roofs
- Type II (flat): moderately susceptible to flow at roof temperatures. Used for slopes between ½ inch per 12 inches and 1½ inches per 12 inches
- Type III (steep): relatively nonsusceptible to flow at roof temperatures. Used for slopes between 1 and 3 inches per 12 inches
- Type IV (special steep): relatively nonsusceptible to flow at roof temperatures. Used for slopes between 2 and 6 inches per 12 inches
Equiviscous Temperature (EVT)
- The flow characteristic, or viscosity, of roofing bitumens at the point of application is important in BUR membrane construction
- EVT is defined as the temperature at which the viscosity of a bitumen is sufficient for proper adhesion, waterproofing, and application rate
Manufacturing Coal Tar
- Coal tar is a byproduct of coking bituminous coal during steel production
- Coal tar is resistant to aging, chemical breakdown, and moisture
- Coal tar is known for its resistance to ponded water
- Coal Tar's cold flow property allows for self-healing cracks and fissures.
- Three types of coal tar are used:
- Type I coal-tar pitch: used in BUR systems with coal-tar saturated felts.
- Type II coal-tar pitch: used in dampproofing and membrane waterproofing systems
- Type III coal-tar bitumen: used in BUR systems, has a higher softening point than Type I coal-tar pitch.
Coal Tar Types
- Type I and III are suitable for BUR construction, with Type III having less volatile components.
- EVT also applies to coal-tar products, but the recommended viscosity base is lower than asphalt.
Coal Tar Temperature Ranges
- Type I Coal-tar pitch, approximately 360°F, plus or minus 25°F
- Type III Coal-tar bitumen, approximately 375°F, plus or minus 25°F
Selecting Felts and Base Sheets
- Several materials are used as reinforcing sheets and base sheets in BUR construction:
- Saturated Roofing Felts: can be asphalt or coal-tar saturated. Organic felts are made from fiber of paper, wood, rags, or a combination.
- Asphalt Glass-Fiber Mat Sheet: glass-fiber mat impregnated and coated with asphalt. Available in perforated or unperforated forms.
- Venting Asphalt-Saturated and Coated Inorganic Sheets: heavy-gauge felt that vents specific roof conditions.
Saturated Roofing Felts:
- Organic felts are described by gauge, representing the weight per area e.g., 27-gauge = 27 pounds per 480 square feet.
- No. 15 asphalt-saturated organic felts: include perforated for two-, three-, or four-layer applications and unperforated for underlayment.
- No. 15 coal-tar saturated organic felts: ply marked for two-, three-, or four-ply applications, commonly used in waterproofing and coal-tar BUR specifications.
- Asphalt-impregnated glass-fiber felts: used in BUR membranes construction.
- Asphalt-impregnated glass-fiber felts (Type IV): heavier than Type III, with nearly twice the breaking strength.
Caps and Flashings
- Several caps and flashings are available for use in BUR applications:
- Wide-Selvage Asphalt Cap: asphalt-saturated felt with an asphalt-coated surface and colored mineral granules. Used for two-layer applications over a base ply.
- No. 90 Mineral-Surfaced Roll Material: with or without selvage, supplied with various ceramic-colored granule surfacings, used as organic roll roofing and in flashing applications.
- No. 50 Smooth-Surfaced Material: roll asphalt, used as a heavy-duty base sheet, temporary roofs, and flashing applications.
- No. 60 Smooth-Surfaced Material: organic felt saturated with mineral-stabilized asphalt compound, surfaced with talc or mica, used for inexpensive roll roofing.
- Inorganic Cap Sheet: heavy-weight inorganic felt saturated and coated with asphalt, surfaced with colored mineral granules, used as a top surface, for flashings, granular-surfaced lightweight roof system constructions, and for decorative purposes.
- Reinforced Bituminous Flashing: heavy saturated felt, reinforced with glass fiber, surfaced with fine mineral matter.
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Description
Explore the principles of Built-Up Roofing (BUR), a traditional low-slope roofing method that involves layers of bitumen and reinforcing felt. Understand the key properties of bitumen, including temperature requirements and the essential components of asphalt in roofing applications. This quiz delves into the applications and technical aspects vital for roofing professionals.
