Modified Bitumen Silicone

Modified Bitumen Silicone is a Kool Coats coating system for modified bitumen roofs, built around a silicone finish. It belongs to the Modified Bitumen family of Kool Coats restoration systems and is listed for the USA market. The system is a layered assembly of an asphalt bleed-block primer, a silicone mastic for details and a high solids silicone roof coating.

The asphalt-based cap sheet is the substrate for this system. Asphalt oils can discolor a silicone finish, so the assembly begins with a primer made for asphalt bleed control. Granulated cap sheets have a rough surface, and the primer also fills the valleys between granules before the finish coat.

The system is one of the silicone roof coating assemblies in the Kool Coats range, alongside the acrylic system for the same substrate.

Three Kool Coats products make up the system. Each has a distinct job in the build.

• P-305 Asphalt and Bleed Block Primer goes on first. It is a water-based acrylic primer that controls asphalt bleed-through and smooths granulated surfaces before the silicone is applied.
• KF-460 KoolFlex Silicone Mastic treats details. It is a high solids, moisture cure, 100% silicone mastic for cracks, breaks, tears and holes.
• KF-600 KoolFlex High Solids Silicone is the field coating. It is a single component, moisture cure, elastomeric 100% silicone roof coating.

P-305 fills surface voids on granulated modified bitumen, which helps the silicone coating build to the required mil thickness more efficiently. It is specified for warranty silicone systems over asphalt-based substrates.

Typical coverage is about 1.5 gal/sq on granulated surfaces and about 1.0 gal/sq on smooth surfaces. The primer goes onto clean, dry and sound asphalt-based substrates by spray, roller or brush. On granulated or rough surfaces, enough material is applied to coat and condition the substrate uniformly, and the primer dries completely before the next coating layer.

• Weight per gallon: 11 lbs
• Solids by volume: 40% nominal
• Solids by weight: 44% nominal
• VOC: less than 50 g/L
• Color: light gray
• Application temperature: 40 F to 120 F
• Cure time: 3 to 6 hours at 77 F and 50% relative humidity
• Service temperature: 15 F to 180 F
• Packaging: tote, drum, 5 gallon and 1 gallon
• Clean up with soap and water; shelf life two years from date of manufacture

KoolFlex 460 is applied by trowel, brush or putty knife in a layer 1/8 inch to 1/4 inch thick over cracks, breaks, tears and holes, with a maximum build of 1/4 inch. Over cracks and breaks the material is spread 2 to 4 inches beyond the damage to feather the edges. Patch areas are checked for voids, and more sealant goes on where needed before coating. It can be applied over old, cured silicone coatings and sealants.

Adhesion is listed to concrete, masonry, vinyl, fiber cement, polyurethane foam, EPDM, aged acrylic coatings, granular cap sheet, wood, metals and Kynar. A primer may be needed. The mastic can be applied to wet and underwater surfaces. It is not mixed or thinned.

• Application rate: 24 sq ft per gallon at 1/16 inch, 12 sq ft per gallon at 1/8 inch
• Solids by volume: 60%; solids by weight: 53%
• Weight per gallon: 11.8 lbs
• Tensile strength: 300 psi; elongation: 250% nominal; tear resistance: 82 lbs/in; hardness: 70 Shore A
• Tack free in 1 to 3 hours; fully cured in 24 hours; listed cure time 24 to 48 hours at 77 F and 50% humidity
• VOC: 50 g/L
• Service temperature of the cured film: 15 F to 180 F
• Packaging: 5 gallon container for the mastic, with tote, drum, 5 gallon and 1 gallon listed in the properties table

KoolFlex 600 is the finish coat of this system. It is a high solids, single component, moisture cure elastomeric silicone roof coating whose primary intended use is on low slope roofs. It carries the mark ASTM D6694 compliant. Three standard colors are offered: white, tan and gray.

The recommended application rate for most substrates is 1.5 gallons per 100 sq ft, which equals 17 mils wet film thickness. Dry coat thickness is listed as 20 mils. The coating goes on with standard airless spray equipment or a medium nap roller, and a brush is used for small touch-up work. It is mixed well to a uniform consistency and color and is not thinned, because thinners or additives alter the intended performance and void all warranties.

• Volume solids: 95%; solids by content: 96%
• Specific gravity at 77 F: 1.30 plus or minus 0.04
• Initial elongation: 279% at 73 F and 248% at 0 F
• Elongation after 5,000 hours aging: 194% at 73 F and 229% at 0 F
• Initial tensile strength: 266 psi at 73 F and 247 psi at 0 F
• Tear strength, Die C: 30 lbf/in
• Permeance: 6.3 US perms at 73.4 F and 50% relative humidity
• Wet adhesion to SPF: 2 pli or more
• 5,000 hours accelerated weathering: pass
• Low temperature mandrel bend: pass at -15 F
• Temperature stability range: -67 F to 350 F
• Initial SRI: 109
• VOC (EPA Method 24): less than 50 g/L
• Flash point: 167 F

The silicone coating tolerates rain within about 1 hour of application and is listed as rain-safe in 1 hour. The tack-free time is 1 to 2 hours, and the skin-over time is 1 to 4 hours depending on temperature and relative humidity. Final cure takes 30 hours, and the recoat cure time is 24 hours. The coating can dry in 1 to 4 hours, and a subsequent coat goes on as soon as the previous one can safely be walked on.

Application is not recommended below 40 F, and the coating is not applied if rain is expected within four hours. Lower temperatures can affect cure time.

High viscosity calls for a high-pressure airless sprayer producing at least 3500 psi at the gun head, with a pump of at least 3 gallons per minute. Hoses are BUNA-N jacketed to prevent moisture contamination and have a minimum inside diameter of 3/4 inch. The spray gun has a reverse-a-clean tip with a minimum orifice of .030 and a 50 degree fan tip. Equipment is cleaned with 100% mineral spirits, not water or reclaimed solvents.

Before coating, surfaces are cleaned with a power washer and wire brush to remove dirt, grease, oil, mold, algae, loose granules, loose paint and rust. Primer and mastic work is applied only above 40 F and rising, with humidity under 90% and no rain for 48 hours. Surface temperature stays under 100 F to avoid premature curing, and a light water spray cools a hot roof surface.

KoolFlex 600 comes in 50 gallon and 5 gallon containers, and shelf life is 24 months, stored unopened between 40 F and 85 F. Once a container is open the curing process has begun, and the whole container is used.

Available warranties include Full System Limited Warranties ranging from 5 to 20 years. A 10 to 20 year Kool Coats Material Warranty is listed for KF-460, with a 10 to 20 year Labor and Material Warranty available for a fee. The manufacturer's warranty is non-transferable and is given solely to the original purchaser. P-305 is specified for warranty silicone systems over asphalt-based substrates.