Gravel BUR Silicone

Gravel BUR Silicone is a Kool Coats restoration system for gravel-surfaced built-up roofs (BUR) in the USA market. Its coating chemistry is silicone. A prepared BUR roof receives P-305 asphalt bleed-block primer, compatible detail repairs and a KF-600 KoolFlex silicone finish.

The system is used on serviceable BUR roofs with a worn surface, where sunlight and water retention are the main restoration concerns. It is one of the silicone coatings for built-up roofs from Kool Coats.

Loose gravel is removed and wet or unstable areas are resolved first. The specified asphalt bleed-block primer is applied after gravel removal and roof repairs. Compatible detail treatment follows, and KF-600 is installed to the required cured thickness. Future maintenance uses compatible silicone recoats.

• Primer: P-305 Asphalt and Bleed Block Primer
• Details: KF-460 KoolFlex Mastic
• Coating: KF-600 KoolFlex high solids silicone

The assembly is a bleed-blocked silicone overlay: a bleed-block primer, then solvent-free KoolFlex high-solids silicone. It is recoatable with silicone only. It is intended for moderate to severe wear conditions.

P-305 is a water-based acrylic primer that controls asphalt bleed-through and smooths granulated surfaces before silicone is applied. It fills surface voids on granulated modified bitumen, which helps silicone build to the required mil thickness. It is specified for warranty silicone systems over asphalt-based substrates.

• Coverage: about 1.5 gal per square on granulated surfaces and about 1.0 gal per square on smooth surfaces
• Weight per gallon: 11 lbs
• Solids by volume: 40%, nominal; by weight: 44%, nominal
• VOC: under 50 g/l
• Color: light gray
• Application temperature: 40 to 120 degrees F
• Cure time: 3 to 6 hours at 77 degrees F and 50% relative humidity
• Service temperature: 15 to 180 degrees F

It is applied by spray, roller or brush to clean, dry and sound asphalt-based substrates. On granulated or rough surfaces, enough material is applied to coat and condition the substrate uniformly, and the primer dries completely before the next coat. Containers are tote, drum, 5 gallon and 1 gallon.

The surface is power washed and wire brushed free of dirt, grease, oil, mold, algae, loose granules, loose paint, rust and excess chalk. Application is made above 40 degrees F and rising with humidity below 90% and no threat of rain for 48 hours. Surface temperatures stay under 100 degrees F, and a light water spray cools a hot roof surface. Primer and mastic are stored two years from date of manufacture at 60 to 90 degrees F.

KF-600 is a single-component, moisture-cure elastomeric silicone. Its primary intended use is on low-slope roofs, and it is listed for smooth and granulated surface BUR. It is ASTM D6694 compliant and comes in White, Tan and Gray.

• Volatile organic content: under 50 g/l
• Flash point: 167 degrees F
• Shelf life: 24 months, in unopened containers at 40 to 85 degrees F
• Containers: 50 gallon and 5 gallon
• Skin-over time: 1 to 4 hours, depending on temperature and relative humidity

Once a container is opened, curing has begun, and the entire container is used. Leftover material is allowed to solidify. Equipment is cleaned with 100% mineral spirits, not water or reclaimed solvents. The coating is not applied in rain expected within four hours or below 40 degrees F.

KF-460 is a 100% silicone mastic for sealing and repairing roofs, flashings, walls, masonry and metal roof seams and fasteners. It builds up to 1/4 in, has a hardness of 70 Shore A, and has a tear resistance of 82 lbs/in. The service temperature of the cured film is 15 to 180 degrees F. It is not recommended for interior use, or for application below 35 degrees F or within one hour of expected rain. The data was revised in January 2025.

Full System Limited Warranties for KF-600 range from 5 to 20 years. P-305 is specified for the warranty silicone systems over asphalt-based substrates. KF-460 carries the Kool Coats 10-20 year Material Warranty, with a Labor and Material Warranty available for a fee.