Silicone Roof Coating System Tar and Gravel

Silicone Roof Coating System Tar and Gravel is a Metacrylics system assembly for tar-and-gravel built-up roofing. It is a silicone roof coating restoration system with silicone finish coats, and its drawing is dated 09-25-17.

The drawing carries two notes. The first states that once the silicone restoration system is complete the roof surface will not be smooth, because the finish will be bumpy from the aggregate embedded in the existing tar surface. The second requires all roof top penetrations, drains, scuppers, flashings, skylights and perimeter edge flashing to be sealed or reinforced with Silicone Gel or a 3-course build-up of silicone and polyester fabric.

The primer has two options: Metacrylics Acrylic Roof & Tile Primer or Metacrylics Acrylic Bleed Block Primer. The silicone topcoats are applied over the primer, with detail materials and polyester fabric used where the drawing and the book call for them.

The silicone application book covers tar and gravel at two levels.

• 15-year system: Acrylic Bleed Block Primer or Acrylic Clear Base at 1.5 gallons per square, then HS Silicone at 3.5 gallons per square in two applications of 1.75 gallons per square.
• 20-year system: the same primer at 1.5 gallons per square, then HS Silicone White at 4.5 gallons per square in two applications of 2.25 gallons per square.

The steps start with spudding or tearing off the gravel so that all loose gravel is gone, then clearing debris and dust and pressure washing. Penetration details follow the primer. Where the old roof has been completely removed and the surface is smooth, the primer rate drops to 1 gallon per square in the 15-year system.

The book gives details for the rooftop items on a tar-and-gravel roof.

HVAC ducting is pressure washed, duct joints get Silicone Gel with no reinforcement or a 3-course with Acrylic Gel and fabric, and 2 gallons per square of HS Silicone goes on in two applications of 1 gallon per square.

For skylights, Silicone Gel or a 3-course is carried up the side of the curb at least 3 inches and onto the roof surface 3 inches. Weep (drainage) holes in the skylight are not covered, and exposed screw heads get Silicone Gel.

Pitch pockets are filled with HS Silicone or Silicone Gel. Gel then goes over the top and down to the base of the pocket and at least 3 inches onto the roof, and up and around the penetration from the pocket a minimum of 6 inches.

Scuppers and drains lose all old asphalt, mastic and roofing material first. Acrylic Clear Base is the primer. For scuppers, Silicone Gel goes inside and outside a minimum of 4 inches. For drains, gel goes inside the drain pan and down the drain pipe a minimum of 2 inches and around the drain a minimum of 8 inches.

Metacrylics Acrylic Bleed Blocker Primer is an all-acrylic primer that gives resistance to asphalt staining and adhesion to the substrate. Asphalt substrates can bleed through acrylic and silicone coatings, and this primer is the water-based barrier against that.

Typical values: total solids 27.5 ±0.5% by weight, pH 9.5 ±0.3, specific gravity 1.05, density 8.76 lbs/US gal, viscosity 100–400 cps (Brookfield), Tg -10°C (14°F), and storage stability unchanged at 10 days at 60°C. It should be protected from freezing.

The minimum application is 4 dry mil, about 1 gallon per square, over unaged asphalt substrates. Two coats of 8 dry mil each may be needed on unaged asphalt. Discoloration of the wet coating over aged asphalt is water soluble and disappears after a few rainfalls.

Limits: not below 5°C (40°F), not above 90% relative humidity or with rain expected, and not when temperatures can be expected to fall below the dew point within the next 6 hours.

It is packaged in a 5 gal (18.93 L) pail or a 55 gal (208.2 L) drum.

White, light gray and tan are the standard colors, and custom colors are made on request with 15 additional days for non-standard colors.

Duometer hardness is Shore A 45–55, and tear strength is 45 lbs/in.

The film measures 2.0 U.S. perms, and ASTM D-570 water absorption is 0.2.

Reflectivity is 88%, emissivity is 91% and SRI is 110.

It is not recommended for continuous immersion service, for cryogenic tanks, or for cold storage roofing without a vapor barrier.

Spray equipment is a high-pressure airless pump producing at least 3500 psi at the gun head and at least 3 gallons per minute, fed by a 5:1 transfer pump to prevent cavitation.

Hoses need a BUNA-N jacket and a minimum I.D. of 3/4 inch.

It can be applied at lower temperatures, but the cure time is extended.

Before any surface is coated, an adhesion test to ASTM D-903 checks that the coating will adhere.

The coating cures by reacting with moisture, so uncured material is not left in guns, pumps or hoses for long periods unless the equipment has moisture lock hoses, fittings and seals.

Recoating of existing spray-in-place roofing systems is permitted over a cleaned and completely dry surface.

Tested material complies with ASTM D-6694-01, the standard specification for liquid-applied silicone coating used in spray polyurethane foam roofing.

Packaging is a 2 gallon or 3.5 gallon bucket, and the color is white.

Hardness is Shore A 45–55, tear strength is 45 lbs/in, tensile strength is 300 psi (Die C, ASTM D-412) and elongation is 200%.

No degradation appears after 5,000 hours of QUV weathering, and the gel measures 7.9 U.S. perms.

Containers are kept closed in a dry, cool place above 65°F (18°C), on wood pallets rather than concrete floors.

Spot repairs, reinforcement of seams, flashings and penetrations, and sealing of solar and air conditioning joint and penetration repairs are the typical uses.