WCP-MTL1-4.5E — Metal roof acrylic restoration system

WCP-MTL1-4.5E is Western Colloid specification number WCP-MTL1-4.5E, titled Elastomeric Metal Roof Sealing, Metal Roof Refurbishing with an acrylic reflective surface. It belongs to the Western Cool Roof Systems group and is classed as a commercial roof coating system for commercial roof restoration. The specification was revised 10/20.

The system is an elastomeric, water-based, fluid-applied coating for existing metal roofs. The 4.5 in the code is the total ElastaHyde application rate in gallons per 100 square feet. A sibling code, WCP-MTL1-3E, uses the same materials at a lower rate.

Existing exposed-fastener and seamed metal roofs with a metal roof restoration scope are the intended substrate, including Kynar prefinished panels once primed.

The assembly meets these named criteria:

• UL Class A
• Factory Mutual Class 1
• California Title 24
• LEED (USGBC)
• ENERGY STAR

ENERGY STAR status rests on the white ElastaHyde. Energy savings are reduced when colors other than white are used.

The system has three working layers: preparation materials, seam and flashing materials, and a reflective surface coating.

• Surface cleaner: TSP (tri-sodium phosphate) or a low-foaming industrial detergent.
• #900 Metal Bonding Primer for adhesion to metal substrates including Kynar prefinished panels.
• #900R Rust Primer where rust is present, or an approved corrosion primer for the metal type.
• #800 Elastic Cement, a water-based elastomeric flashing, sealing and repairing compound used with polyester fabric at deck and wall transitions, edges, curbs, pipes, skylights, panel ends, side laps and seams. It can be used on vertical as well as horizontal surfaces.
• Stitchbonded polyester fabric reinforcement, available in several widths.
• ElastaHyde #720 ARC or #790 AFC, a 100% acrylic white reflective coating that meets ASTM D6083/6083M-18. White is the standard color and other colors are available.

Preparation for this specification runs in a set order.

• Voids or gaps of 1/4 inch or more in the metal are closed with self-tapping screws to bring the sides flush; voids are patched with sheet metal fastened with self-tapping screws.
• Loose or missing fasteners are replaced or tightened. Stripped, severely corroded or damaged fasteners are replaced with a larger-diameter fastener, and missing or weathered washers are replaced with butyl rubber or acceptable washers.
• Loose, flaking or peeling coatings and cracked or heavily built-up old repair compounds are removed with a stiff broom, wire brush or scraper.
• The roof is cleaned with a broom or brush and detergent. A pressure washer may be used. The roof is rinsed and left to dry.
• Rusted or oxidized areas are treated with #900R Rust Primer at no more than 1/2 gallon per 100 square feet, in a light, uniform coat without pooling.
• Most aged, cleaned metal surfaces need no primer. Kynar prefinished metal is primed over its whole surface with #900 Metal Bonding Primer at 1/4 to 1/2 gallon per 100 square feet and left to dry at least 24 hours before coating.

Every exposed fastener head is covered with Elastic Cement, applied with a small brush, finger or bulk caulking gun, and bonded to the metal around the head.

Roof seams, roof jacks, pipes, flashings, metal edges, skylight panels and air conditioning ducts are sealed by a three-course method at a total rate of 10 square feet per gallon:

• A coat of Elastic Cement about 5 to 6 inches wide and 1/8 inch thick is brushed on.
• A 4 inch wide polyester fabric is embedded in the wet cement and smoothed with a brush so there are no voids or wrinkles. Fabric 6 or 12 inches wide bridges wider or irregular seams.
• A second coat about 1/16 inch thick follows at once.

Where old sealing compound remains, the new seal is at least 2 inches wider than the old. A single application of Elastic Cement is limited to 3/16 inch. The fabric must not tent over a fastener head; a 1/2 inch straight or X cut is made in the fabric at each head so it lies flat. After drying, voids, severe wrinkles and fishmouths are repaired with more cement and fabric.

ElastaHyde is applied at a total of 4.5 gallons per 100 square feet to the whole roof surface, including flashings, pipes, curbs and the areas sealed with Elastic Cement. It goes on in three uniform coats, each about one third of the total rate, by roller, brush or airless spray. The result is an average dry thickness of 36 mils after cure.

Spray application is cross-hatched, with each coat at a right angle to the previous one. Each coat dries for 24 hours before the next. Material is not allowed to pool, and excess is brushed out before it dries. Exposed air conditioning ducts can also be coated. After the coating has dried, the roof is checked for voids and touched up.

Approximate estimating figures:

• Elastic Cement: 10 square feet per gallon, or about 25 linear feet per gallon at a 5 inch width and 20 linear feet at 6 inches. One gallon is added for every five roof jacks or pipe flashings.
• ElastaHyde: about 22 square feet per gallon. At least 15% is added to the area for corrugated metal roofs, and other profiles may need more.
• Polyester fabric: estimated from the linear feet of seam and flashing.

Application temperature is a minimum of 55 degrees F and rising. The materials are not applied when temperatures will drop below freezing before they dry, or when rain, snow or freeze is expected within 48 hours. Materials are stored at 45 degrees F or above and protected from freezing.

Published values for white ElastaHyde #720 ARC: initial solar reflectance 84% (ASTM C1549), initial thermal emittance 89% (ASTM C1371), SRI 106 initial and 93 aged, Class A fire rating under UL 790 and ASTM E108, elongation above 250% initially, tensile strength above 250 psi, CRRC product ID 0682-003. Elastic Cement has elongation above 500%, 65 to 70% solids by weight, and a minimum application temperature of 50 degrees F.