Sikalastic-621 Metal Roof Recover

Sikalastic-621 Metal Roof Recover is the Sikalastic RoofPro Direct Metal guide specification, written as CSI section 07 56 00, Fluid-Applied Roofing. Its scope is all labor, materials, transportation, equipment and services needed to install a Sikalastic RoofPro waterproofing system on new or existing metal roofing, on a substrate the manufacturer approves. The related sections are 05 30 00 Metal Decking, 07 60 00 Flashing and Sheet Metal and 07 72 00 Roof Accessories. Referenced standards bodies are ASTM, NRCA and ASCE.

The coating in the system is Sikalastic 621 TC, a cold-applied, elastomeric, aliphatic, single-component, moisture-triggered polyurethane resin. It is part of the Sikalastic 621 roofing system, which pairs the resin with fiberglass mat or polyester fleece reinforcement as a membrane and flashing system.

The metal roof build is the lightest of the 621 TC system guides.

• Primer: chosen from the priming guide.
• Base layer: Sikalastic 621 TC at 20 wet mils, 80 sf per gal.
• Top layer: Sikalastic 621 TC at 20 wet mils, 80 sf per gal.
• Detailing: Sika Flexitape Heavy or Sika Joint Tape SA centered over seams, transitions and properly treated cracks and joints.
• Minimum dry film thickness: 32 mils.

Metal surfaces named in the priming guide are aluminum, galvanized steel, cast iron, copper, lead, brass, stainless steel, steel and zinc. All of them take Sikalastic EP Primer/Sealer or EP Primer Rapid. Pre-coated metal and aluminized solar reflective coatings take the same primers, and metal substrates need surface evaluation and field adhesion testing.

• Packaging: 5 gal. (19 L) pail.
• Colors: white, pearl gray and steel gray, with custom colors at a minimum order quantity.
• Shelf life: 9 months. Storage: dry, at 35 to 77°F (2 to 25°C).
• Density: about 12 lb./gal. VOC content: 183 g/l. Solids by volume: 81%.
• Solar reflectance: 0.85 for white (ASTM C1549). Thermal emittance: 0.87 (ASTM C1371). Solar Reflectance Index: 108 (ASTM E1980).
• External fire performance: Class A (ASTM E108).
• Service temperature: -22°F to 176°F (-30 to 80°C).
• Approvals and standards: ASTM E108, ASTM D6083 and ASTM C836.

The resin stays flexible at low temperatures and is vapor permeable. It resists ponding water and roots, and an existing Sikalastic membrane can be recoated without stripping. It is not used under continuous immersion.

Metal seams and plywood or cover board joints are covered with a 40 to 45 mil resin layer embedding 3 in. or 6 in. Sika Flexitape Heavy centered over the seam, or with Sika Joint Tape SA. Transitions between dissimilar materials get the same resin layer embedding Flexitape Heavy or Joint Tape SA centered over the edge. Cracks up to 1/16 in. need no detailing. Cracks from 1/16 in. to 1/4 in. are routed, sealed with Sikaflex and covered with a 40 to 45 mil resin layer embedding 3 in. Flexitape Heavy. Joints from 1/4 in. to 1 in. take bond breaker tape and 6 in. Flexitape Heavy, with the mat or fleece ending at the edges and overlapping the tape by at least 2 in. each side. Joints wider than 1 in. are treated as expansion joints.

Ferrous metal is ground or blast cleaned to SSPC-SP3 through SP11 before priming. Nonferrous metal is cleaned of dust and oxidation and abraded to bright metal, and wire brushing suits galvanized and soft metals such as lead and copper. Grease is removed with a solvent wipe or a detergent wash, and stainless steel is mechanically abraded or ground to create an anchor profile.

Where the roof is fully reinforced, the 621 TC data sheet defines further system guides. With mat reinforcement, the Sikalastic 10 and 15 builds use a base layer of 35 and 45 wet mils with a 30 mil top layer, while the Sikalastic 20 and 25 builds use a 45 mil base layer. Sikalastic 25 adds a second 30 mil top layer. With Sika Fleece 120, 140 and 170, the Sikalastic 15, 20 and 25 builds use base layers of 45, 50 and 60 mils with top layers of 30, 35 and 40 mils. Minimum dry film thickness runs from 51 to 85 mils for mat builds and 61 to 85 mils for fleece builds.

With mat, the base resin is rolled on with a 1/2 in. nap phenolic resin core roller, or squeegee or spray applied and backrolled. The mat goes into the wet resin with seams overlapped at least 2 in., frayed edge over the cut edge of the roll, and a wet roller saturates it. After about 5 minutes the binder dissolves so the fibers conform to irregular surfaces. The base layer cures 12 hours at 70°F and 50% R.H., or until tack free, and the top layer follows within 7 days. In the 25 year build the first top layer cures 12 hours before the second.

With fleece, two-thirds of the resin is rolled onto the primed substrate and the fleece goes in wet, overlapped at least 3 in. along edges and 6 in. end to end. A wet roller saturates it with light pressure to remove air pockets, and the remaining third of the resin follows immediately.

Pot life in an open container is about 1 hour at 75°F. Ambient air is 41 to 95°F, relative humidity 80% maximum, and substrate moisture 4% or less. Overcoating waits 14 hours at 40°F, 6 hours at 50°F and 5 hours at 70°F. After 7 days, Sika Reactivation Primer is applied before further coats.

Areas with direct foot traffic carry aggregate in a supplemental resin layer, never in the top layer of the membrane. The seed and back roll option applies 15 wet mils of 621 TC resin to the cured membrane, seeds it with aggregate and back rolls it. It is intended for maintenance traffic and enhanced slip resistance. Wear coats are required where heavy or frequent foot traffic occurs.

The metal roof system fits the restoration of existing metal roofs that use a reinforced liquid-applied coating.