Sikalastic 621 TC Fluid Applied Skylight Waterproofing

Sikalastic 621 TC Fluid Applied Skylight Waterproofing is a Sika Corporation system in CSI section 07 56 00. It has two parts: a cold-fluid-applied, reinforced polyurethane flashing membrane at skylight frames, mullions and other flashing conditions, and a cold-fluid-applied clear aliphatic polycarbonate polyurethane coating over glass, acrylic and fiberglass surfaces. The flashing membrane uses Sikalastic 621 TC resin. The clear coating is Sikalastic Clearglaze.

The membrane is fully bonded and elastomeric. It is installed as a one-ply, fully reinforced flashing over the surfaces that surround skylights: concrete, plywood sheathing, wood blocking and metal. The work includes substrate preparation and the glazing of the glass-to-frame interface. The installed membrane and coating do not permit the passage of water and withstand design pressures calculated under the most current revision of ASCE 7.

Two builds are written, both with a 10 year warranty. They differ only in the reinforcement, which is Sika Reemat in one and Sika Fleece 120 in the other.

• Base layer membrane flashing: Sikalastic 621 TC at 45 wet mils, about 35 sf per gal.
• Top layer membrane flashing: Sikalastic 621 TC at 30 wet mils, about 43 sf per gal.
• Base layer coating: Sikalastic Clearglaze at 20 wet mils, about 80 sf per gal.
• Top layer coating: Sikalastic Clearglaze at 20 wet mils, about 80 sf per gal.

The manufacturer's standard warranty applies, with a materials warranty of at least one year from Substantial Completion. The manufacturer of the membrane and coating has produced them for fifteen years under the same organization or a direct affiliate.

Sikalastic Clearglaze is an aliphatic polycarbonate polyurethane clear coating. It is the skylight substrate primer for the membrane flashing and a protective coating for glass, acrylic and fiberglass skylight substrates. Typical film properties are:

• Tensile strength: 350 psi.
• Elongation: 250%.
• Tear resistance: 2600 psi.
• Dry adhesion to glass: over 425 psi (Elcometer bond).
• Accelerated weathering, UV and condensation, 5000 hours (ASTM G53): no deterioration, and clarity retained.

The flashing resin is a single-component, cold, fluid-applied, moisture-triggered, aliphatic polyurethane that conforms to ASTM D7311-07. It can be brush or roller applied. Its requirements are listed here.

• Viscosity: 5 to 20 Pa.s (ASTM D2196).
• Volume solids: 80% minimum. Weight solids: 86% minimum.
• Sag resistance: no sag at 700 micrometers (0.028 in.).
• Tensile strength: minimum 270 lb/in2. Elongation: minimum 200%.
• Weathering to 5000 hours of fluorescent UV (ASTM G154) leaves no cracking or checking.
• Water vapor transmission: maximum 8.5 g/m2 per day.
• Tear resistance: minimum 33 lbf/in. Indentation hardness: 82 durometer units, plus or minus 5.
• Dynamic puncture resistance: minimum 15 joules. Static puncture resistance: minimum 45.5 lbs.

In the 621 TC data sheet, the white resin has a solar reflectance of 0.85, a thermal emittance of 0.87 and a Solar Reflectance Index of 108. VOC content is 183 g/l and solids by volume are 81%. It is not intended to sit in contact with a constant temperature below -22°F (-30°C) or above 176°F (80°C).

Sika Reemat is a random strand fiberglass mat that conforms to irregular surfaces. Sika Fleece is a non-woven, needle-punched polyester fleece. Supplemental reinforcement at structural cracks, expansion joints and horizontal-to-vertical transitions is Sika Flexitape Heavy, a nylon mesh, or Sika Joint Tape SA, a polymer-backed self-adhering membrane with a polyester fleece facer.

• Sikaflex 11FC, a one-part polyurethane sealant, is the fillet bead and penetration sealant.
• Sikaflex Hyflex 150 LM, a one-part low-modulus hybrid sealant, is the exposed finish sealant and the glazing sealant at the skylight-to-frame and skylight-to-mullion interface. Sikasil WS-295 is the alternative finish sealant.
• Metal takes Sikalastic EP Primer/Sealer or EP Primer Rapid. Concrete and masonry take Sika Concrete Primer Lo-VOC. Existing Sikalastic membrane takes Sika Reactivation Primer.

Loose and gapped flashing edges are anchored with drilled anchors, non-asphaltic adhesive or self-adhering butyl rubber tape with a fleece upper surface. Holes, cracks, joints and gaps in flashing details are sealed flush with Sikaflex 11FC or Hyflex 150 LM. Metal flashings and mullions are power tool cleaned to bare metal per SSPC SP3 or SP11. Mullion screws and bolts are torqued to the manufacturer's values and the caps reinstalled. Deteriorated glazing is removed and Hyflex 150 LM is applied along the skylight-to-frame and skylight-to-mullion interface to form a sealant cove for the flashing. Protruding fastener heads are covered with sealant. Skylight drainage is cleared. Exposed surfaces are cleaned with a biodegradable degreaser, wiped with denatured alcohol and blown clean with an oil-less compressor.

• EP Primer or EP Primer Rapid goes on cleaned metal mullions and flashings by brush or roller, at no more than 250 sf per gal on a smooth surface, and cures tack-free. Wet primer on glass is wiped off with denatured alcohol.
• A clean straight tape line is set on the glass at least 2 in. from the primed flashing. A 20 mil wet coat of Clearglaze primes the glass for the membrane and cures tack-free.
• The embedment coat of 621 TC is applied to at least 50 wet mils at 32 sf per gal. Precut Reemat or Fleece 120 is laid into the wet resin and saturated so it conforms to the mullion profile without voids or air pockets. Laps are at least 2 in. for Reemat and 3 in. for Fleece 120.
• The reinforced flashing extends at least 1 1/2 in. onto the skylight glass.
• The sealing coat is at least 20 wet mils at 80 sf per gal. With Reemat the resin dries tack-free, usually overnight, before the sealing coat. With Fleece 120 the sealing coat follows immediately.

Where the flashing extends onto the surrounding substrate, a fillet bead of Sikaflex 11FC at least 3/4 in. goes in at inside corners and curb junctions. Acceptable substrates include concrete, block, brick, solid wood, plywood, metal and most existing roofing and waterproofing.

Glass surfaces are cleaned and degreased with denatured alcohol or acetone. A vinegar wash can remove silicone caulk residue. Severely weathered fiberglass panels are sanded to remove glass fibers first. Two coats of Clearglaze are rolled on with a foam roller, each at 20 wet mils and 80 sf per gal. Each coat ends on the membrane flashing by at least 2 in., or until the termination is vertical, which seals the edge of the flashing. This skylight waterproofing system suits glass, acrylic and fiberglass glazing.