Acrylic Reinforced Coating System TPO

The Acrylic Reinforced Coating System TPO is the Metacrylics system for existing TPO roof membranes. It is published as sheet A-03, titled TPO Fully Reinforced Acrylic Restoration System, dated 09-25-17, in the Acrylic Reinforced Systems series. The Installation Spec Book covers TPO in 10 to 30 year systems on pages 7 to 10.

It is a fully reinforced TPO roof coating system, with polyester fabric embedded between two acrylic base coats.

From the TPO roof upward, the section drawing has these layers.

• Existing TPO roof.
• TPO Primer.
• Acrylic Base.
• Polyester fabric.
• Acrylic Base over the fabric.
• Metacrylics topcoats.

A note on the sheet seals and reinforces all rooftop penetrations, drains, scuppers, flashings, skylights and perimeter edge metal by 3-coursing with Metacrylics Acrylic Gel and polyester fabric.

Metacrylics TPO Primer is an all-acrylic polymer used in pigmented elastomeric roof coating basecoats. It gives adhesion to weathered thermoplastic polyolefin membrane, and coatings based on it are used over TPO that has weathered at least four years. The membrane is pressure washed at 3,000 psi first. The primer is compatible with Metacrylics Contractor Grade White, Acrylic White and High Tensile White, and is applied by brush, roller or spray.

• Viscosity, initial: 127 KU (ASTM D-6083 range 85-141 KU). pH 10. Density 11.83 lbs per gallon.
• Weight solids 66.2 percent; volume solids 52.0 percent.
• Tensile strength 147 psi initial and 237 psi after 1000 hours weathering; elongation 227 percent initial and 181 percent weathered.
• Tear resistance: 79 lbf per inch.
• Permeance: 7.0 perms. Water swelling after 7 days: 10 percent.
• Flexibility to -15 degrees F (-26 degrees C); VOC 50 grams per liter.

Wet adhesion on aged TPO is 1.5 pli, on APP modified bitumen 1.4 pli, on polyurethane foam 2.3 pli, on cement 1.3 pli, on galvanized steel 1.6 pli and on aluminum 1.6 pli; dry adhesion on aged TPO is 2.5 pli.

Water alone does not clean weathered TPO. Suitable cleaners are Metacrylics EPDM Rinse and trisodium phosphate (TSP) solutions, sprayed over the whole surface and followed by power washing with water at a minimum of 3000 psi with a wide fan tip. Ponded water areas collect the most dirt. The primer is not applied below 5 degrees C (40 degrees F), when temperatures may fall below the dew point within 6 hours, above 90 percent relative humidity, in expected rain, or on roofs with ponded water. Zinc oxide is not used in it.

In the Spec Book the 10-year coating over TPO or PVC uses 0.3 gallons of TPO Primer per square, applied to the whole roof including parapet walls, flashings and HVAC ducting and cured 4 to 12 hours, followed by 3 gallons of Acrylic White in two coats of 1.5 gallons, 24 to 48 hours apart. The 15-year system adds 3 gallons of Clear Acrylic Base and a square of fabric per square.

Acrylic Base in gray is a water-based acrylic elastomeric coating that must be protected from the sun by Acrylic White or a color coat. It contains no zinc oxide. It weighs 12.1 lbs per gallon, with a VOC content of 11.73 grams per liter and solids content of 67.9 percent by weight. Tensile strength is 156 psi, elongation 149 percent average, hardness Shore A 41, wind uplift 105 PSF, and fire resistance Class A (ASTM E-108, UL 790). Spray application embeds the fabric in 2 to 3 gallons per 100 sq. ft., then adds 2 gallons over it, for 4 to 5 gallons in all with a .061 tip and 24 to 48 hours of drying.

Stitchbond polyester fabric comes in four styles.

• T272: soft, 3 oz per sq. yd.; tensile 57.1 lbs; elongation 61.65 percent; Mullen burst 176.8 lbs.
• T325: soft, 2.75 oz per sq. yd.; tensile 31.6 lbs; Mullen burst 99.6 lbs.
• T326: firm finish, 2.9 oz per sq. yd.; tensile 41 lbs; Mullen burst 127 lbs.
• W201: warp knit mat, 2.75 oz per sq. yd.; tensile 75 lbs; Mullen burst 150 lbs.

T272, T325 and T326 rolls are 40 inches wide and 324 feet long, about 20 to 22 lbs; W201 rolls are 42 inches wide and 300 feet long.