Description/Cause: Blisters are pockets in the roofing material with a spongy feel. They are usually formed by the pressure of moisture beneath the surface of from lack of adhesion causing dry spots.
Damage Created by Condition: Foot traffic, especially during colder temperatures can rupture the membrane, allowing water to enter the roofing system and the interior of the building.
Suggested Maintenance/Products Required: Spud back aggregate if present, and sweep clean of debris. Make an “x” cut across the blister, extending through all raised piles. For bitumen based roofs, fold segment back and leave open to allow drying of moisture. Trowel Karnak #19 Flashing Cement under each segment so that felt does not touch felt. Press each segment into place to insure bonding. Continue by applying KARNAK #19 Flashing Ultra Rubberized Flashing Cement per directions to extend at least 4” beyond x. Embed KARNAK #34 Asphalt Saturated Membrane or KARNAK #31 Fiberglass Membrane over the entire area and cover with additional layer of flashing cement. Smooth with trowel and replace aggregate, if present. For repairs of blisters in ponding areas use KARNAK #229AR Elastomeric Trowel Grade.
*The repair product to be used will depend on the roofing substrate. For Single ply such as EPDM, TPO, PVC, Hypalon or Acrylics and Metal, Karna-Flex (502MS or 505MS water-based) may be used for repairs.
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