Roofers use several different products to seal shingles depending on whether they are installing new shingles or repairing existing ones. For new installations, the primary sealing comes from the factory-applied thermally activated sealant strip on the back of each shingle. This strip is designed to soften and bond to the shingle below when heated by the sun, creating a wind-resistant seal. In cold weather below 40 to 50 degrees when this strip may not activate, or in high wind zones, roofers use asphalt roofing cement, also called mastic or bull, to hand-seal shingles. They apply quarter-sized dabs of cement under each tab to ensure immediate bonding. For repairs, roofers use asphalt roofing cement as the main sealant for lifting tabs, sealing around flashing, and covering nail heads. Popular brands include Henry 208 Wet Patch, Black Jack, and Karnak. For flashing details around chimneys, vents, and valleys, roofers use polyurethane sealants like Geocel 2300 or OSI Quad that remain flexible and adhere to multiple materials. For ridge caps, they use roofing cement under each cap piece. Roofers avoid silicone caulk for shingles because it does not adhere well to asphalt and can prevent proper sealing. They also use roofing tape or ice and water shield as secondary sealing under valleys and penetrations. The key is using asphalt-compatible products that remain flexible.
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