How long does roof tar take to dry?
Short answer. It depends on the product. Asphalt roofing cement, the thick 'roof tar' sold in tubs and tubes, usually skins over within hours to a day but can stay soft underneath for days or weeks, especially in cool weather. Liquid roof coatings and sealants list their own rain-safe and full-cure times on the label, and warm, dry weather speeds all of them up.
What people mean by roof tar
- Asphalt plastic roofing cement: a thick, solvent-based paste troweled onto flashing and small repairs. It is designed to stay somewhat flexible, so it never gets rock hard.
- Wet-surface roofing cement: a version formulated to stick to damp surfaces for emergency patches in the rain.
- Liquid roof coatings: brushed or rolled onto low-slope roofs; drying and cure times vary widely by type.
- Hot tar: used on older built-up flat roofs and applied by professionals; it hardens as it cools.
What affects drying time
- Temperature: solvents evaporate slowly in cool weather, so a winter patch stays soft much longer.
- Thickness: a thick glob takes far longer to firm up than a thin layer and may never fully cure inside.
- Sun and airflow: warm sun speeds the surface skin.
- Product formula: always follow the label's stated times.
Why tar is a temporary fix on shingle roofs
On a pitched shingle roof, tar smeared around a pipe, chimney, or wall usually covers a failed part instead of replacing it. As the cement ages in the Georgia sun it shrinks, cracks, and lets water back in, often in a way that is harder to repair later. Cracked pipe boots should be replaced and chimney flashing reworked. See pipe boot leaks and roof flashing explained.