Roofing Cement
Definition: Roofing cement (plastic roof cement) is a thick, trowel-applied paste of asphalt, solvent and reinforcing fibres used to seal small gaps on a roof: flashing edges, nail heads, cracked shingles and the joints around vents and chimneys. It is a sealant for small repairs, not a way to waterproof an area.
What it is
Asphalt plastic roof cement is asphalt cut with solvent and filled with mineral fibres so it stays where you trowel it, even on a slope. The common US product standard is ASTM D4586. It comes in tubs for trowelling and in tubes for a caulk gun; some versions are made to go on wet surfaces so a leak can be patched in the rain.
Where roofing cement is the right tool
- Sticking down a loose or lifted shingle tab
- Covering exposed nail heads at ridge caps and flashing
- Sealing the top edge of counter flashing where it meets brick
- Small cracks and holes in a single shingle, under a patch
- Bedding the flange of a vent boot or flashing piece
Where it is the wrong tool
Instead of flashing. A gob of cement where step flashing or a kick-out should be will crack within a few seasons as the roof heats and cools, and the leak returns, often hidden behind the cement.
Over large areas. Cement smeared across a section of roof traps water under it and is not a membrane. Low-slope areas need a real membrane (see EPDM vs TPO) or a rated coating.
As a permanent fix. Treat it as a repair that buys time. If the same spot needs cement every year, the flashing or the shingles there need replacing.
Roofing cement vs other products
Roof sealant in a tube (polyurethane or polymer-modified) stays flexible longer and is often better on metal and plastic vent boots. Roof coating is a thin liquid painted over a whole low-slope roof. Roofing tar is the hot or cold asphalt used in built-up flat roofs; people often say "tar" when they mean cement.
When you are past patching
Patches age at the rate of the roof around them. If several areas need cement, compare the cost of repairs against a new roof: our free tool prices a replacement for your own house from satellite in about a minute.