Roofing tar, usually sold as roof cement, can stop a small leak for a while, often months to a year or two. It is not a lasting repair. In the sun it dries out, shrinks and cracks, and water finds its way back in. Tar works best as an emergency patch on a dry surface and as a sealant under flashing, not as the main fix.
Roof cement versus other products
| Product | Best use | Lifespan on its own |
|---|---|---|
| Roof cement (tar) | Small patches, under flashing edges | Months to a couple of years |
| Roofing sealant in a tube | Nail heads, small gaps | About one to a few years |
| Liquid rubber or elastomeric coating | Flat and metal roofs, whole surfaces | Several years when done right |
| Spray sealers | Emergency patch | Short term |
Where tar works
- A quick patch over a small hole or cracked shingle to get through a storm
- Sealing under the edges of new flashing as part of a proper repair
- Around nails and fasteners that cannot be covered by another layer
Where tar fails
- Smeared along a chimney or wall in place of flashing
- Around a cracked pipe boot instead of replacing the boot
- Over a large area of worn shingles
- On a wet surface, where it never sticks
- In valleys, where running water washes it out fast
Why we see so much tar
On many older Pine Bluff homes, we find layers of tar around chimneys, vents and walls from years of quick fixes. Each layer bought a season. None of them fixed the leak. Tar also hides what is underneath, so we often find rusted flashing or rotted decking when we remove it. See chimney leak repair and roof flashing repair.
How to use tar as a temporary patch
- Wait for a dry day. Only work on a low, dry roof you can safely reach.
- Clean loose granules and dirt from the area.
- Spread roof cement with a putty knife over and past the damage.
- For a larger gap, press a piece of fiberglass mesh into the first layer, then cover with a second layer.
- Schedule a proper repair soon.
See temporary roof leak fixes.
Does tar work on flat roofs?
Older flat roofs were built with hot tar and gravel, and patching those with roof cement can hold for a time. On modern EPDM rubber or TPO roofs, tar does not bond and can damage the membrane. Those need patches made for their material. See flat roof leak repair.
Does tar work on metal roofs?
It sticks at first, but metal moves a lot with heat, so tar cracks fast. Metal roof leaks are usually at screws and laps, which need new screws and proper sealant. See metal roof leaking at screws.
How to remove old tar before a repair
Old tar is scraped off with a flat bar or putty knife, usually on a cool morning when it is stiff. It often comes off with the shingles or flashing it was holding. We check what is underneath, photograph it and replace any rusted flashing or soft wood before closing it up.
How long does roofing tar last?
Often months to a year or two in full sun.
Can I put tar on wet shingles?
Some products are made for wet use, but most bond poorly. A dry surface works far better.
Is tar bad for my roof?
Small amounts used right are fine. Large amounts over flashing and shingles hide damage and make repairs harder.
Should a roofer use tar for repairs?
As a supporting sealant, yes. As the whole repair, no.