Flat Roof Repair Tips

If you’re looking for information on flat roof repair, you’ve come to the right place. The procedure varies depending on the type of roofing system, but here are the steps for the most common type where I live.

It’s called “modified bitumen” (pronounced buy-TOO-men) and consists of a tough mat embedded in a special asphalt formulation that includes elastic additives. That allows the material to expand and contract with changes in temperature. The surface is covered with ceramic granules to provide sun protection.

Modified bitumen, or “modified” as it is often called, is especially popular on small residential jobs. This is because it doesn’t require a hot asphalt boiler along with the inherent safety risks and unpleasant fumes.

Modified can be installed in several different ways, but one of the most common methods is with a propane torch. That is also the technique responsible for most of the leak problems with this system when the seams are not heated properly. If you overheat the material, too much asphalt will come out of the seam. Insufficient heat results in cold seams that are not fully joined. Either case creates seams that are vulnerable to water intrusion. If the roof collects water and the roofer did not install a protective interlayer, leaks are almost inevitable.

Fortunately, this is a fairly simple flat roof repair. You will need these materials:

Flashing cement. Be sure to get the MB (modified bitumen) variety, as the standard type is not 100% compatible.

Membrane. Either 4″ or 6″ is fine, but be sure to get fiberglass instead of cotton as it lasts much longer.

granules For a small repair, you may find enough slack on the roof or in the gutter to reuse.

Start by CAREFULLY probing the seams with a small utility knife, looking for gaps. Ideally, the seams should have about ½” of asphalt bleed. Any areas that are not suspicious.

Seams must be clean and dry to get a good flat roof repair. Spread a thin layer of flashing cement directly over the problem area, slightly wider than your membrane. Test the joint you are making by “tapping” the cement with your trowel. If it comes off, leaving bare patches of modified, the surface is still too wet or too dirty.

Then, keeping the membrane taut, place it on the thin layer of flashing cement. Work with your trowel until the membrane is firmly embedded.

Then spread another layer of flashing cement over the membrane. Again, you don’t need much. Just enough to cover the mesh is enough.

To complete your flat roof repair, sprinkle granules into the fresh cement. This will dress the repair and protect it from the sun.