How Flat Roof Repairs Are Done For Seam Gaps In Rubber And Plastic Roofing Membranes

5 January 2023
 Categories: , Blog


Buildings on flat roofs often have membrane roofing. The membrane might be made of plastic or rubber, but they both have a potential weak area, and that is along the seams. When the roofing gets old, the bond between the seams starts to deteriorate. If a seam splits open, your building is at risk of a roof leak. Here's a look at how flat roof repairs are done for leaky seams.

For Rubber Membrane Seams

Rubber roofing seams are joined together using seam tape and sealant. The exact method used depends on the products the roofer chooses. The roofer starts this type of flat roof repair by cleaning the area around the seam. They may need to scrub it clean or use a pressure washer.

Once the membrane is dry, primer can be painted over the seam gap. Cleaning the membrane first helps the primer adhere better. The primer is painted over the seam and along a border a few inches beyond the seam.

Next, a wide strip of fleece-backed seam tape is positioned over the seam. The tape comes on a standard-size roll and is generally large enough to cover the seam with a few inches of overlap. The tape is pressed into the primer by hand and with a roller so it sticks well.

A thin layer of silicone sealant is then spread over the tape. Another layer of tape is applied and pressed into the sealant, and then one more layer of sealant is added to the top. This multi-layer patch repair will protect the roof from leaking and keep the seam sealed for a long time to come. However, the patch should be checked regularly when doing other roof maintenance to make sure it's holding well.

For Plastic Membrane Seams

Some flat roofs have membranes made out of plastic instead of rubber. These seams are bonded in a different way. Instead of using seam tape and sealant, they are bonded with heat. When a plastic membrane is first installed, the contractor may use a machine to heat-weld the membrane. When doing roof repairs, the roofer will probably use a hand welder.

The hand welder has a flat pointed tip the roofer places under the top membrane. The welder blows out heat that makes the membranes melt just enough to fuse together. To get the membranes to stick to each other, the roofer rolls over them with a hand roller. As the roofer works along the loose seam, one hand controls the welder while the other controls the roller.

The result is a tight bond between the two membranes so the gap is sealed. The roofer can check their work with a seam tool they use to try to pry the seam apart. The seam should stay tight without having any tiny gaps. Heat-welding a seam gap is one of the easier flat roof repairs to have done.

For more information about flat roof repairs, reach out to a local contractor.