How to Repair EPDM Rubber Roof Seams

If your commercial building has an EPDM rubber roof membrane, it’s crucial to keep an eye out for problems and to correct them properly in order to prevent further damage and leaks to the building’s interior.

If, during a routine inspection of the roof, any rippling, gaps, or tearing are discovered, the following steps should be performed to secure the laps or patches.

  • Pull back the lap to a secure point in the seam and remove debris.
  • If there is evidence of a leak, inspect the insulation and decking material. Replace wet insulation and make any necessary deck repairs before applying a patch over the damaged area.
  • Next, clean the lap edge, and secure with seam adhesive designed for EPDM rubber, prior to installing the patch.
  • Prepare the surface of the rubber by cleaning away any contaminants or debris within at least a six-inch area of where the patch will meet the EPDM rubber. If the repair point is at an area of flashing, do the same to the flashing. If there is any field-applied coating, remove this as well.
  • Clean the area with water and mild trisodium phosphate soap, using a bristle brush. Rinse and allow to air dry, or quicken the process with a squeegee and clean lint-free cloths.
  • Cut the EPDM rubber patch large enough to go four inches past the damaged area on all sides, rounding the corners of the patch to prevent peeling.
  • Use a solvent recommended by the membrane manufacturer to clean the area to be repaired. Use a clean side of the cloth for each pass in order to prevent dirt from being redistributed into the membrane. Allow the area to thoroughly dry, so that there is streaking remaining. If the manufacturer cannot be determined, you can use unleaded gas, xylene, or heptane to clean the area.
  • Apply compatible primer to both the existing EPDM rubber surface as well as the patch, and allow to dry.
  • Apply compatible adhesive to the patch and the membrane, according to the adhesive’s instructions. For EPDM, this will be a butyl-based adhesive. It is vital that the adhesive is applied at the recommended thickness in order to hold up over the long term. Allow the adhesive to dry thoroughly.
  • Put the two surfaces together, smoothing them together with even pressure from a gloved hand. Use a roller to secure the bond.
  • Apply lap sealant to the lap edge. You can also add a piece of six-inch wide flashing for added protection. If flashing is used, apply the lap sealant to the edges of this strip rather than along the EPDM rubber lap.
  • If applicable, replace ballast material over the repair once the sealant has dried to the touch.

Taking the time to perform each step properly will maximize the chances of the repair holding. Any dirt or debris left on the membrane’s surface before patching it can interfere with the integrity of the repair, making a clean work area the most important component of the process.