Video by Rubber4Roofs. This walkthrough is based on the guide from "RUBBER ROOF REPAIR - how-to repair EPDM Flat Roofs" by Rubber4Roofs, a UK-based EPDM roofing supplier. The video covers the splice adhesive method for patching EPDM membrane - the technique used by trade roofers and suitable for careful DIY on small repairs. Worth watching before you buy materials, as the process is quite specific.
1. Locate the damage properly
Finding the actual source of a flat roof leak is not always obvious - water travels before it appears inside. After rain, get up onto the roof and look carefully. Likely problem spots: along seams where two sheets of EPDM were joined, around any upstands or edging trim, and around anything that penetrates the membrane such as vent pipes, skylights, or TV aerial fixings.
Run your hand over suspect areas. A lifted seam feels loose at the edge. A puncture may look like a small split or crease. Sometimes the damage is tiny and only obvious when you get close. Take your time - repairing the wrong spot means the leak continues.
2. Make sure the roof is completely dry
This is not optional. EPDM adhesive will not bond to a wet surface. Wait at least 24 hours after rain and check the patch area is dry to the touch. On north-facing roofs in autumn and winter, damp can linger - wipe the area and check again. If you are not sure, wait another day. A patch applied to damp rubber will lift within weeks.
3. Clean the repair area
Use an EPDM cleaner or methylated spirits on a clean cloth to wipe down the area around the damage. You are removing any chalking, dirt, or oxidisation from the surface. Clean an area at least 75 mm beyond the damage in every direction - your patch needs to bond to clean rubber, not just a small area directly over the hole.
Allow the solvent to evaporate fully before the next step. This takes a few minutes, not seconds.
4. Cut the patch to size
Use an EPDM patch - either from a patch kit or cut from a piece of spare EPDM membrane. The patch should overlap the damage by at least 50 mm in every direction. Round the corners of the patch with scissors. Square corners lift. Round corners stay down.
For a lifted seam rather than a puncture, measure the length of the seam that has lifted and cut a patch to cover it fully with generous overlap on both sides.
5. Apply the primer
EPDM-specific primer is essential. Do not skip it or substitute another product. Apply a thin, even coat to both the patch and the roof surface where the patch will bond. Use a brush and work quickly - primer has a short open time.
Allow the primer to become touch-dry. This usually takes 5 to 15 minutes depending on temperature. It should feel slightly tacky rather than wet. If it dries out completely before you apply the patch, apply another coat.
6. Apply the adhesive and press the patch
For small puncture patches, some EPDM patch kits are self-adhesive once primed - you simply peel and stick. For larger seam repairs using EPDM splice adhesive, apply the adhesive to both surfaces with a roller, allow it to become tacky, then bring them together carefully. You usually get one chance to position it correctly - EPDM splice adhesive bonds on contact.
Press the patch firmly from the centre outwards, working out any air bubbles as you go. Use a seam roller if you have one, or a firm finger pressure across the whole surface. Pay particular attention to the edges.
7. Seal the edges
Run a thin bead of lap sealant around the perimeter of the patch. This covers the edge and prevents water getting under it by capillary action. Smooth it with a wet finger. It does not need to look perfect, but it does need to be continuous.
Leave the repair for at least an hour before checking it, and ideally keep it dry for 24 hours while the adhesive cures fully.
When to call a handyman
Call Richard if the damage covers a large area, if the existing membrane is pulling away from the edging trim in multiple places, or if you find more than one leak source. Multiple failures often mean the original installation was not right and a patch here and there will not give you a long-term fix. At that point the roof needs a proper assessment.
Flat roof leaking or showing its age?
The Sandwich Handyman can inspect and repair EPDM flat roofs on garages, extensions, and bay windows at properties across Sandwich and nearby East Kent villages.
Contact Richard