How to bond EPDM membrane to brick around a window

EPDM is chemically inert by design, which is why it lasts decades on a roof and also why it is awkward to stick. A membrane adhesive works by putting a tacky rubber layer on both faces and letting the solvent leave, so what actually bonds is rubber to rubber. Apply it to one face only, or bring the faces together while the adhesive is still wet, and you get a fraction of the strength.

Brickwork brings dust, mortar residue and moisture. Brick can hold moisture for days after rain even when the face looks dry, and solvent-based membrane adhesives do not tolerate a damp substrate. Give it dry weather and a day, and brush the surface hard rather than wiping it.

Around a window the detail matters as much as the adhesive. Water runs down, so every horizontal lap has to shed water outwards, the top edge needs to be mechanically terminated with a bar or sealed into a reglet rather than just stuck on, and the corners need to be dressed rather than stretched. A stretched EPDM corner pulls itself off over time no matter what holds it.

1. Pick dry weather and make sure the brick has had at least 24 dry hours. Check the substrate is sound, not spalling or salt-blown.
2. Brush the brick hard with a stiff brush to remove dust and loose mortar, then vacuum it.
3. Dry fit the membrane, mark its position, and fold it back on itself so half is exposed.
4. Brush EPDM contact adhesive evenly onto both the brick and the underside of the membrane, keeping a consistent thin coat.
5. Wait until both faces are touch dry and no longer transfer to a knuckle, usually 10 to 20 minutes depending on temperature.
6. Roll the membrane down slowly from the fold outwards, pressing as you go so no air is trapped.
7. Work it down firmly with a seam roller, paying particular attention to the edges and any corner.
8. Repeat for the other half, then terminate the top edge mechanically with a termination bar and seal the bar with a compatible sealant.