How to Install a Fully Adhered EPDM Roof: Adhesive, Open Time and Rolling In
Fold it back, coat both faces, wait for the tack, roll it in. The whole job is timing and keeping wrinkles out.
- Advanced
- 1 day for a small roof
- Updated
The short answer
To install a fully adhered EPDM roof, unroll the sheet and let it relax, fold it back in half, apply bonding adhesive to the deck and the underside of the membrane, wait until the adhesive is tacky and does not transfer to a dry finger, then roll the sheet into the adhesive without wrinkles and broom it down. Work in sections, and keep adhesive off the seam area.
A fully adhered EPDM roof is glued down across its whole surface. That makes it light, quiet and resistant to wind uplift, and it is the usual choice for house roofs, decks and garages. The method depends on contact adhesive, which is applied to both the deck and the back of the membrane and allowed to dry to a tacky state before the two are pressed together.
The skill is timing. Adhesive that is too wet does not grip and leaves bubbles. Adhesive that has dried too long does not bond at all. Temperature, humidity and sun change the drying time, so the work is done in sections small enough to glue before the adhesive skins over. Wrinkles, fishmouths and trapped air are the signs of a rushed job.
Prepare the deck first: see how to prep a roof deck for EPDM. Once the field is down, the seams follow in how to seam EPDM with seam tape, and then the flashing details.
Tools
- Paint roller with solvent-resistant cover or notched squeegee
- Stiff push broom
- Hand seam roller
- Utility knife with hook blade
- Tape measure
- Chalk line
- Clean rags
Materials
- EPDM membrane, 45 or 60 mil
- Bonding adhesive, water-based or solvent-based
- Seam primer and splice tape
- Uncured flashing and pre-molded boots
- Termination bar and sealant
- Cleaner recommended by the manufacturer
Safety first
- Solvent-based bonding adhesive is flammable and its fumes are harmful. No flames, sparks or pilot lights, good ventilation, gloves and eye protection.
- Rollers and rags soaked in solvent adhesive can ignite. Keep them in a closed metal container and dispose of them safely.
- Wet adhesive on the deck is slippery and sticky. Keep clear of the glue edge while working, and mind the roof edge, since WorkSafeBC fall protection applies at 3 metres (about 10 feet) and wherever a fall of any height could cause serious injury.
- A sheet with wind under it can pull a worker toward the edge. Do not unroll full width sheets in a breeze.
Step by Step
Step 1: Unroll, relax and position the sheet
Unroll the sheet in place and square it to the roof. Let it relax flat, longer in cold weather, so the curl falls out. Leave 3 to 4 inches of overhang at edges to trim later, and slack at inside corners so it is not pulled tight.
Start at the low edge near the drain or eave, so any seams lap to shed water. Weigh the sheet down if it is breezy.
Step 2: Fold the sheet back in half
Fold the sheet back on itself in a loose fold, not a hard crease, so half the deck is bare. Keep the fold straight, because a crooked fold makes the glued half lie crooked. Mark the position of the edge with chalk so you can put it back exactly.
On larger roofs, fold it back in thirds or work in sections of a size one person can glue while the adhesive is tacky.
Step 3: Apply bonding adhesive to the deck and the membrane
Stir the adhesive thoroughly, then roll it on in a smooth, even coat with no puddles or gaps. Coverage is commonly about 50 to 70 square feet per gallon for the two surfaces together, but the can gives the real figure. Apply adhesive to both surfaces so the membrane and substrate can grab each other.
Keep adhesive at least 3 inches back from the edge of the sheet where the seam will go, or as far as the tape manufacturer specifies, because splice tape must bond to clean rubber. Mask the edge with a strip of tape if needed.
Do not apply adhesive to a wet or frosty surface, and do not use solvent adhesive on foam insulation that it would dissolve. Check the substrate compatibility on the data sheet.
Watch out: Solvent adhesive is flammable. No flames, sparks, cigarettes or pilot lights near the work, and keep used rags in a closed metal can.
Step 4: Wait for the adhesive to become tacky
Touch the adhesive lightly with a clean, dry knuckle. When it is tacky, like the back of tape, but no adhesive comes off on the finger, it is ready. Water-based adhesive turns from white or pale to clear or darker as it dries, and solvent adhesive loses its gloss. Drying time is shorter in sun, wind and heat and much longer in the cold and damp. Confirm the open time on the product instructions.
If the adhesive skins and dries hard before the sheet is rolled in, it will not bond. Do not glue more than you can roll in during the window.
Step 5: Roll the membrane into the adhesive
Roll the sheet back onto the deck in a smooth, steady motion, feeding it in from the fold with no tension and no air under it. Do not stretch it. The moment it touches the adhesive it grabs.
Immediately broom it flat with a stiff push broom, working from the centre to the edges, to push out air and firm up the bond. Work out wrinkles by lifting and pulling before the sheet sets. Follow with a weighted roller or a walk-over.
Tip: Keep your boots clean and soft-soled. Adhesive on the sole sticks to the membrane and tears it.
Step 6: Repeat for the second half
Fold back the second half, apply adhesive to the deck and the underside as before, let it tack, and roll it in. The middle of the sheet needs the same care as the ends.
On roofs with multiple sheets, lay each sheet so the seams shed water, with the lap overlapping about 3 inches for splice tape, and leave the adhesive-free edge clean.
Step 7: Check for bubbles, wrinkles and open edges
Small air bubbles can be pressed out or cut, vented and pressed down with a patch. Wrinkles that have set are cut out and patched. Check that the adhesive extends to the edges and that the membrane is fully adhered at corners and changes of plane.
Next, make the seams with splice tape (see how to seam EPDM with seam tape) and flash corners, pipes and edges.
Water-Based Versus Solvent Adhesive
- Water-based: low odour, not flammable, cleans up with water, but slower to dry and sensitive to cold, humidity and freezing. Commonly not used below about 5 degrees Celsius.
- Solvent-based: faster open time and more forgiving of cool, damp days, but flammable and strong smelling, and it can damage foam insulation.
- Either way: follow the manufacturer's coverage rate, open time and temperature limits. Do not mix brands of adhesive and membrane without approval.
Working in Sections
On a larger roof, do not glue the whole sheet in one go. Divide it into sections you can coat, tack and roll in before the adhesive dries, and keep a dry line between them. Practice on a small area first to learn the open time on that day.
Fraser Valley Notes
Humid, cool days stretch open times, and morning dew is easy to miss. If the adhesive has not turned tacky in the time the data sheet allows, wait rather than rolling in wet adhesive. Rain on wet adhesive ruins the section, so keep an eye on the forecast and have tarps ready.
Common Mistakes
- Rolling in wet adhesive. It traps solvent or water and forms bubbles.
- Waiting too long. Adhesive that has dried hard will not grip, and the sheet peels.
- Stretching the sheet. It pulls back as it relaxes and lifts at edges and corners.
- Adhesive on the seam edge. Splice tape will not stick over adhesive, and the seam fails.
- No brooming. Trapped air becomes blisters that rise in the sun.
- Gluing in the cold or damp. The adhesive does not cure and the roof fails in the first wind.
When to Call a Professional
A fully adhered roof is possible on a small, simple, well-prepared deck, but the timing, the adhesive limits and the flashing details make it a job where experience counts. If the roof is large, has many penetrations or has an uncertain deck, call a roofer.
If an existing EPDM roof has bubbles, lifted edges or open seams, see how to repair an EPDM roof.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Flat Roofing and Torch On service or the towns we cover.
How to Install a Fully Adhered EPDM Roof: Questions
How do you glue down an EPDM roof?
Unroll and relax the sheet, fold half of it back, roll bonding adhesive onto the deck and the underside of the membrane, wait until it is tacky and does not stick to a dry finger, then roll the sheet into the adhesive without wrinkles and broom it flat. Repeat for the other half, keeping adhesive off the seam edge.
How long does EPDM adhesive need to dry before rolling in?
Usually 5 to 30 minutes, depending on temperature, humidity, wind and the product. The adhesive is ready when it is tacky but does not transfer to a dry knuckle. Cold, damp weather lengthens the open time, and hot sun shortens it. Check the open time and temperature limits on the manufacturer's data sheet.
Should you use water-based or solvent-based EPDM adhesive?
Water-based adhesive has low odour and is not flammable, but dries slowly and is sensitive to cold, humidity and freezing. Solvent-based adhesive has a faster, more forgiving open time in cool weather but is flammable, smells strongly and can damage foam insulation. The choice depends on the weather, the substrate and the manufacturer's approved products.
Why is my EPDM roof bubbling?
Bubbles form when adhesive was not tacky before the sheet was rolled in, when the sheet was not broomed to push out air, or when moisture or solvent was trapped. Sun heating trapped air makes them grow. Small bubbles can be vented and patched. Widespread bubbling points to gluing in poor conditions or a wet substrate.
Can you install EPDM in the rain?
No. Rain on the deck, wet adhesive or a wet membrane prevents the bond and leaves blisters. Even dew can spoil adhesive. Work only when the deck and membrane are dry, the temperature is within the adhesive limits, and no rain is expected before the adhesive has cured. Keep tarps on hand in the wet season.
Related Guides
All EPDM Rubber Roofing guides|The full How-To Library
This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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