Bubbles or wrinkles in a newly laid EPDM roof can be alarming. Some are temporary surface changes that settle as the membrane relaxes; others point to trapped solvent, uneven adhesive coverage or a detail that needs attention before it becomes a weak point.
The important thing is not to treat every raised area in the same way. Its position, shape, behaviour and relationship to seams, edges and penetrations all matter. This guide explains what to check, what may settle naturally and when the safest course is to stop and investigate.
What is the difference between a bubble, blister and wrinkle?
The terms are often used interchangeably on site, but they can describe different conditions:
- A bubble or blister is a rounded raised area where the membrane is not sitting against the deck. It may contain air, moisture or solvent vapour.
- A wrinkle is a fold or ridge in the sheet, commonly caused by the membrane not being allowed to relax, uneven laying or movement while it was being bonded.
- A tented seam or detail is a raised area at a lap, corner, upstand or termination. Because it affects a waterproofing junction, it deserves more urgent attention than a small isolated surface ripple.
A neat-looking roof is desirable, but appearance alone does not establish whether the waterproofing has failed. Start by locating the raised area and checking whether it crosses a seam, tape edge, corner or penetration.
Why do bubbles form under EPDM?
Adhesive laid too wet
Many EPDM bonding adhesives need time to flash off before the membrane is brought into contact with the prepared surface. If the sheet is laid while the adhesive is still too wet, evaporating solvent or moisture may become trapped beneath it and create bubbles.
Flash-off is not governed by the clock alone. Temperature, humidity, airflow, substrate condition and the amount of adhesive applied all affect the result. Always follow the instructions for the exact adhesive and membrane system being installed.
Too much, too little or uneven adhesive
Heavy pools of adhesive take longer to dry, while missed or thin areas may not form a reliable bond. Both can leave visible high and low spots. Use the manufacturer’s stated coverage rate and the recommended roller or application tool rather than trying to judge the quantity by colour alone.
For a clearer breakdown of where different adhesives should be used, read EPDM Adhesives Explained: Which Adhesive Do You Need?
A damp or contaminated deck
EPDM should not be bonded over a deck that is damp, dusty, greasy, frost-covered or otherwise unsuitable for adhesion. Moisture trapped in the build-up can expand as the roof warms. Dust and debris can also prevent full contact between the membrane and substrate.
Before work begins, the deck should be sound, dry, clean and compatible with the specified system. Fixings, board joints and surface irregularities should be dealt with before the sheet is unfolded.
The membrane was not allowed to relax
EPDM can retain folds and tension after storage and handling. Once positioned, the sheet normally needs to lie flat and relax in accordance with the manufacturer’s instructions before bonding starts. Rushing this stage can lock creases into the finished roof.
Changing weather conditions
A roof that looks flat in cool conditions may show raised areas when direct sun warms the black membrane and the air or vapour beneath it expands. Low temperatures can also slow adhesive flash-off and make uncured detailing materials less workable.
Do not assume that yesterday’s drying time will suit today’s conditions. Check the weather window, product temperature limits and surface condition immediately before application.
Will EPDM bubbles disappear on their own?
Some small, soft bubbles caused by temporary vapour movement may reduce as conditions stabilise. Minor storage creases can also relax. However, there is no safe rule that every bubble will disappear, and a persistent raised area may indicate incomplete adhesion.
Monitor the area rather than guessing:
- Photograph it from the same position in cool and warm conditions.
- Note whether it becomes larger in sunlight and contracts later.
- Check whether the perimeter remains fully bonded.
- Look for movement towards a seam, edge, outlet or rooflight.
- Inspect internally for any sign of moisture, staining or deck movement.
If the area is large, worsening, hard-edged, close to a waterproofing detail or accompanied by a leak, obtain system-specific technical advice.
Should you puncture an EPDM bubble?
Do not puncture or slice a bubble simply to release the air. Piercing an intact membrane creates a deliberate route for water and turns a diagnostic question into a repair. Pressing, injecting adhesive or applying a patch without first identifying the cause can also trap moisture or conceal a wider adhesion problem.
If an opening is genuinely required as part of an approved repair, it should be completed using the correct cleaning, priming, flashing or cover material for that membrane system, with the repair extending onto sound, properly prepared EPDM. Follow the manufacturer’s detail or refer the work to an experienced installer.
When does a wrinkle need attention?
A shallow ripple in the middle of an otherwise fully adhered sheet is different from a wrinkle that runs into a seam or corner. Escalate the inspection when a wrinkle:
- passes beneath seam tape or a cover strip;
- creates a channel into a corner or upstand;
- prevents a termination from lying flat;
- has a sharp fold that is under repeated movement;
- collects water or debris against a lap;
- can be lifted easily from the deck; or
- changes noticeably over time.
Details carry more risk because tape and flashing rely on continuous contact. Voids, fishmouths and bridging at a change of angle can interrupt that contact even when the main field membrane remains watertight.
A practical inspection checklist
- Identify the location. Mark whether the issue is in the field sheet, a seam, corner, edge or penetration.
- Check the roof is dry. Do not diagnose adhesion by pressing water towards a questionable detail.
- Inspect the perimeter. Look for open tape edges, fishmouths, lifted trims or loose terminations.
- Compare temperatures. Observe the area during cooler and warmer parts of the day.
- Review the installation conditions. Consider deck moisture, adhesive coverage, flash-off time and whether the membrane was allowed to relax.
- Check the product instructions. Different water-based, solvent-based and polyurethane products are not interchangeable.
- Record rather than disturb. Take photographs and measurements before attempting any repair.
How to prevent bubbles and wrinkles during installation
Plan the weather window
Allow enough dry time not only to place the sheet but also to complete edges, corners and penetrations. Do not start solely because rain has stopped; the deck and application conditions must still meet the product requirements.
Prepare the substrate properly
Check that boards are dry, securely fixed and free from raised fasteners, dust, sharp debris and contamination. Correct low or moving boards before covering them. Membrane should not be used to disguise defects in the deck.
Dry-position the complete sheet
Unfold and align the EPDM without stretching it. Confirm the required overhangs and coverage around every upstand before adhesive is opened, then allow the sheet to relax for the period stated by the manufacturer.
Apply adhesive consistently
Work at a controlled pace and maintain an even coat at the specified coverage. Keep adhesive out of areas reserved for primers and tapes. Observe the required flash-off test rather than relying on a fixed number of minutes.
Lay the membrane progressively
Bring the membrane into contact smoothly without trapping folds. Sweep or roll it using the recommended technique, working in a direction that allows air to escape instead of enclosing it.
Inspect before completing the details
Check the field sheet while there is still safe access to the full roof. Pay particular attention before closing seams or fixing edge trims, because a wrinkle running into a detail is harder to correct later.
Repair or monitor: a simple decision guide
| What you find | Suggested next step |
|---|---|
| Small isolated soft bubble in the field sheet, no leak and stable edges | Record and monitor; consult the membrane guidance before disturbing it |
| Minor relaxed storage crease away from details | Observe through normal temperature changes |
| Large or growing area of poor adhesion | Investigate the installation conditions and obtain technical advice |
| Wrinkle, fishmouth or void entering a seam or corner | Treat as a detailing defect requiring prompt assessment |
| Lifted tape edge, puncture or active leak | Keep the area dry and complete a system-compatible repair |
| Soft or moving deck beneath the membrane | Investigate the roof build-up; a surface patch alone may not address the cause |
Frequently asked questions
Are bubbles in a new EPDM roof normal?
They are not automatically evidence of a leak, but neither should they be dismissed without inspection. Their size, cause and position determine the risk.
Can I glue an EPDM bubble back down?
Not safely without identifying what is inside it and confirming an approved repair method. Introducing incompatible adhesive or trapping moisture may make matters worse.
Why do bubbles appear when the sun comes out?
Warmth can expand trapped air or vapour and make an area of incomplete adhesion more visible. The change is useful diagnostic information, but it does not identify the cause by itself.
Do wrinkles always cause leaks?
No. A minor field-sheet ripple may remain watertight. A wrinkle that crosses a seam, flashing, edge or change of angle is more concerning because it can interrupt continuous adhesion.
What should I order for an EPDM repair?
The correct materials depend on the membrane system and the type of defect. A typical detail may require compatible cleaner, primer, tape or flashing and a seam roller, but products should be selected from the manufacturer’s approved repair detail. Avoid mixing systems merely because two products are both described as EPDM accessories.
Get the whole EPDM system right before arriving on site
Many membrane problems begin with a missing accessory, unsuitable adhesive or a rushed change of plan. Confirm the membrane, deck adhesive, contact adhesive, primer, tapes, trims and application tools as one compatible system before work starts.
If you are still specifying the roof, begin with How to Choose the Right EPDM System for Your Flat Roof. For quantities, use How Much EPDM Membrane Do I Need? and allow separately for every upstand, edge and detail.
This guide provides general installation information. Always follow the current instructions for the membrane and accessories being used, together with the requirements of the roof design and applicable regulations.
