Whilst bubbles or blisters on a one-piece EPDM roof can be unsightly they will not cause the rubber membrane to fail. These bubbles of trapped air/moisture can be caused by a variety of issues which are all avoidable if the roof design is correct and the membrane is correctly installed.
Vapour from Contact Bonding Adhesive
Contact bonding adhesive is used for bonding the rubber membrane on upstands and around the perimeter of the roof deck. The adhesive is solvent based and must be allowed to gas off and become touch dry prior to bonding the membrane into position. If the rubber is bonded prior to the adhesive drying then bubbles will appear under the membrane caused by the trapped vapour from the adhesive.
These bubbles are often not severe and will disappear over a relatively short period of time as the EPDM membrane is partially breathable. The process can often be accelerated by weighting the affected area. In severe cases where the adhesive has not been allowed to become touch dry the membrane may need to be peeled back and re-bonded.
Expanding Trapped Air Within The Roof Structure
This type of bubbling / lifting can occurr on warm deck roof designs where the EPDM membrane is fully bonded onto either a timber deck or directly onto the insulation. If the roof structure under the insulation is damp or the boards are fitted with large gaps the trapped moist air will expand when the sun warms the roof and appear along the seams in the boards. Often the membrane will contract back in to position in the evening when the roof cools back down .
It is important when installing the warm deck insulation to ensure the roof structure underneath is dry and that the insulation boards are fitted snuggly together. Any gaps can be filled with an expanding foam adhesive to stop the trapped air lifting the membrane. If you are installing a timber deck over the insulation a cheap visqueen membrane can be installed under the timber deck, this is also a great way of ensuring that the expanding air doesnt cuase the membrane to lift.