Water Blisters Under Roof Membrane

Vapour from contact bonding adhesive.

Water blisters under roof membrane.

Blisters range in size from a penny to entire roof deck areas and can contain significant quantities of water. Water leakage into the interior has resulted when the blisters expand to a crack or joint in the concrete slab. The rv manufacturer simply didn t apply the adhesive evenly or left some dirt on the roof that the adhesive couldn t stick to. The roofer did not completely cover every square inch of the roof deck with adhesive as he re roofed.

What is a roof blister. If the membrane is not weathered or cracked repairs are typically not required. As blisters extend over cracks or joints in the concrete water can leak to the interior. They occur when a gas usually water vapor is trapped within the roofing system either between the plies or between the plies and the insulation.

Bonding of the membrane to the substrate is of concern at perimeter areas particularly at low profile edges to eliminate probability of roof blow offs. They appear in all types of roofing systems residential and commercial. In time the bubbles will decrease as the membrane is partly breathable. Bubble like or long thin raised areas on the roof are called blisters.

Blisters form when there are pockets of air or moisture trapped between layers of your roof s membrane or between the membrane and the roof deck. However water filled blisters under these membranes have been discovered on numerous buildings in the pacific northwest in recent years. Flat roof blisterts bubbles occur as the direct result of hot air that rises from the crawl space between the top floor ceiling and the roof deck of the home. Roof systems with membranes are more prone to blistering because blisters are formed by gaps between the membrane plies or between the underlying substrate and the membrane.

Blisters on adhered single ply membrane systems are typically caused by lack of adhesion at the point of application. This area can fill up with air or water to form a blister which looks like a. In several cases the blisters were so large that replacement of the membrane was required. When the rubber membrane is bonded too quickly and prior to the adhesive drying bubbles will appear under the membrane caused by the trapped vapour from the adhesive.

Blisters are the most common roofing problem. As the sun heats the roof those pockets expand and stretch the membrane. In severe cases the membrane will crack when the pressure becomes too great. In the most severe cases the membrane may need to be peeled back and re bonded.

Bubbles can also be caused by water getting under the membrane which shouldn t happen with a good installation but may happen if any of the seams develop holes. In some cases large blisters 2 deep have displaced concrete pavers creating hazardous walking conditions. There are four main reasons why blisters bubbles occur on your flat roof. Roof blisters are not limited to one type of roof system.

The most common cause of roof bubbling is poor installation of the roof.