Case 1

Remedial

Where blistering is caused by water vapour, and is confined, install vapour vents so as to release the water vapour pressure underneath the roof coverings. However, these will have a limited effect where the first layer is bonded to the roof deck. If blistering occur throughout the roof surface area, it is advisable to relay the membrane.

Repairing Blisters

Begin patching a blister by first cutting across its face with a sharp utility knife. Once the blister has been opened, check the inside to make sure that there is no water present. If water is present, make sure the area must be dried, either by leaving the blister open and letting the sun dry the area or by using a portable hair dryer.

When the area is completely dry, use a small putty knife to force roofing cement under both sides of the cut. Next, press the cut edges of the blister down into the roofing cement until they lie flat. Then apply a good coat of roofing cement over the top of the cut. Before this dries, cut a patch (from rolled roofing material) large enough to extend 2 inches beyond the orginal cut.

Press this patch down into the roofing cement and nail it into place, spacing the nail about 2 inches apart. The last step is to cover all of the exposed nailheads with a coat of roofing cement. Some professional roofers will also give the edges of the patch an additional coat of the cement.