Flat Roofing Specialist! Commercial Low-Slope Systems

Flat Roofer Association

January 24th, 2012 at 12:37 pm

BUR Blisters – Remove, Patch, or Monitor

Built-up Roof Blisters

Flat Roofing Repairs – Built-up Roofing Membrane

Blisters may need to be repaired if

  • The blisters occur in areas of high traffic
  • Membrane deterioration
  • Excessive loss of surfacing (gravel)
  • Blisters in laps which have reduced lap coverage
  • Blisters have breaks, or cracking

Whether to remove, patch, or monitor blisters is a judgment call. Blisters that are keeping air in will keep water out, if this is the case it may be preferable to leave the blisters undisturbed. Should it be determined that blister removal is necessary, the following steps should be used.

  1. Remove all loose debris from the surface of the membrane or flashing to be repaired. The area should extend a minimum of 18 inches beyond the perimeter of the defect.
  2. If membrane surface has been flood coated and aggregate embedded, carefully spud the aggregate free from the surface and sweep clean.
  3. Carefully cut and remove the blistered material until good adhesion of the membrane is reached.
  4. Inspect insulation or deck for damage caused by water infiltration. Remove wet or damaged insulation and repair or replace as required. Properly attach or adhere new, dry insulation (consistent with the thickness of the existing insulation).
  5. Prime the surface of the BUR membrane with asphalt primer. Be sure not to overuse the primer, because it may harm the existing membrane and inhibit adhesion of newly applied membrane.
  6. Install the same number of plies as were removed in cold-applied adhesive or hot bitumen. Extend the bottom ply at least 6 inches beyond the area to be repaired and each exceeding ply at least three inches beyond the previous ply.
  7. Reapply the surfacing. For small repair areas, it is a common practice to apply the coating immediately after the membrane repair is made.
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