Polymer modified bitumen membranes are asphalt based and are typically installed with one or more base or underlying sheets and a cap sheet. Modified bitumen cap sheets are typically either smooth surfaced, granule surfaced, or foil-faced or they may be field surfaced with a coating or a flood coat of asphalt and aggregate.

This section contains generic repair procedures for polymer modified bitumen membranes. Included in this general category are the following types of modified bitumen membranes:

• Styrene-butadiene-styrene (SBS)
• Atactic polypropylene (APP)

SBS and APP modified products may have slightly different repair procedures.

Typical SBS Membrane Repair Procedure

The following repairs are utilized in several different repair situations which require installing a patch to return the membrane to a water-tight condition.

• If water leakage has occurred, open the membrane and inspect the insulation, vapour retarder, and deck for damage. Remove and replace wet or damaged insulation, vapour retarder and/or roof deck as required.
• It is essential to prepare the surface. Remove debris, contaminants, surfacing, ballast or loose granules from the surface of the membrane or flashing to be repaired.
• The area to be prepared should extend beyond the perimeter of the patch to provide a suitable work area on which to install the patch. Clean the surface of the membrane with a stiff broom to remove any loose granules.
• Embed the granules on granular surfaced cap sheets for the entire area of smaller repairs and for 150 mm (6 in) minimum at the perimeters of larger repair areas and prime the remainder of the repair areas with compatible modified bitumen primer.
• Cut a base sheet patch of like material 150 mm (6 in) minimum larger in all dimensions than the defect to be repaired. Clip, or round the corners of the patch. Install the patch in hot asphalt, cold adhesive or by heat welding in accordance with the membrane manufacturer’s requirements. When using hot asphalt as the method of application, use Type 3 asphalt and take care to maintain the asphalt at a minimum of 204°C (400ºF) at the point of application. When torching, work gradually, applying heat only sufficient to achieve adhesion without damaging the membrane reinforcement or scorching surrounding membrane.
• Apply moderate pressure to the patch to assure adhesion of the base sheet patch to the existing membrane.
• Cut a cap sheet patch of like material 150 mm (6 in) minimum larger than the base sheet patch. Note that the cap sheet patch is often cut to cover the full width of the cap sheet exposure (typically 900 mm (36 in)) and minimum 150 mm (6 in) longer than the base sheet repair in each direction in order to minimize the visual appearance of a patch. Round the patch corners slightly. Install the patch in hot asphalt, cold adhesive or by heat welding in accordance with the membrane manufacturer’s requirements.
• Apply loose granules to the edges of the repair area as required. Embed granules in hot asphalt (Type 3), or heat surface of the membrane area until asphalt turns liquid and embed granules.

Typical APP Membrane Repair Procedure

The repair of APP modified bitumen roof membranes is essentially similar to the repair of SBS modified bitumen membrane with the exception that APP membranes cannot be adhered with hot applied asphalt bitumen; only appropriate cold adhesives or torch application techniques may be used for the adhesion and sealing of APP modified bitumen roof membrane systems and system repairs.

• If water leakage has occurred, open the membrane and inspect the insulation, vapour retarder, and deck for damage. Remove and replace wet or damaged insulation, vapour retarder and/or roof deck as required.
• It is essential to prepare the surface by removing debris, contaminants, surfacing or ballast from the surface of the membrane or flashing to be repaired. The area to be prepared should extend beyond the perimeter of the patch to provide a suitable work area on which to install the patch.
• Clean the surface of the membrane. If the membrane surface has been covered with a protective surfacing, remove the surfacing in the repair area, embed granules if appropriate.
• Lightly prime the surface of the membrane with asphalt primer and allow to dry.
• Cut a base sheet patch of like material 150 mm (6 in) minimum larger in all dimensions than the defect to be repaired. Clip, or round the corners of the patch. Install the patch in cold adhesive or by heat welding in accordance with the membrane manufacturer’s requirements. When torching, work gradually, applying heat only sufficient to achieve adhesion without damaging the membrane reinforcement or scorching surrounding membrane.
• Apply moderate pressure to the patch to assure adhesion of the base sheet membrane patch to the existing membrane.
• Cut a cap sheet patch of like material 150 mm (6 in) minimum larger than the base sheet patch. Note that the cap sheet patch is often cut to cover the full width of the cap sheet exposure [typically 900 mm (36 in)] and minimum 150 mm (6 in) longer than the base sheet repair in each direction in order to minimize the visual appearance of a patch. Round the patch corners slightly. Install the patch in cold adhesive or by heat welding in accordance with the membrane manufacturer’s requirements.
• Apply membrane surfacing to match the existing in accordance with the membrane manufacturers written instructions.

Ridges & Buckles

Generally, ridges and buckles on these materials, if not cracking, are not problems that need to be repaired. Unless the ridge is in a traffic area or if the membrane is cracking, it is best to leave this condition alone and monitor the area.

• If the membrane is creased, cracked or damaged,  then  repair  is required. If repair  is needed, first inspect for water that may have leaked into the roof system. If water leakage has occurred, open the membrane and inspect the insulation and deck for damage. Remove and replace wet or damaged insulation, vapour retarder and/or roof deck as required.
• Cut the ridge or buckle down the center to lay the material flat. Prior to installing the patch, open the ridge or buckle and re-adhere the unbonded portions using appropriate adhesive or by carefully heating the underside with a torch.

Complete the repair using the appropriate Typical SBS or APP Membrane Repair Procedure as described above.

Laps and Splices

Problems encountered at the lap of modified bitumen membranes are usually fish mouths (open wrinkles at the edge of the lap) or voids (unbonded areas in the lap). The repair procedure is the same for these two types of defects.

• Remove dirt and debris and inspect for water leakage. If water leakage has occurred, open the membrane and inspect the insulation and deck for damage. Remove and replace wet or damaged insulation, vapour retarder and/ repair or roof deck as required.
• Carefully cut the void or fishmouth with a sharp hook-bladed utility knife to lay the unbonded portion flat. Prior to installing the patch, re-adhere the unbonded portions using appropriate adhesive or by carefully heating the underside with a torch.

Complete the repair using the appropriate Typical SBS or APP Membrane Repair Procedure as described above.