When installing a PVC membrane patch, the patch
material should be the same mil thickness, color and type as the existing
membrane.
Flashing: Flashing material should be the same mil
thickness, color and type as the existing flashing.
Bonding
adhesive: The bonding adhesive is produced with a nitrile PVC base and solvents
such as toluol and methyl ethyl ketone (MEK). Water-based bonding adhesives are
also available that use acrylic latex as a base
material.
Splice Cleaner: Cleaner is required at splice
areas where contaminants prohibit a proper weld of the membrane. The cleaner is
produced of napthinic solvents.
Repair
Procedures
The National Roofing Contractors Association (NRCA) and the
Single Ply Roofing Industry (SPRI) approve the following repair procedures when
installing a patch to return the membrane to a watertight
condition:
1. To promote thorough adhesion of a patch, it is essential
to begin preparing the surface by removing debris, contaminants and ballast
from the area of the membrane or flashing to be repaired. The area prepared
should extend beyond the perimeter of the patch to provide an ample-sized clean
work area.
2. Scrub the repair area with a solution of detergent and
water containing trisodium phosphate. Use warm water and a stiff-bristle brush
to scrub the membrane.
3. Rinse thoroughly with clean water and allow
the membrane to dry. A rubber-bladed squeegee and clean, absorbent, lint-free
cloths may be used to facilitate drying.
4. If the existing membrane
surface is excessively contaminated or degraded, carefully enlarge the hole
(make round) to allow the insertion of the new patch material under the
existing membrane so that welding of a patch may be accomplished to the
unexposed, less degraded side of the existing membrane.
5. Cut a patch
from a piece of new membrane material large enough to extend 4 inches beyond
any part of the defect. Round all corners of the patch to limit peeling of square
corners.
6. Round the ends of the defect in the existing
membrane.
7. Wipe the area of the existing membrane to receive the
patch and the underside of the patch material with a clean, absorbent,
lint-free cloth dampened with a solvent such as MEK or acetone. Do not pour the
solvent directly on the membrane. Wipe the area clean with the solvent-dampened
cloth.
8. Allow the surface of the membrane and patch to air dry.
9. Weld the patch in place by using the three-step thermoplastic
welding process: tack-weld, pre-weld and final-weld as described in the
following:
- Tack-weld the patch to the existing membrane by using a
hot-air welder to weld the membrane sufficiently to hold the patch in place
taking care to not wrinkle the patch material.
- Pre-weld the patch by
inserting the hot-air nozzle under the patch and forming a continuous pre-weld
approximately 2 inches from the edge of the patch. This pre-weld will prevent
heat leakage during the final welding and is achieved by following the welder
nozzle closely with a rubber-faced hand roller to provide pressure to adhere
the back of the weld area.
- Final-weld the outer 2 inches by
concentrating the heat on the remaining unadhered outer portion of the patch
until the membrane and patch have reached the welding temperature. The hot-air
welder should be moved quickly enough to avoid scorching the membrane, yet
slowly enough to achieve a complete weld. Immediately behind the welder, roll
the material to be bonded with the rubber-faced hand roller, rolling parallel
to the outside edge of the welder nozzle and pressing firmly to adhere and mate
the materials.
10. After the welded area has cooled, check seams for
voids with a rounded-tip probe such as a screwdriver or awl with the tip
rounded.
11. Where patches are made with reinforced membrane material,
seam seal the outer perimeter with seam sealant or caulking compatible with the
membrane. This will prevent water from wicking through the exposed edge of the
reinforcement.
12. If the ballast was removed, redistribute the
ballast over the exposed area.
