Last month we looked at a couple of common roofing problems associated with bituminous roofing and how periodic patching could control them.
This column will focus on the newer single ply systems. Yes, they can have problems as well! Fortunately, effective repair techniques have been developed that can help address these problems and extend the working life of single-ply systems.
Usually black, commonly ballasted with large stones, EPDM roof membranes are very durable. Depending upon their age, there are a few problems that have been encountered.
In the earliest EPDM systems, wall flashings were composed of uncured neoprene, rather than cured (vulcanized) EPDM. The reasons for using the uncured material were logical. Wall flashings consist of changes in plane, with three planes intersecting at inside and outside corners. Cured elastomers are elastic, having a memory, and will snap back when the applicator tries to stretch or flair them to conform to walls, curbs or pipe penetrations. The idea was that the uncured material had no memory, and would stay put. It was intended that the material would gradually vulcanize with exposure to sunlight and heat. Unfortunately, the neoprene not only vulcanized, but continue to cross-link, becoming brittle. Stress cracks first appeared as very fine crazing, and eventually worsened until the flashing was as fragile as stale potato chips.
If the crazing was detected early, it was possible to 'save' the flashing by coating it with a reflective elastomeric coating, but eventually the material failed, coated or not.
The fix in this case was to remove the entire flashing system, to carefully clean and prime the adjacent EPDM membrane material so that a durable tie-in can be made, and replace the flashing with EPDM membrane material, not neoprene. In most cases, cured EPDM will be used, using premolded inside and outside corners when possible. The current EPDM membrane systems carry the membrane material itself up the wall, limiting uncured EPDM material and self-adhering tape to just the critical intersections.
Is this something that can be done in-house?
Well, if the roof is under warranty, the warranty will be applicable and should be invoked. However, many EPDM membranes are now well beyond the warranty period, and the number of EPDM suppliers has diminished. Additional considerations are the availability of repair membrane, primer, tape and adhesive. Unless you have had your personnel attend an applicator school, i.e., Carlisle or Firestone, it is probable that you are better off with an outside, 'approved' contractor.
Another, more recent problem with EPDM membranes has been shrinkage of the membrane itself, resulting in 'tenting' at terminations and wrinkling at drains and other penetrations.
The cause of the shrinking has never really been pinpointed, but the repairs are relatively straightforward. The joint NRCA/SPRI/ARMA Repair Manual for Low-Slope Membrane Roof Systems lists remedies for ballasted and for mechanically fastened systems. In general, the procedure is to cut the membrane free at terminations and permit it to shrink for an hour or so. New material is added to fill the gap and is sealed to the old, again paying a great deal of attention to surface preparation in order to achieve a durable tie-in. The manual suggests adding intentional folds in the membrane to accommodate future shrinkage. In new EPDM roof membrane design, reinforced EPDM perimeter strips are mechanically fastened to the substrate or wall, and blind-bonded to the roof membrane, providing restraint. This could be done in the repair sequence as well, as long as we have some way to fasten the reinforced perimeter strip to the deck or wall.
Seam separation in EPDM systems
EPDM seams can sometimes part, due either to application errors or failure of the adhesive itself. As with the uncured flashing problem, there have been a series of steps implemented over the years in order to improve seam durability. One was a change in surface cleaning techniques to include a combination cleaner/primer, another change from neoprene-based adhesives to butyl-based material, and most recently the introduction of self-adhering tapes. For some new, critical occupancy requirements, all field seams are double sealed by adding an additional batten strip of membrane over the sealed laps. These double-sealed membranes, generally combined with 90 mil rubber are eligible for longer-term warranties.
These new surface cleaning and double-sealing techniques also offer a useful way to repair or refurbish existing roof seams. In fact, many of the techniques used in new EPDM installations were originally developed as warranty repair methods for old EPDM roofs.
Attack by rooftop chemicals
EPDM rubber is very durable, but is vulnerable to attack by grease, animal fat, oils and petroleum solvents. Usually the areas that exhaust such materials onto a rooftop are localized. The best solution is to build a curb around these affected areas, making sure the curbed area has its own roof drains. The EPDM must be replaced with another material that resists such attack. Recommended materials include polyepichlorohydrin and neoprene. Some other single ply materials may also be suitable, but it is essential to check with the manufacturer first. You will have to define the concentration, temperature and nature of the contaminants in order to get the best recommendation.
The fasteners and stress plates used to attach thermal insulation and membranes are subject to back-out. This may be due to stripping the fastener out of the deck by over-torque during application, or by the repeated billowing of the membrane under wind load. If the fasteners are lifted and are puncturing the membrane, the membrane should be slit, the fastener (and stress plate if distorted) removed, and a new fastener installed (but not in the same deck hole). The slit area is then patched using the cleaning, priming and patching techniques mentioned above.
Repairing coated EPDM membranes
This is more complicated than it first appears. With the push for energy efficient roofs in hot climates, black membrane roofs are now frequently covered with energy-reflective white coatings. Surfacing EPDM with a white roof coating is becoming a vogue, but there are no clear instructions as to how to repair these coated membranes. If the coating is flaking off, it needs to be removed. However, EPDM membranes are quite thin, typically only 0.045 to 0.060 inches thick. Abrasion would be dangerous, as the tear resistance of the membrane drops dramatically when gouged or nicked. Chemical attack with xylol, toluol or gasoline works with uncoated EPDM, but the acrylic resins used in most white roof coatings are impervious to these solvents. If the white coating is chalking, i.e., turns a dark colored rag white, it is unlikely that a satisfactory bond will be possible. Scrubbing will remove the chalk, but now the danger is peeling the seams with the scrubbing tools. Hopefully the industry will give us some better guidelines soon. Recent field trials by the warranty service department of one major EPDM roofing manufacturer indicate that membrane repairs can be made directly over such coatings providing the coating was originally designed for compatibility with the membrane, and assuming the previously mentioned cleaning and surface priming procedures are followed. Once again, contacting the manufacturer is critical in order to verify if the existing coating was indeed designed for long-term compatibility with the membrane.
The roofing aggregate used on ballasted roofs is typically ¾ to 1-1/2 inches in diameter (#3 or #4 stone), applied at 10-12 lbs per square foot. The ballast may be displaced by wind scour or by billowing of the membrane. Scour typically appears as a heart-shaped pattern in the corners of the roof, where wind velocities are the highest. While replacing with the same ballast is easiest, it may be preferable to obtain larger stones (#1 or #2), applied at 20-25psf for 10-15 ft in from the roof edge. An alternative is to use 2 in. concrete pavers in the corners. The pavers should be freeze-thaw resistant, and be set over a non-woven fleece pad to prevent abrasion of the membrane. Detailed design data on ballasted roofs can be found in the ANSI/SPRI RP-4 document. SPRI can be reached at www.spri.org
Obtaining Repair Manuals: The joint NRCA/SPRI/ARMA Repair Manual for Low-Slope Membrane Roof Systems can be obtained by contacting NRCA at www.nrca.net In addition, several EPDM roofing manufacturers offer their own maintenance and repair manuals available for free download at their websites or via linkage from the EPDM Roofing Association (ERA) web site at www.epdmroofs.org
Next month we'll look at weldable single ply systems, their problems and repairs.