Sustainability of roofing systems requires that the systems be repairable. Any roof system can be punctured if the impact is great enough. Repair materials need to be compatible with the roof system in place; that, in turn, requires the building manager to know what’s overhead.
Commercial (low-slope) roof systems can be classified as:
- Bituminous built-up, using asphalt or coal tar pitch.
- Bituminous polymer-modified systems.
- Sprayed-in-place polyurethane foam with coating.
- Single-ply non-bituminous.
- Weldable thermoplastics.
- Non-weldable elastomeric.
- Metal roof systems.
Proper repair requires that you know what roof system is in place so that you use the appropriate materials.
BITUMINOUS BUILT-UP ROOFING SYSTEMS
The traditional built-up roof consists of multiple layers of bitumen-saturated roofing felts glued to one another with bitumen, with a “flood-coat” of more bitumen into which roofing aggregate has been embedded. Although less common, some built-up roof systems are surfaced with mineral cap sheets or just with paint-type coatings.
Asphalt is derived from petroleum as a heavy residual material (bottom of the barrel) (see Fig. 1). Note that “mineral spirits” is part of the same distillation process. Asphalt is completely compatible and soluble in this “paint thinner.”
When possible, repairs should be made with compatible materials. Asphalt mastic, found on every roofer’s truck, in lumberyards, and at roofing supply yards, is readily available. The ingredients will include petroleum asphalt, mineral spirits, fibers, and fillers. The flash point (the point at which the compound would ignite in the presence of a flame) is generally above 100 degrees F. (38 degrees C.), so the product isn’t designated “red label” or flammable.
For residential use, the mastic is packaged in 1-gallon pails. For commercial use, generally, more than 1 gallon is needed to effect repairs. In many cases, commercial roof mastic is provided in 2.5-gallon pails. Five-gallon pails are available everywhere; however, that’s a rather inconvenient size for a maintenance person to lug around a roof.
Thick or Thin?
Depending upon the proportion of ingredients, these “cut-back” products can be as thin as water (e.g. primer) or heavy enough that, even with a trowel, the products are stiff and require a strong arm to apply. (See Table 1 for a list of products.)
Some mastics have surfactants added that permit emergency repairs to be made even when the roof surface is damp (see photo 5). When weather improves, these patches should be checked and redone if needed.
After the patch is made, some loose aggregate from the surrounding area can be sprinkled into the topcoat of fresh mastic. Leaving the aggregate off has the advantage of keeping an eye on the repair to ascertain that it has succeeded, and to help you avoid stepping on a fresh patch.
Figure 2 lists common bituminous cutbacks and coatings.
Fig. 2: BITUMINOUS PRIMERS, COATINGS, MASTICS
- Mineral Spirits (Petroleum Distillate), ASTM D235
- Boiling Range 300-400°F
- Flash Point 100°F minimum
- Solution of mainly solvent with some asphalt ASTM D-41
- Also Coal-tar based primer ASTM D-43
Asphalt Roof Coating, solvent type
- Solution of asphalt in solvent (called cut-back)
- With asbestos fibers ASTM D-2823
- With fibers other than asbestos ASTM-4479
- Generally contain inert fillers as well
- With aluminum pigment for reflectivity and UV protection
- Non-fibrated ASTM D-2824 Type I
- Fibrated, but asbestos free ASTM D-2824 Type III
- Fibrated, may contain asbestos fibers ASTM D-2824 Type II
Asphalt Roof Mastic (Thicker than a coating, Trowel Grade)
- Solvent-based cutback, fibers and fillers*
- May contain asbestos fibers ASTM D-2822
- Asbestos free ASTM D-4586
- May be offered as Summer Grade and (thinner) Winter Grade
*Note, many mastic products may also contain polymers. To date, none have ASTM designations.
- Coal-tar roof cement
- May contain asbestos fibers ASTM D-4022
- Asbestos Free ASTM D-5643
Another useful maintenance material is based on emulsified asphalt. These products contain extremely fine particles of bentonite clay as an emulsifying agent. The colloidal nature of the emulsion stabilizes the cured coating so that it will not flow or crack the way asphalt films normally will. These products are termed “static.” These properties of asphalt emulsion are very helpful when a reflective coating is desired on a smooth-surfaced BUR or MB roof system since the white coating is less likely to disbond or crack as the substrate moves around (see photo 6). Since, by definition, emulsions contain water, reinforcing materials need to be permeable so that the water can escape while the coating sets up. Usually, woven mesh, polyester mat, or glass fiber ply sheet materials are used.
POLYMER-MODIFIED BITUMINOUS MATERIALS
These systems can be considered “high-performance” bituminous roofs. They generally consist of reinforcing, heavily coated with SBS or APP modified bitumen rather than ply sheets impregnated or only lightly coated with asphalt or coal tar bitumen as used in BUR systems. Reinforcements may be made of polyester or glass fibers, or combinations of both. Since the sheets have a continuous coating that was factory applied and are already waterproof, they don’t require field applications of hot asphalt. MB sheets can be identified in the field by noting their exposure. (Distance between visible laps.) Most, if not all, MB sheets are 1 meter wide, while BUR sheets are only 36 inches wide. MB sheets usually are just two plies, so exposed laps are a half-meter apart, while BUR laps will be 11 1/3 inches or 8.5 inches apart, indicating three or four overlapping ply sheets, respectively. BUR and MB may be repaired using MB materials.
MB grades include sheets than can be hot mopped (SBS sheets only), fused together using a torch, applied in solvent-based adhesives, or, in some cases, may be self-adhered by removal of a backer sheet. (For maintenance work, the torch-grades are desirable since the heat helps evaporate surface water and re-melts the substrate to embed dirt and/or loose roofing granules.) (See photo 7.) Like materials should be used for MB repairs (i.e. SBS MB sheets should be used for SBS repairs and APP MB sheets used for APP repairs). Asphalt primer is generally necessary with self-adhered, mastic, and hot-applied patches.
Since the use of a torch always involves some risk of fire, using self-adhered, peel-and-stick materials may be a safer option over some substrates (e.g. wood-fiber insulations). (The joint NRCA/ARMA/SPRI Repair Manual is a highly recommended resource. See photo 8.)
SPRAYED-IN-PLACE POLYURETHANE ROOF SYSTEMS (SPF)
These systems are generally coated with an elastomeric coating, as asphalt-based patches are too inelastic and brittle to apply over urethane foam. The general rule is to make a repair with the same generic category of coating or caulking as the existing roof; urethane repair material over urethane coatings, silicone patches over silicone, and acrylic over acrylic. For simple punctures, wiping the hole clean with a rag followed by a compatible caulk tooled in place will usually suffice.
As a general rule, single-ply membranes never should receive asphaltic patches. If you know the generic type of membrane, follow these procedures:
Thermoplastic material, such as TPO, PVC, KEE, and Hypalon® can be permanently repaired with a fresh piece of membrane heat welded to the cleaned roof surface. For emergency patches, duct tape applied to a dry surface will work until a contractor with appropriate tools and membrane can get there. If you have a lot of single-ply roofs in place, having an in-house employee approved (and trained) by the membrane manufacturer may keep warranties in place and water out. Self-adhering patches work well provided that the adjacent membrane is thoroughly cleaned, usually with detergent, and wiped dry.
Elastomeric membranes, such as EPDM, neoprene, or butyl should also never receive asphaltic patches. Again, emergency duct tape patches will hold for days or weeks; longer-lasting patches generally consist of a primer-cleaner, polymeric mastic, and a fresh piece of membrane. Here, too, self-adhering tapes will work well if compatible with the membrane. Some pre-made patching sheets are available with the adhesive tape already in place on the bottom side.
METAL ROOFING SYSTEMS
Various acrylic, butyl, and silicone caulking compounds are available that will perform well when protected by overlying the metal panels, such as at laps and penetrations. For rehab work, cleaning, applying a rust-inhibiting primer, a mastic or coating of recommended polymeric material, reinforcing mesh, and a top coating are appropriate. Preformed self-adhering tapes are a key component in new roof installations and may be used instead of pumpable caulking-grade materials. As with single-ply and SPF systems, repairs are best achieved when you have a roofing file that tells you what products you have in place and who the installer was. (See Chapter VII of the MBMA’s Metal Roofing Systems Design Manual for specific repair recommendations.)
Keep in mind that roof patches are temporary; roof repairs can be expected to last as long as the roof already in place.
RESOURCES ON ROOF PATCHES AND REPAIRS