Part II of this series, we focus on advanced diagnostic techniques, evaluating repair options, and implementing long-term solutions that address the true cause of leaks.
Visual inspection of all exposed fasteners is recommended. Many fastener issues are obvious such as those that are missing, backed out, or not properly seated.
| Backed-out screw fastener | An aluminum rivet fastener that is not seated (tightly sealed) to the roof panel surface. |
The Wallace SealTester™ Tool is used to verify whether a fastener can hold a vacuum, proving that the fastener seal is airtight. If numerous fasteners are not seated flat to a metal panel or flashing surface, testing all the suspect fasteners may be time consuming. As an option, few test results can be extrapolated to similar suspect fasteners.
The rubber donut at the base of the tester (pressure gage end) is seated over the fastener head. The round knob handle on the opposite end is pulled until the lever drops into place, keeping the handle extended and maintaining the vacuum. The gage measures the vacuum pressure and any drop in pressure would indicate a potential leak at a fastener. If a fastener has been coated with sealant, the sealant may need to be removed for the rubber donut to seal around the flat surface adjacent to the fastener head – allowing for a good test result.
Many attempted topical sealant or coating repairs are a likely indication the roof has been leaking. Signs such as these are often indicators that the contractor sent to do the repairs never figured out the actual cause of the leak(s).
A topical coating repair traps moisture and causes accelerated rusting of the steel roof panels at the end lap joint. Once the coating is completely removed (depending on the severity of the rusting), the steel should be wire brushed, cleaned, and primed. Severely rusted steel (flaking rust) will require cutting out the severely rusted steel and replacement with new steel sheet metal.
| Moisture trapped under the coating caused steel corrosion. | Rust staining from steel corrosion under coating. |
Moisture trapped under the coating caused steel corrosion. Rust staining from steel corrosion under coating.
A single layer, liquid applied elastomeric coating is a very inexpensive potential solution to the leak. However, it must be determined whether the coating will correct the actual cause of the leak while not causing any new problems on the metal roof. Most elastomeric coatings are permeable, and if not completely adhered to the substrate, will allow moisture to be trapped. Note: Recoating over previous coatings and sealants is never recommended.
Since individual metal roof panels cannot leak, the sealant joint becomes a critical area for weathertightness. When “chasing leaks” the easiest course of action is to look for panel end laps, curbs, or pipe flashings around the reported leak(s). Unfortunately, repairs are often attempted with whatever coating or sealant has been brought to the site and will be spread on everything in the general vicinity. This is affecting a temporary repair and treating the symptom, not the actual “disease.” A good analogy is when the head gasket in an automobile engine is leaking; the recommended repair is to replace the gasket, not apply a topical coating. The typical problem with a metal roof is the sealant gasket and the only long-term fix is to replace or repair the gasket. If a metal roof is leaking, the most likely source of leaks is the gasket (butyl sealant) at the panel side lap seam, panel end lap seam, or roof penetration joint.
Repairing the actual cause of a roof leak does not take any more effort than properly applying a liquid coating. Simply remove a few fasteners, clean what can be accessed, apply a high-quality polyurethane sealant in the joint such as Vulkem, and install new fasteners. Vulkem, a moisture curing polyurethane sealant, can be successfully used on surfaces that have moisture present during application.
Slotted fastener holes at a roof panel end lap joint.
Depending on the joint, fastener holes should be checked for slotting. If you look at the seven holes in the panel end lap joint (above photo), you will see that the four original fastener holes are oversized, versus the three more recently added fastener holes. Oversized holes will make it difficult for a fastener to prevent movement between the two pieces of metal being joined together. Oversized (larger diameter) fasteners and large patch washers are a viable solution, as well as adding more fasteners. Large round and square EPDM backed metal washers are available from Dynamic Fastener to fit any fastener diameter.
Disassembling flashings or end laps is laborintensive but sometimes unavoidable. If recommending replacement or recover, evidence must be conclusive – especially since properly installed metal roofs can last 45+ years.
Poor sealant adhesion to the roof panels in an end lap joint.
The butyl tape sealant adhesion in this end lap joint (above photo) is very poor (minimal observed sealant webbing) and with the dirt in the sealant on the left side, is highly suspect as a source of leaks. Webbing occurs when the sealant has good adhesion to both metal surfaces and, when separated, the sealant looks like a spider web with sealant strings connecting both surfaces along the sealant joint.
The photo below shows a reassembled panel end lap joint. Some of the polyurethane sealant applied in the joint has squeezed out. Polyurethane sealant is UV stabilized (UV resistant) and will not deteriorate when exposed to UV light. Polyurethane sealants will form a protective skin while the underlying sealant remains flexible.
Repaired roof panel end lap joint.
Summary
Targeted sealant and fastener repairs can extend the life of a metal roof and delay costly replacement. However, widespread issues at end laps or penetrations can be expensive to address, and repair warranties are typically short (90 days to 2 years).
If repairs are the best solution, choosing the right contractor will be a key factor in properly completing repairs. When identifying a qualified pool of contractors to bid on your project, be sure to select only those firms with experience and expertise in installing low-slope metal roof systems. A contractor who is familiar with the materials and installation procedures for a new metal roof can and should be able to perform the proper repairs on that same existing metal roof. Remember, on a metal roof, core investigative tools include:
• Visual: Identify gaps and unseated fasteners
• Check: Inspect penetrations and flashings
• Probe: Confirm continuous sealant
• Test: Evaluate fastener airtightness
• Investigate: Disassemble joints as needed
The ultimate goal is to determine whether the waterproofing sealant gasket is present and functioning. Once confirmed, the most costeffective solution – repair or replacement – can be confidently recommended.
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by Ray Heisey, P.E., RRC, LEED AP