A white bedding coat followed the green primer; again, the contrast between the colors helped us get thorough coverage. The bedding coat secures the polyester reinforcing fabric to the metal substrate. The fabric comes in various widths and can be cut to any length needed. Generally, it's applied from the bottom of the roof up, in water-shedding order. However, since the finished application provides a complete, waterproof seal, that rule can be violated without risking leaks.
Complicated profiles require careful detailing, so the new and existing roof vent flashing and standing seams are treated first. The bedding coat is brushed over the primer, then the fabric is pressed onto the substrate, with care taken to eliminate trapped air bubbles. Once it's bedded down, the fabric is thoroughly saturated with another coat. The bedding coat is the heaviest applied and takes the longest to dry - it's not walkable for at least 12 hours. Drying time varies with weather conditions.
Two applications of top coat completed the installation. The top coats provided the final roof color, "Tinner's Red" in this case. In flat roof installations where foot traffic is anticipated, at least one additional coat - called "TrafficCoat," a more wear-resistant formulation - is applied. To work on this roof, the installer showed up with a rather ingenious custom-made system of 2x4 runners, nail-on brackets, and planks. By nesting the bottom end of the runners in the roof's box gutters and hooking their tops over the ridge, he made them easy to reposition as needed. Hydrostop applied to the underside of the runners helped protect the new roof coatings from scratches.
In a past treatment, the box gutters had been covered with an EPDM membrane that lapped up onto the metal roofing. With the use of CleanAct primer - available as part of the Hydrostop system - EPDM can also be coated with Hydrostop, which allowed us to restore and integrate the gutters once the main roof was completed.
New Roof: Mock Standing Seam
We had the false standing seams for the addition's roof - intended to help it blend with the older building - fabricated at a local sheet-metal shop. After applying the white base coat to the roof sheathing, the installers nailed the faux seams to the plywood on equal centers, imitating the original metal roof pattern. The sequence of fabric application and additional coats was identical to that used on the main roof. Since the addition was one story, its shed roof abutted the main building's brick sidewall. Usually in a case like this you would have to fabricate a reglet flashing and cut it into the brick. But because Hydrostop is self-flashing and bonds to masonry, we could simply apply the membrane directly to the face of the brick. The installers protected the brick above the installation line with masking tape, providing a neat finished appearance.
As a final touch, we installed copper gutter at the eaves. These extra expenses - the false seams and the copper gutter - brought the total cost of the addition roof to about $9.80 per square foot. That's still a pretty good price for creating such a close match to the original roof.
Steve Thompson owns Full Spectrum Construction, in Louisville, Ky.