Fabrication fundamentals: shop and field layout, forming, soldering, brazing, welding, fastening and sealants
Fabrication converts flat coil or sheet into watertight, dimensionally stable flashing. The exam tests layout math, bend allowance, joining method and fastener/sealant compatibility.
Shop and field fundamentals
- Lay out from a datum and account for bend allowance, material thickness and grain direction. Avoid sharp inside corners; use the manufacturer's minimum bend radius to prevent cracking, especially on zinc and coated steel.
- Form long pieces with a brake or roll former; keep bends uniform and avoid oil-canning. Cross-break large flats for stiffness.
- Solder copper after cleaning to bright metal, using compatible flux and enough heat for capillary flow. Remove flux residue. Do not solder aluminum or rely on ordinary solder for stainless; use brazing, welding or mechanical joints as specified.
- TIG welding suits stainless; copper can be brazed. Welded seams need back-purge or flux removal to prevent corrosion.
- Fasten with compatible screws, rivets or cleats. Sealant is a supplement, not a structural joint. Use neutral-cure sealant compatible with the metal and membrane.
Worked example
A 20-ft copper gravel stop is formed in one piece and fastened at both ends. At a 100°F temperature change, copper moves about 1/8 in. per 10 ft, or roughly 1/4 in. over 20 ft. If both ends are rigidly fixed with no slip or expansion joint, the metal buckles or tears fasteners. Detail one end fixed, the other with a slotted cleat or expansion joint, and keep fasteners out of the movement zone. For 20 ft, provide at least the calculated 1/4 in. movement allowance plus fabrication tolerance.
Traps
Using sealant to hide a poor lap; soldering dirty copper; mixing stainless with carbon-steel brushes; forgetting that factory coatings need touch-up; over-tightening fasteners and dimpling metal.