Lead bossing is the craft technique of shaping flat sheet lead into three-dimensional forms by hammering it over a wooden pattern (called a former or bossing stick), without cutting or welding the material. It is one of the oldest and most durable methods of creating watertight junctions in roofing, particularly around chimneys, dormers, parapet walls, and other roof penetrations.
The Dutch term “bossing” is borrowed directly from English plumbing and roofing vocabulary, reflecting the shared craft traditions of Northern European leadwork.
Application
Lead bossing is used wherever sheet lead must conform to complex shapes on a roof:
- Chimney flashings: Lead is bossed into the angles where a chimney stack meets the roof slope, forming stepped or continuous soakers that shed water reliably.
- Dormer cheeks and valleys: The compound curves where dormer windows intersect the main roof require careful bossing to achieve a seamless, watertight skin.
- Parapet gutters: Lead linings in box gutters behind parapets are bossed into internal and external corners without introducing cuts that could later leak.
- Copings and cappings: Protective lead covers on wall tops are bossed over the edges to form drip details that throw water clear of the masonry face.
- Heritage restoration: Historic buildings with original leadwork often require bossing skills for sympathetic repair, as modern alternatives cannot match the lifespan or appearance of traditionally worked lead.
The process uses specialised tools including bossing sticks (hardwood mallets with flat or curved faces), bossing mallets, dressers, and setting-in sticks. The lead is worked cold, relying on its exceptional malleability. Skilled plumbers can stretch or compress the lead into position without thinning it excessively, preserving the sheet’s full thickness and therefore its longevity — which can exceed 100 years when properly installed.
Related terms
- Lead flashing
- Soaker
- Lead welding (lead burning)
- Roofing felt
- Zinc work
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