What is a chimney coping slab?
A chimney coping slab, also called a chimney capping or chimney cap slab (Dutch: schoorsteenplaat), is a slab of concrete or natural stone, usually slightly sloped, on top of a chimney stack. It stops rainwater from soaking into the brickwork of the stack from above. The slab can shed water to one or more sides.
The slab may have openings for the flues, chimney pots or flue pipes. For open fireplaces, a slab without openings is also used, raised above the flue so the smoke can escape at the sides.
Types
- Overhanging: the slab projects slightly on all sides so that run-off does not stream down the brickwork. Ideally it has a drip groove on the underside.
- With a decorative edge: an edge under which a brick-on-edge course can be laid in the same brick as the stack, or a profiled concrete edge.
- Base slab: a similar slab can serve as a base on which a brick or prefabricated stack is built. This has no overhang.
- Material: concrete (often made to measure) or natural stone such as bluestone or basalt.
Application
Coping slabs are usually made to measure. Tips:
- Measure carefully: measure the outside of the stack at the top course and add the desired overhang on all sides.
- Openings: check the size and position of openings against the flue pipes, pots or any cowl.
- Fall: water should run off the slab, not towards the openings.
- Bedding: lay the slab on a full mortar bed and seal around pipes with heat-resistant sealant or a suitable collar.
- Working at height: the slab is heavy. Work from scaffolding or with safe roof access, never from a loose ladder.
- Inspection: replace a cracked or sunken slab promptly; water in a chimney causes frost damage and damp patches indoors.
Related Terms
- Chimney
- Chimney cowl
- Brick-on-edge facing course
- Chimney lead gutter
- Flashing
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