Concave and convex is the term for two matching shapes: a concave (inward-curving, hollow) part and a convex (outward-curving, rounded) part that fits precisely into it. The concepts recur in many places in construction: in roof tiles, in mouldings and profiles, and in timber joints that interlock.
Where you find it
- Roof tiles — a concave and a convex tile (as with the monk-and-nun system) seal watertight against each other
- Mouldings — a hollow moulding (concave groove) and a convex profile (bead, ogee) together form an articulation
- Timber joints — a concave and a convex side can interlock, for example in a tongue-and-groove or a tongued joint
Application
The principle of concave and convex ensures good guidance and a tight fit: the concave part receives the convex part, so the parts cannot shift and water is drained away. When repairing old mouldings or old tiles it is important to match the exact concave and convex profile, otherwise the parts will not fit together.
Related terms
- Hollow moulding
- Ogee
- Tongue and groove
- Monk and nun
- Profile
- Moulding
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