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Carbonation

A natural process affecting the outer layer of concrete. Metal reinforcement within that layer is liable to early corrosion, with consequent fracturing of the concrete.

Cavity wall

Standard modern method of building external walls of houses comprising two leaves of brick or blockwork separated by a gap ("cavity") of about 50mm (2 inches).

Cavity wall insulation

Filling of wall cavities by one of various forms of insulation material:
Beads : Polystyrene beads pumped into the cavities. Will easily fall out if the wall is broken open for any reason.
Foam : Urea formaldehyde form, mixed on site, and pumped into the cavities where it sets. Can lead to problems of dampness and make replacement of wall-ties more difficult.
Rockwool : Inert mineral fibre pumped into the cavity.

Cavity wall-tie

Metal device bedded into the inner and outer leaves of cavity walls to strengthen the wall. Failure by corrosion can result in the wall becoming unstable — specialist replacement ties are then required.

Cesspool

A simple method of drain comprising a holding tank which needs frequent emptying. Not to be confused with Septic Tank.

Chipboard

Also referred to as "particle board". Chips of wood compressed and glued into sheet form. Cheap method of decking to flat roofs, floors and (with formica or melamine surface) furniture, especially kitchen units.

Collar

Horizontal timber member intended to restrain opposing roof slopes. Absence, removal or weakening can lead to Roof Spread.

Combination boiler

Modern form of gas boiler which activates on demand. With this form of boiler there is no need for water storage tanks, hot water cylinders etc..

Coping/Coping stone

Usually stone or concrete, laid on top of a wall as a decorative finish and to stop rainwater soaking into the wall.

Corbel

Projection of stone, brick, timber or metal jutting out from a wall to support a weight.

Cornice

Ornamental moulded projection around the top of a building or around the wall of a room just below the ceiling.

Coving

Curved junction between wall and ceiling or (rarely) between ceiling and floor.

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