In a material contract all materials and labour required for the construction are supplied by the contractor
In a labour contract, all the materials are supplied by the owner and contractor is responsible for providing labour including supplying tools and plans, equipment, shuttering, scaffolding etc
Centring is a type of falsework: the temporary structure upon which the stones of an arch or vault are laid during construction. Until the keystone is inserted an arch has no strength and needs the centring to keep the voussoirs in their correct relative positions.