Laying of Arch

Skewbacks at the springing of the arch are prepared first and placed very carefully in the correct angles. Voussoirs are then laid on either side of the crown. In case of brick arch, bricks may be placed as showing stretcher-face or header-face. More than one ring may be used. Joints are to be filled with mortar not less than 5 mm and not more than 15 mm thick. Finally the key stone is fitted in to lock the whole arch in position. In order to counteract the thrust, the masonry above the skewback at the haunches should be loaded by filling up the spandrels up to the level of the crown of the arch or at least two-thirds of the height of the arch. This has to be done on both sides of the arch. Before hardening of the mortar, the centring is slightly slackened by means of easing the wedges thereby permitting the voussoirs to rest on their beds properly. The skewback is kept wet during the work. The above procedure is followed for stone and brick arches. For concrete arches the procedure followed for lintels may be followed.