Thin-joint blockwork may be constructed with mortar joints of only 2–3 mm, provided that the aircrete or equivalent blocks have been manufactured to fine tolerances and on-site workmanship is good. The special rapid-setting mortar sets typically within 60 minutes and the full bond strength is achieved after only two hours, allowing more courses to be laid each day. In the case of brick and block cavity construction, the inner leaf is built first, providing a weatherproof enclosure as quickly as possible. The outer skin of brickwork can subsequently be built up, using wall ties fixed to the face, either screwed or hammered into the completed blockwork. Bed joints in thin-layer mortar blockwork do not necessarily coordinate with those of the brickwork, so conventional cavity wall ties can only be used if they are slope-tolerant.
Usually, inner leaf construction commences with a line of 440 X 215 mm standard-height blocks, with normal bedding mortar to compensate for variations in the foundation level, followed by the larger 440 or 620 mm X 430 mm-high blocks, which should weigh less that 20 kg for repeated lifting by one operative. Heavier blocks require mechanical lifting or two-person handling. Thin-joint mortars, consisting of polymer-modified 1 : 2 cement : sand mix with water-retaining and workability admixtures, are factory
pre-mixed and require only the addition of water, prefer ably mixed in with an electrically powered plasterer’s whisk. The mortar is applied with a proprietary appli cator of the appropriate width or through a pumped system to achieve a uniform thickness of typically 2 mm. Work should only proceed at temperatures above 5°C.