Large chase or duel

Change of loading Change of height

Control joints

Control joints

Fig. 2.12 Blockwork movement joints

mm joints are by volume:

cement/sand + plasticiser 1 : 5 to 1 : 6 masonry cement/sand 1 : 4 to 1 : 5

Below DPC level a stronger mix is required and sul-fate-resisting cement may be necessary depending upon soil conditions.

cement/sand 1 : 4

Where high-strength blockwork is required, stronger mortars may be necessary. Mortar joints should be slightly concave, rather than flush. Bucket-handle and weathered or struck joints are suitable for external use, but recessed joints should only be used internally. Coloured mortars should be ready-mixed or carefully gauged to prevent colour variations. Contraction joints should be finished with a bond breaker of polythene tape and flexible sealant. For expansion joints, a flexible filler is required, e.g. bitumen-impregnated fibreboard with a polythene foam strip and flexible sealant. Where blockwork is to be rendered, the mortar should be raked back to a depth of 10 mm for additional key.

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