Loadbearing partitions

Concrete blockwork has largely superseded brickwork for reasons of economy and is, nowadays, probably the most common form of loadbearing partition. Dense concrete blocks offer the best sound insulation and are slightly cheaper than lightweight blocks. They are usually 100mm wide and will require a foundation or thickening of the slab, depending on the load they are carrying.

In order to maintain lateral stability of the partition, it is important to ensure that the blockwork is well bonded into any external or internal adjoining wall. The best method is shown in the diagram on the next page. Alternate courses of blockwork in the partition are bonded into the internal skin of the cavity wall.

An alternative method of providing lateral stability is to use wall ties or galvanised mesh. As the external wall is built, the bricklayers position the wall ties in line with the partitions, as shown in the diagram below. This method is inferior to bonding as it provides a much weaker joint. It is, however, suitable for non-loadbearing partitions.

A further means of tying walls together is to use a proprietary wall starter kit. This comprises vertical fixing plates of stainless steel or galvanised metal that are bolted to the receiving wall. The vertical plate has horizontal ties at right angles that secure the masonry at the end of the partition.

Concrete blocks are laid in a cement/sand mortar (often with a plasticiser added to aid curing) or cement/sand/lime mortar. A strong mortar, i.e. one with a high proportion of cement, should be avoided as it limits the ability of the partition to accommodate thermal and moisture movement, which may result in cracking. In addition, the concrete blockwork should be allowed to dry thoroughly before plastering takes place, as water absorbed by the blocks (from standing in the rain) causes slight expansion and plaster applied before the blocks have dried out will crack as the blocks slowly shrink. Where the partitions return at right angles, cut blocks are used to maintain the bond and where doors are to be incorporated, steel or concrete lintels are built in over the opening.

At first-floor level, the joists, which are supported by the partition, can either sit on top of the wall or be supported by joist hangers. In many cases, a loadbearing wall will continue up to the roof level to support part of the roof structure (if traditional roofing is used). In nineteenth- century and earlier buildings, a timber levelling plate (i.e. a wall-plate) was often built into the wall to support the upper floor joists. This is no longer done as problems of rot or insect attack may result in failure of the plate and subsequent failure of the wall above.