Tying in New Junction Walls to Existing Walls

Again, when constructing extensions or making internal alterations, there is often a need to tie in a new wall at a 90-degree angle to an existing wall, in the form of a junction wall. Toothing-in and block bonding (see above) can be used for this purpose – the only essential difference is that the indents have to be cut into the face of the existing wall in order to tie in the new junction wall.

The first task is to mark out accurately on the existing wall the positions of the toothings or block indents to be cut out. When marking out, allow for an indent that is 25mm wider than the brick or block to be let in and take care to ensure that the indents are all vertically aligned. Having marked out the indents, the cutting process will be greatly aided by drilling and removing as much as possible of the mortar joints adjacent to the brickwork being removed (indicated by the solid red marking-out line). Where broken marking-out lines cross through bricks, these are the points at which bricks must be firmly marked with a hammer and sharp bolster chisel. This process will ensure a neat edge to the indent when chopping out is complete, which is most important when the finished work will be visible, such as when cutting toothings on facing work.

Tying in New Junction Walls to Existing Walls

Fig. 274 Marking out the face of an existing wall for toothing in or block bonding a new junction wall.

When chopping out an indent, start from the middle using a lump hammer and sharp cold chisel and work outwards, taking care not to damage the adjacent bricks when the
outside edges of the indent are reached. Working from the outside in to the middle will result in damage to the bricks that surround the indent. When a clean edge has been achieved in the middle of the indent, it is then possible to continue chopping out with a narrow, sharp bolster instead of the cold chisel.

Tying in New Junction Walls to Existing Walls

Fig. 275 Method of chopping out indents for toothing or block bonding.