Extension brickwork - join to original?

crowthers

What you have to take into account is that any new brickwork is likely to settle at a different rate to old work. Some old brickwork was laid usinig a lime based mortar which allowed flexibility for some settlement throughout its life. But assuming that the old brickwork was laid using a sand cement mortar it will have settled over time and is unlikely to move again unless the foundations are inadequate or very dry weather causes the soil to move. (Both unlikely)
However the new brickwork and foundation will settle a little, and even a few millimetres will cause a crack to appear if you have toothed the work in. You could of course keep making good this cracking by repointing the joint over time. The preferred solution is to use a crocodile/furfix fixing solution which will allow the new leaf of brickwork to move relative to the old. The visible joint between the two brickwork leafs should then be filled with a flexible jointing compound in a colour to suit the brickwork. Another solution is to hide the join behind a rainwater downpipe. Finally if you rendered over the joint it would definitely show cracking in th enear future.