The cause of a loose socket has been traced to loose bricks (or their remains). The socket pattress was held loosely in by plaster around its edges.

As the fragments of brick were doing nothing more than sitting on the cavity wall foam I have removed them.

I now have a rather intimindating void to fill.

Do I (a) re-fill the hole with brick that must be shaped to fill the hole, (b) ditto but with easily shaped lightweight block rather than brick or (c) contrive suitable shuttering and fill the hole with concrete.

A and B are least appealing because of the difficulty of properly filling the crevices with mortar when pointing in the new brick(s) and the difficulty of cutting them to fit. C is most appealing because of its gap filling properties.

TIA

Richard