Am a DIY plasterer and have been replastering my lounge. I've blocked the old doorway off and have cut a new opening in the wall and installed the new door lining into this. I wanted to check the best method for filling the gap between the lining and the brickwork/wall. The old brickwork in the wall has crumbled away in places but the gap between the lining and the wall is around 10mm on average - with a few places where the corner of the brick has come away. I thought about using low expanding foam to get behind the lining and give it a good fix to the wall as well as filling the gap - then I would cover the foam in tape and then skim. Obviously the architrave will eventually cover all of this - I just wanted to check I could plaster over the foam?