I want to attach a pull up bar to a wall. It's a brick wall that had plasterboard attached to it rather than rendered. When I drill into the wall there is approximately 10mm gap of empty space between the plasterboard and the wall. I suspect that the plasterboard will crumble if the pull up bar places pressure on it. I was hoping that there might be a way of flowing something into the gap between the wall and plasterboard using some thin flexibile tube to give the plasterboard some support. Something similar to expanding foam but it would have to be hard and solid when set. Is there any products you can suggest? I think that filling thw space within a radius of 100mm from the drill hole should be sufficient. I do not need to fill the space over the whole wall.