Plasterboard Fixing Failure at Window Reveal

[Spinny]

Could do with some suggestions on how to fix a problem boarding up a window reveal.

 

The window is 2.4m high running up from floor level. The window has been fixed to the inside of the outside blockwork leaf so that the inside frame is level with the inside edge of the outer leaf. It is an unusual detail as we had the architect remove the inner blockwork leaf so we could have a narrower window reveal. Hence there is no conventional cavity closer. In insulating and boarding the area we decided to fix some 30mm XPS to the inside of the outer block and then also fix the reveal board to this. So we used resin to fix the XPS to the concrete block and resin to fix the plasterboard to the orthogonal edge of the XPS. We used the XPS as it is a good insulator, rather than fix a strip of timber against the outside leaf.

 

The plaster board fixing to the XPS has just failed. And so has the XPS fixing to the concrete block. What seems to have happened with the plasterboard resin fixing is that XPS itself has failed in tension so the resin is still stuck to the board along with a thin layer of the XPS. What seems to have happened with the XPS resin fixing to the concrete blockwork is that it has failed to bond well to the blockwork possibly not helped by some mortar residue on the block.

 

Now the problem is how can we redo this reveal to get secure fixings ?

(Especially since the front face has now been insulated and boarded limiting options.)

 

See the attached pics...

 

 

 

 

[crispy_wafer]

Ooh, now…. Wait for the experts to appear, but my initial thoughts would be bonding 25mm angle to the frame top to bottom and using this to fit the reveal board to.

[Spinny]

The pencil line shows the chosen plaster line to be achieved, so the plaster board edge will cover the edge of the frame and the 25mm angle would need to be fixed to the concrete rather than the frame.

 

How would I attach the 25mm angle to the concrete block ? It would be adjacent to the edge of the concrete block so screws would be likely to break out. Is there some other adhesive that could be used and be stronger than the resin ?