Getting mdf vertical

Does the back wall need to be vertical?

Why can't you fix the back wall mdf to the side wall mdf instead of to the wall itself?

Tony

Or fix the slope firstly by fitting straps adjusted to the vertical by packing them out then fixing the mdf to the straps .

Probably not, but Management may well decide otherwise once the job is 'finished'.

I could - I actually thought of building the 'box' outside the opening and then sliding it in - but am concerned about rigidity...

Not having an open fire in there then I take it? ;-)

I would use some 3x2" or possibly 2x2" for some vertical battens, which you could scribe and cut to the profile of the wall. Once you have fixed battens that are vertical on the facing side, the MDF will be easy.

Squirty foam at the back of the fireplace. Press the MDF gently onto the foam until it's vertical.

Owain

No, need to leave it clear for some old geezer on Sunday/Monday night...

But it does require a whole large can

Thanks for the suggestions.

I took the easier way out and built the box outside of the opening and then slid it in. It's already much more rigid than I expected (ooer!) but a couple of wedges and some architrave will hold it firmly in position.