Number of screws in door lining

Hi,

I have got a door lining kit and was going to fix it to the wall opening with these fixings:

Link to B&Q

I thought I would use up all 16 fixings. 8 on each side. A pair of fixings in four places on one side. Now the problem is that I think the wall is too thin. It's 8.5cm and this includes 1cm of old plaster (rendering layer) on each side so there's only 6.5cm of real concrete.

Isn't the wall too thin to put two fixings on one level one next to each other?

What should I do? Shall I simply put fixings in one line vertically and maybe use fewer of them as well. Would 4 fixings on each side in vertical line would be sufficient?

I don't know, but i think i would be looking to use a maximum of 3 each side, provided they all take properly i don't think any more will be beneficial.

We use four or five fixings each side. Stagger them so that you have some each side.

If the lining needs more i.e. it's twisted or warped, then use more.