Best way to hang heavy shelf on insulated plaster board

[Redwren]

Hi, super newbie here. I have some heavy floating shelves to hang on a wall which is essentially insulated plasterboard, a cavity and then standard brick.

The shelves come with fittings for a solid wall which is no good.

If I fit the solid wall bracket to the masonry (through the plasterboard) by reducing the length of the rod in the shelf, will this be a reasonable work around?

Or am I cutting too many corners with this approach? Any advice will be appreciated!

 

[He who knows]

How much redecorating effort do you fancy?

 

[Redwren]

How much redecorating effort do you fancy?

Lol!!

Is it likely to be the weight of the shelf that is the reason for needing a solid wall; or the bracket is suitable only for a solid wall?

The shelf is a single piece of wood, nothing spectacular. I kind of want the answer to be the latter

 

[captainb]

Why can’t you fix it into the studs ?

 

[piglet11]

You have an engineering problem here.
Plasterboard is quite good at taking sheer forces i.e. forces in the same plane as the board, but it's not good with forces that are horizontal to the plane.
Heavy shelves will do both.
I assume by uninsulated board, you mean standard board 12-mm with a layer of foam insulation on the back.
You can get a good fixing by using fixings called Intersets by Rawlplug.
They are designed for board with no insulation, but possibly, you could get them to hold by fixing using a longer screw to set them.
Once set, you can use a threaded stud of any length.
As captinb says, your best bet is to find the studs.
If the boards have been nailed, use a powerful magnet to find the nail heads and draw a line down the stud.
Personally, I would hoik out the nails - use a catspaw nail puller - and get some screws in to fix the board. If you don't, the shelves will pull the board off.
I would do that whether you use the studs or not.
If the board has been stuck to the studs, explore with a narrow screwdriver to find the studs, then screw - board that has been stuck may not take the weight of shelves.
If the shelves are really heavy, you might have to cut some holes in the board and get a threaded stud into the brickwork using a chemical (resin) fix I've done that for wall hung lavvies on plasterboard. It gives you the opportunity to get some timber behind the plasterboard.