Best thing behind shower panels

Freddythefearlessfish

So I'm putting shower panels in the bathroom, but the wall behind isn't nice - ie it is uneven.  There are tiles on part of it and not on the other part, on one small section I tried to remove the tiles, but this makes things worse as it seems the tiles have not been tiled onto the smooth wall, rather the top half has been plastered potentially after the tiles fitted (so simply removing the tiles doesn't even the wall out).
The difference in thickness is approximately 7mm, so I was hoping to find something to pack the wall with (where there are no tiles) so that the shower panels go onto an almost vertical surface.

Options I've considered so far are:
plywood
cheap ceiling panels
tile backerboard (seems really expensive)
fibreboard
mdf
laminate floor insulation (the hard type)

Clearly none of these are really meant for this purpose.  I'm nervous of dampness distorting (despite the shower panels presumably stopping any actual liquid).

What say the experts?

Freddythefearlessfish

Also considered plasterboard - but I can't get any thin enough (ideally want about 6mm thickness)

Slinky

You want waterproof plasterboard behind a shower.

Nobbie1967

Fill and fix foam would attach them to the wall and makeup any unevenness. Probably considered a bodge, but saves faffing around.

danrv

I had a similar problem when doing my bathroom. I managed to get the tiles off, back to the bare Thermolite block wall. I then skimmed as best as I could, a coat of Zinsser Gardz then PVC shower panels (over bath).
Ideally get it back to the brickwork/wall but if tiles are stubborn, a couple of coats of plaster should get it all level. 
There's also HardieBacker board which can be skimmed over.

FreeBear

I wouldn't use MDF as it will swell should any moisture get to it. Plywood won't swell as much... Plasterboard, just no, same for most of the other materials on your list.

Instead, have a look at some of these products - https://www.screwfix.com/c/screws-nails-fixings/packers-shims/cat840018?page_size=100 (other suppliers available).

I'd either go for glazing packers, or these - https://www.screwfix.com/p/vitrex-laminate-wood-flooring-spacers-30-pack/181VJ

Soot2006

I just did the same and used gap filling grab adhesive. The panels themselves are fully waterproof so wasn't worried about what was behind them. I used a spirit level to hold them vertical for a few moments until they set in place. I don't consider it a bodge at all. I consider it the exact reason why these panels were invented - to save lazy, semi-competent DIYers like me a huge amount of time (and money). You'd never know and they are totally fixed. In fact, they'll probably outlive me.

Murmansk

If planning to install a shower onto those plastic panels I'd say make sure you have some wood behind the panel where you plan to install the shower riser as I have come across a number of cases where the riser has come off because the screws can't really get a decent grip going into the panel. 

danrv

I just drilled through my panels into the wall and put in rawl plugs for the riser and shower.
Not sure if the OP's using large Multipanel MDF type panels or PVC.
With either, agreed. Important to make sure it's solid material behind where the riser/shower goes. 

chris_n

Correx sheet? 6mm thick corrugated plastic sheet.

jimi_man

FreeBear said:

I wouldn't use MDF as it will swell should any moisture get to it. Plywood won't swell as much... Plasterboard, just no, same for most of the other materials on your list.

Instead, have a look at some of these products - https://www.screwfix.com/c/screws-nails-fixings/packers-shims/cat840018?page_size=100 (other suppliers available).

I'd either go for glazing packers, or these - https://www.screwfix.com/p/vitrex-laminate-wood-flooring-spacers-30-pack/181VJ

You won't need these for shower panels, the idea of them is that moisture doesn't get behind them. If it does then it doesn't really matter what you use, it's not going to do it any good. 

I had the same issue, tiles on one bit then plasterboard on another. Grab adhesive is perfect like the poster above suggested.