Tiling onto concrete - over old adhesive.....

[deepinthepow]

Hey folks. I did have an old username here....but couldn't find it for the life of me!

(Tiles are 190mmx570mm ceramic)

I'm finishing up my kitchen, and have a 3500mmx500mm section of wall to tile between the worktops and the wall units. This wall is cast concrete(not the usual no fines crap, but SOLID)

There is also a 1250mmx500mm section at the side(fresh plasterboard)

The concrete wall has been tiled previously, clearly dab and dot. No idea what adhesive they have used, but it is STUCK. I've tried various methods to remove it. Tiny chisel, Bolster, heat, water, steam, big hammer, blood, tears.....Its ON there!

Normally, I would have just fired up a sheet of 12mm plasterboard with some plasterboard adhesive(I like the foam....) or no nails etc, and then drilled/screwed it into the concrete at 600mm centres. Unfortunately I don't think I can afford the thickness, mainly as the the extractor fan has lights that are only a few mm from the wall.

So, I'm thinking I need to just tile over the old adhesive. Is this likely to prove a huge problem? At max its 3mm thick, and I was planning on using:
a 10mm square edge, with Mapegrip D2
PVA bond(Lol, Mapei G, ok for concrete and plasterboard?)


SO, solutions on a post card. I know its far from Ideal, but i'm hoping the surface of the tile might help any imperfections?



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[Flintstone]

Could you spare the depth to stick on a 6mm foam board such as marmox multiboard, using 10mm trowel ?

 

[deepinthepow]

I'll take another look. 10mm square notched adhesive = 5mm finished thickness? 6mm board, and around 3mm for the old grout - total roughly 14mm? I'll try moving the fan out by 14mm and see if it works.

Could I get away with a 6mm trowel if I use a board? that would take me to 11mm, which MIGHT work. The tiles JUST clear the light on their own. I can cut them slightly short and grout the gap at an angle