STS foam board in shower area // tanking really necessary ?

[schakal]

Has anyone had first hand / long term experience with SBS foam boards for tiling ?

I am currently trying to tile a shower enclosure (3 walls)
Mainly due to uneven walls i have used 10mm STS tiling foam boards on all walls.
I am reading mixed views about priming and tanking these before tiling.

Firstly , I understand priming is to do with better adhesion of the tile to the board but aren`t these tiling boards meant to be tiles straight hence the price tag compared to plasterboard ,plywood etc?

Secondly , when you join 2 edges on the STS system you have to use the MEGA STRENGTH expanding foam type adhesive which goes hard like a glue while joining 2 edges together.
If water gets through the grout and behind the tile what could possibly happen ? go though the foam board layer into the foam and out the other end layer ?

Also if we are trying to stop water from getting through the grout , can i not just use a waterproof grout or seal the standard grout to stop water getting through ?

Apologies for million questions but i am trying not to overkill this thing and would like some real life experience /input on this.
People had shower cubicles for donkeys and they did survive without these massively overpriced tanking kits etc .

[aeromech3]

Surely this is not the same shower you asked Q about in April.
1st Manufacturers will sell their product to as wide a market as possible and in the case of STS system they only claim it will improve adhesion and they now have a primed board available!!! Truth is they don't suggest priming the back face of a tile and that is 50% of the adhesive area.
2nd Nothing much except if the correct adhesive is used except in freezing conditions.
3rd Water proof grout should be mandatory for any shower installation (sealing is only secondary as it is micron thick).
If you are lining a swimming pool you might go OTP and even then with expensive tap tap checks there are many new Tech pools which have tile failures (inside info).
In my early DIY experience I used marine ply which I primed with Bal, years later some tiles cracked and the blue colour of the BAL came through. I have used a backer board since, with a good water resistant flex adhesive and grout, no problems.
Wait for a Pro's answers but not if this is your only shower

[schakal]

Surely this is not the same shower you asked Q about in April.
1st Manufacturers will sell their product to as wide a market as possible and in the case of STS system they only claim it will improve adhesion and they now have a primed board available!!! Truth is they don't suggest priming the back face of a tile and that is 50% of the adhesive area.
2nd Nothing much except if the correct adhesive is used except in freezing conditions.
3rd Water proof grout should be mandatory for any shower installation (sealing is only secondary as it is micron thick).
If you are lining a swimming pool you might go OTP and even then with expensive tap tap checks there are many new Tech pools which have tile failures (inside info).
In my early DIY experience I used marine ply which I primed with Bal, years later some tiles cracked and the blue colour of the BAL came through. I have used a backer board since, with a good water resistant flex adhesive and grout, no problems.
Wait for a Pro's answers but not if this is your only shower

Thank you for the replies . Funny enough its the same shower area from April , yes I am dead slow :)

Good news is I finally got to the tiling stage , bad news is ,it appears , i have messed up the 90 degree between one of the short walls and the long one .
Its more like 93-94 degrees. In order to get the large tiles I have (30 x 75cm ) to sit at a 90 degree to the longer wall i need to back butter one end a lot.(20mm)
I can see on the tile adhesive instructions that i cant go over 10mm bedding though .

Can i however build up the STS foam board with a coat of adhesive (10mm) then tile over this tile adhesive after it is fully cured and dried ?
Would the dried /cured adhesive need to be primed before it can be tiled over ?

[aeromech3]

I would say no, I had to packer out one of my dry walls at home due original not square, removed the board to do it.

[Razor]

I agree with Aero. They only way to ensure longterm performance is to do it properly