Starting From Brick, Plasterboard /adhesive Options

[Flintstone]

Your still relying on a seal between the tray and the membrane, a slight leak with that and your water is going down onto bare plasterboard

 

[SJPurdy]

However, I am reading conflicting information about whether the wall adhesive has to be flexible or not... I read a lot I discussions and no one seems to mention this.

Flex added to the description of a cement based adhesive generally means that it has more of the (expensive ) sticky component built into it. This means that a flex adhesive sticks more strongly to the tile and the substrate and can cope with more vibration/movement than a weaker bonding standard adhesive.
In your case as the PB will be fixed onto solid walls there should not be much movement/vibration in the walls that requires the higher strength adhesive to bond to the PB. However if larger format tiles are used or any size porcelain tiles then an adhesive with more sticking power will be required.
Some adhesive manufacturers have an adhesive strength option somewhere between their standard non modified and their single part flex. eg Weber set plus can be used to stick small medium sized porcelain, but to stick larger format porcelain or to stick to a timber substrate the Weber SPF would be more appropriate.
Some other manufacturers just add sufficient extra sticky component to make their standard adhesive suitable for porcelain (small-medium size) tiles.
As stated by others the modified adhesive can be cheaper than the unmodified because (eg) the shops sell more of it! Personally I would want the added strength (and peace of mind) of a modified adhesive (porcelain) even if only fitting ceramic tiles.

 

[olly330]

This is better
View attachment 81304

can i just double check that this adhesive is water resistant as it doesnt say on the product information.
Will be using it in bath and over bath shower area.

 

[White Room]

can i just double check that this adhesive is water resistant as it doesnt say on the product information.
Will be using it in bath and over bath shower area.

Yes it is water resistant.

 

[olly330]

Thanks for all the replies. Been working on other areas of the house but its good as its gives me time to plan out the bathroom properly and ensure everything is done correctly.

Im going to order tiles from tile magic as they are good on price and the adhesive prices seem good too.

Is the below pro flexible adhesive good enough for bathroom walls and floors, including shower area.
I have read the tech sheet, and they say in the description that is is suitable for walls and floors, flexible and water/frost resistant. Seems a good price at £11.51 per bag.

It will be ceramic tiles on walls and porcelain on the floor. Possibly white metro walls tiles which are small and grey medium sized floor tiles.

Also, is the grey colored one ok, I think that as ceramic/porcelain tiles are not porous it doesnt matter what colour of adhesive used?

Its difficult to wonder why the other mapei adhesives are more expensive when this one seems to tick all the boxes.... water resistant, flexible, suitable for both walls and floors....

Pro Flexible Porcelain & Stone Tile Adhesive (Grey) 20kg

 

[SJPurdy]

It will be ceramic tiles on walls and porcelain on the floor. Possibly white metro walls tiles which are small and grey medium sized floor tiles.

Also, is the grey colored one ok, I think that as ceramic/porcelain tiles are not porous it doesnt matter what colour of adhesive used?

If using white grout on the walls I would advise using a white adhesive also.