Is it always necessary to tank up shower wall pre-tiling?

[Robin66]

Hi, I want to create a shower cubicle similar to the below. 2 walls of the cubicle will be tiled (porcelain or marble) and 2 will be glass panels. The shower tray will be 900*1600mm. I plan to install the shower tray onto the joists (1st floor suspended timber floor) into the corner and level the floor and then fix cement board to the walls and tile onto these and onto the shower tray. This means the cement board and the wall tiles will overhang the shower tray. I will also make the glass panels overhang the shower tray slightly and mastic round the edges.

While researching I thought I'd need to tank the shower cubicle on the floor and all the way up the walls. However, I spotted this review

https://www.screwfix.com/p/mapei-shower-waterproofing-kit/78484

"sorry but i just don’t get it. if you use the appropriate adhesives , grouts and sealants then theres absolutely no need for this lets be honest if water is getting behind your tiles , grout or sealant then it’s too late. no amount of ‘rubberised paint ‘ is going to save it. i’ve fitted dozens of shower cubicles over the years never used this before and never had a problem. "

Also I found a lot of people say it was only necessary to tank 12" up the wall ie. most of the wall near the shower would not be tanked. Since I'll have decent overhangs all around the tray I'm not sure I need to tank at all.

does anyone have experience of this?

 

[daggermark]

Water can get past grout, especially with a power shower, so I don't agree with the quoted comment.

Cement boards are water-resistant rather than waterproof, what is the existing wall made out of? Are you going to dot and dab the cement boards on?

 

[Robin66]

The walls are plastered brick, and yes, I was going to dot dab.

That comment along with some of the other reviews saying that the membrane had peeled of made me have doubts. But thinking about it some more, I could tile directly onto the plaster so if I apply the tanking kit first this will be cheaper and quicker than lining with cement boards.

It probably would be fine without still because it’ll be a spacious shower with low pressure flow and a fixed head so the walls will only have to deal with a bit of splash.

 

[daggermark]

In a big cubicle like that with low pressure I'd likely use cement boards and not bother with the tanking.

The important thing is that you design so that your tiles won't fail and so that the underlying wall isn't going to get drenched and be unable to dry out. From what you've said, this is unlikely. Tanking is obviously waterproof rather than resistant, but bear in mind that any tiny failures can allow moisture in behind which then can't escape.

 

[daggermark]

You may find this reading useful: https://ardex.co.uk/the-new-waterproofing-regulations-what-they-mean-to-you/

 

[Robin66]

Cool, thanks. You've confirmed my initial thoughts.

 

[23vc]

That reviewers comment in the first post is rubbish. Tiny bit of movement in the building structure can cause hairline cracks in grout, no matter how good the tiler was, and if it’s tanked it won’t leak. I always do it and have done for years, zero issues.
Arguably, you could ensure waterproofing with cement boards fitted correctly and totally sealed together and to the tray, but I’d just tank it every time.

 

[opps]

(porcelain or marble)

Porcelain will be maintenance free. Marble needs regular sealing.

If you don't do it frequently enough the surface will become rough to the touch and it may stain.