Shower tanking advice (yes another thread) - but a slight twist?

[Herbie]

Hi everyone,

Just looking for some advice? I am a reasonably newbie tiler but reasonably competent and have decided what I really need in my life is a shower over my bath (was just a bath previously).
There was a row of three tiles above the tub and then just painted wall so the solution appeared to me to be to tile to the ceiling, fit a screen and employ my friendly plumber to work his magic.
However - having taken the old tiles off, where I thought I would see left over adhesive and plaster is a band of unfinished plaster where presumably the bath fitted lower than the plasterer thought it would and slapped in and 'no one would ever know' as the tiles were going there....
So, where I thought I would (rightly or wrongly) dodge tanking as the tiles would be going onto a sealed wall, I am faced with a band of super porous bare plaster above the bath which is far from ideal.
Sooooooooooooo. How best to go about this? As I live in a flat I dont really want to be paying for downstairs bathroom to be decorated when it all goes wrong - and I quite appreciate that there maybe additional costs - but I would want to do it properly and get it right first time.
Thanks!

 

[Herbie]

View attachment 51685 View attachment 51686


Pics!

 

[JJS1410]

Not fully sure what you mean by a sealed wall? Without tanking any substrate would end up soaking up the moisture (assuming enough water ends up on the tiles), its how the substrate handles it that differentiates them.
So I personally tank the substrate to ensure longevity of the job, and to minimise/eradicate the impact of the water penetrating the tiles and grout.
In your pics it is not clear what is between the bath and plaster, is it just a patch plaster? If you think this surface is not smooth enough or isn't keyed into the plaster above then I'd remove it and re plaster it then tank.

 

[Herbie]

Not fully sure what you mean by a sealed wall? Without tanking any substrate would end up soaking up the moisture (assuming enough water ends up on the tiles), its how the substrate handles it that differentiates them.
So I personally tank the substrate to ensure longevity of the job, and to minimise/eradicate the impact of the water penetrating the tiles and grout.
In your pics it is not clear what is between the bath and plaster, is it just a patch plaster? If you think this surface is not smooth enough or isn't keyed into the plaster above then I'd remove it and re plaster it then tank.

Hiya, thanks for the reply - having got back in and had a look (the old tiles were taken off in a bit of a rush) it would seem that the 'band' is pure sand and cement and it also explains why it hasnt 'taken' to the plaster above. So I have a 2 inch strip of S/C and then plaster, ugh. Not ideal. It also explains the tile remnants on the S/C as obviously it provides an excellent key and the tile adhesive removal leaves it even more looking like a lunar crater
What a pain - do I seal the mess that has been revealed using a propitiatory sealant or chip it out and properly plaster and THEN seal?
What a pain - but it isn't one I intend to inflict on anyone else - if there is a 'right' answer I want to make good not only for my own peace of mind but also I'd hate to pass on an issue I could fix

 

[AliGage]

Hi and welcome Herbie.

I see this sort of thing on old DSS properties all the time. It looks like bonding plaster to me. At some point the bath has been replaced and because (at least the two on show) all three walls are brick rather than stud plaster and render etc has had to be removed to get the old bath out and a new bath in.

How sound is the "bonding". If you give the area a tap with your knuckles does any of it sound hollow? If it's sound what i would do is this.

Scrap of the remnents of adhesive and get all lumps and bumps off from the old tiles. Give all that paint a sand back to reveal the finishing coat of plaster.
Prime the whole area with SBR mixed 1:1 with water. might need a couple of coats.
Mix up some SPF adhesive and using the back of a trowel (flat side) skim over the bonding coat pressing adhesive into and cracks between the bonding and skim coat etc.
Tank the area with a waterproof membrane fixed with a SPF adhesive.
Then you should be all set to tile once the adhesive has set/gone off.

 

[Herbie]

Thanks for the reply Al,

The explanation for the plaster oddity does fit and yeah, the third wall is the same - theres no difference there. I wish when they had swapped the bath out they'd have put the bath the other way round! no matter - I am certainly not going through the aggro of doing it!
The sanding of the wall is going to be somewhat laborious but so be it. Raiding my tool cupboard it would seem I have any amount of sandpaper and one of those flat sheet sander thingys - so it will be that unless there is a better tool? I am perfectly happy to use this as an excuse to buy a belt sander if this will make all the difference?
The infil plaster is thankfully pretty sound so I can work with it rather than beginning afresh.
Everything else written makes sense - and seems logical though where you say 'a waterproof membrane fixed with SPF' this left me thinking a bit. Do you mean a physical membrane - like a mat or something like Mapei Aqua Defence? I can appreciate the simplicity of the liquid membrane option if so!
Oh - one last thing - hope you don't mind - where you make mention of SPF adhesive I had kinda planned on using BAL White Star. I fully understand the pros and cons between each but considered, as an occasional tiler, that the premix would suit me better. Would you strongly advise against this or can I substitute the White Star for the SPF for the cracks between the plasters?
Thanks again for the above reply - I was talking to a friend yesterday who declared he would paint the whole area with a couple of coats of watered down PVA and that would be that. I'd like to be a little more sophisticated than that!

 

[AliGage]

Hi Herbie,

A belt sander would make one hell of a mess! What tiles are you planning on fixing? As far as size etc.
You can test the painted area with some ducktape. Place a piece across, leave for around 20-30 then remove. If paint comes with it then the paint certainly needs to come off.
Although whitestar is in my opinion, and im sure many others the best tubbed adhesive on the market. It certainly is the most popular. Cement based adhesive is definately the way to go. I wouldn't advise filling cracks with tubbed gear as it tends to crack when applied too thick/deep when it's drying out.
A bag of single part flexible would not only be cheaper to purchase, but will do a far better job. (BAL's purple bag). Don't be talked into rapid setting, take your time and mix it right, what's a day in the grand scheme of things.
I use the liquid membranes/waterproof coatings as my prefered choice. But because you're bridging two different substrate materials, even if it is such a small area i would suggest a matting instead. As i say, after priming the area with a suitable primer (NOT PVA) fill the cracks, apply a your adhesive and fixing matting as per the instructions. Skim over any joins of the matting with adhesive and allow to dry.

You should then be good to tile, good luck!

 

[Herbie]

OK! Well, no belt sander but my hand sander also made a hell of a mess and apparently I promised my wife (twice) yesterday that I would take all the stuff out of the bathroom before I started - ah well - you can't have everything!
But anyway - the walls are now, if not 100% smooth, much better and we are ready for the next stage.
The tiles I have bought are fairly generic 25x20 tiles and the paint above is in good order so I have left it alone. I think I have a reasonable handle on how to proceed though what do I do about where the wall meets the bath? Currently there is a small, rough gap all the way round (2mm). Should I be running the membrane slightly onto the bath itself to create a seal beneath the bottom tile? Or stop it where the bath meets the wall? Though I have just thought of a question - if everything is waterproofed and some grout DOES eventually fail and water gets in - where does it go? with everything sealed it wont ever be able to get out? ah - just realised - that's probably the point!
I will be popping to Topps tiles tomorrow to do some shopping unless there is anywhere else I should be going? Oddly screwfix doesnt seem to carry the waterproofing membrane - but I will be buying the BAL SPF as opposed to the white star.....
Thanks for all the tips!