As per title says. Going to be tiling in a new shower cubicle. This area has had the walls re plastered, minus the skim coat. Is it essential to tank this area or can it be done without. Not fully aware of plaster's properties, can it be broken down by water damage?

Thanks in advance.

Best to tank it stops water entering the substrate and doing damage and yes plaster doesn't like water that's why its not used externally

hi mate,what background is it,if its browning or bonding best to skim 1st,no good to tile on.
if its just plasterboard or s/c as long as you seal it 1st they are ok

I would tank if the option is there..

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Gypsum undercoats need a finish before tiling..

What tiles are you fixing.

Tiles are 400mm x 300mm ceramic. The thinking was that the walls that were being tiled did not need the smooth skim finish and that the walls around the bath and sink would only be skimmed above tiled area where it is going to be painted.

As above. It is usually best to tank if you have to option but sounds like you will need to have a finishing coat as well.

Originally Posted by skeg

Tiles are 400mm x 300mm ceramic. The thinking was that the walls that were being tiled did not need the smooth skim finish and that the walls around the bath and sink would only be skimmed above tiled area where it is going to be painted.

As i said above,no point tanking if its bonding or browning,it will need skimming mate,plasterboard or s/c is fine as long as its primed/sealed


Whathay,i did it from me phone,the future is bright for me eh

What is the thinking behind it having to have the skimmed finish to be tiled on?

If plaster doesn't have a finishing coat, it does not have the strength to support the weight of tiling!

If asked by a client to tile a 'wet area' within a wetroom or bath / shower room on a plastered wall without tanking or protection, I would either refuse to do it or ask the client to sign an liability document.

We do an awful lot of wet rooms and shower rooms as complete projects and if the walls are cement / scratch coated / rendered or cleaned-off from old tiling, we either use a tanking cementous board, jointing tape and corner joints, or if the final wall thickness does not suit we use a roll of tankin sheet - various on the market including Butec / Nicobond / Lux etc. I wouldn't skim finish plaster and I'm not sure I agree about the weight theory either, if the plaster skim is really flat and smooth (not many are !) then all it means is that it makes the tiling an easier job.

Summary - always tank / seal / board all wet areas without fail - Its better to spend £100 on tanking than £1000 on ripping it all out 6 months down the line.

Do it right - Do it once !

Originally Posted by Richard Edwards

If asked by a client to tile a 'wet area' within a wetroom or bath / shower room on a plastered wall without tanking or protection, I would either refuse to do it or ask the client to sign an liability document.

We do an awful lot of wet rooms and shower rooms as complete projects and if the walls are cement / scratch coated / rendered or cleaned-off from old tiling, we either use a tanking cementous board, jointing tape and corner joints, or if the final wall thickness does not suit we use a roll of tankin sheet - various on the market including Butec / Nicobond / Lux etc. I wouldn't skim finish plaster and I'm not sure I agree about the weight theory either, if the plaster skim is really flat and smooth (not many are !) then all it means is that it makes the tiling an easier job.

Summary - always tank / seal / board all wet areas without fail - Its better to spend £100 on tanking than £1000 on ripping it all out 6 months down the line.

Do it right - Do it once !

You'd tile onto a bonding coat of plaster then?

Originally Posted by Richard Edwards

If asked by a client to tile a 'wet area' within a wetroom or bath / shower room on a plastered wall without tanking or protection, I would either refuse to do it or ask the client to sign an liability document.

We do an awful lot of wet rooms and shower rooms as complete projects and if the walls are cement / scratch coated / rendered or cleaned-off from old tiling, we either use a tanking cementous board, jointing tape and corner joints, or if the final wall thickness does not suit we use a roll of tankin sheet - various on the market including Butec / Nicobond / Lux etc. I wouldn't skim finish plaster and I'm not sure I agree about the weight theory either, if the plaster skim is really flat and smooth (not many are !) then all it means is that it makes the tiling an easier job.

Summary - always tank / seal / board all wet areas without fail - Its better to spend £100 on tanking than £1000 on ripping it all out 6 months down the line.

Do it right - Do it once !

as grumpy as said,would you tile onto browning or bonding,and if your plastering aint flat and smooth,he aint a plasterer

Originally Posted by grumpygrouter

You'd tile onto a bonding coat of plaster then?

Hi Grumpygrouter

Certainly not - If I had it in my power, and I do not, I would effectively ban Bonding Coat Plaster from all Bathroom installations - When I said Scratch Coat - I'm talking about cement render scratch coat -
Sorry if I did not make my self clear earlier in this post.

Here is an image to illustrate what I couldn't put over well

Oakley - McGrath Wet Room with Nat Stone Mosaics 011En-Comp.jpg

Originally Posted by Richard Edwards

Hi Grumpygrouter

Certainly not - If I had it in my power, and I do not, I would effectively ban Bonding Coat Plaster from all Bathroom installations - When I said Scratch Coat - I'm talking about cement render scratch coat -
Sorry if I did not make my self clear earlier in this post.

Here is an image to illustrate what I couldn't put over well

Oakley - McGrath Wet Room with Nat Stone Mosaics 011En-Comp.jpg

Cheers, thanks for clarifying.

hi, just a question, im a plumber by trade, but can also tile and plaster, i know your not supposed to tile over bonding, so will always skim over any bonding, and tank the walls, but what is the actual reason for this, ? someone wrote on here is that skim coat is stronger than the bonding, which is false, bonding dries like cement and is much harder than skim, i always thought it was because the bonding would take the moisture out adhesive and wouldnt dry properly, but that was just me having an educated guess, judging it to how skim reacts over the bonding, i have asked tilers and some know not to do it but cant explain why, and other tilers seem to think its fine to tile ober bonding

To answer your question RJM, The issue with Bonding Coat is that it sucks up moisture like a sponge and when it does, it starts to break down into a gritty mush and eventually becomes like a soggy playdoe. Not good anywhere in the home and especially in a bathroom or wet room. So in these rooms we would never use it or approve its use.

No the other side of the coin --

If you were using a 'proper tanking membrane' that was a genuine waterproof barrier and if you a 'bonding coat' within the structure of the wall surface, you might take a chance if you ' had ' to use it as longer as it could never come in contact with water or absorb water / water vapour from the surrounding air / materials etc.

That said, if you use a cementous board as part of the tanking barrier then you could mount this directly to either a scratch coat in a conventional build or directly to a stud wall in place of wall boards or plaster boards so both the bonding coat and the finish plaster finish becomes obsolete and this saves you time and money and eliminates the one major issue associated with BC.
There are other methods of tanking and each has it place in the tilers armoury.

The question of bonding coat, [BC] taking the moisture out of the adhesive is partically true, but to be honest if your still using dispersion adhesives in a bathroom [ie premixed tubbed] then you are in the minority and most pro tilers have switched completely to cement based powders and hence these are infinately more suitable for wet / high moisture areas.

Attached an image to demonstrate what I mean.

Hope this helps Oakley - McGrath Wet Room with Nat Stone Mosaics 011En-Comp.jpgThe grey board is a cementous tanking /construction board and the blue is a tanking sheet / cotton with PVC