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How to tile over shower tiles and replace toilet?

Hi there

I've been doing a lot of reading but struggling to get answers to a few questions.

1) I want to just directly tile over some very old shower tiles which I doubt have been waterproofed. Which primer and waterproofing product would be best to prepare the surface with? I have dunlop floor and wall tile adhesive.

2) I have the estillo arcylic shower screens. Is the best way to cut these to score them with a stanley knife and ruler and snap them?

3) I want to get a plumber to replace my side skew p trap toilet with a back to wall toilet and buld in like a box behind the toilet. Is that possible?

4) I have quite unlevel floors and am currently chipping the tiles of them. Next steps, I presume, are priming and then self levelling. Firstly I presume I can't skip some of the tile removal and just prime and level overtop of the remaining tiles? The tiles are 4mm thick and are stuck on well. I'm buying a chisel for my hammer drill but would love to just skip this step.

5) Secondly, what is the maximum height that I can self level? Does it depend on the brand? I was told it should only be a small amount but I'm reading it can be up to an inch?

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JacobZ

Hi @hannahmg,

Thank you for your questions about your bathroom and WC renovation.

For question 1, I'd suggest having a read through Can you waterproof when tiling over existing tiles where my colleague @MitchellMc has recommended a suitable method for waterproofing over existing tiles.

When you say you have the Estilo acrylic shower screen, are you referring to this Estilo 1900x900x2.2mm White Shower Wall? If so, then yes, scoring and snapping would be an effective method to cut them to size.

As for the toilet, replacing a side-skew pan with a back-to-wall toilet is definitely possible, but it is a plumber’s job and may involve altering the pipework through the floor or wall. Often, a small box or false wall is built to conceal the new connection, which ends up looking neat and modern once finished. I'd suggest discussing options with your plumber as it is important that you can still access the pipework for maintenance purposes.

Ideally, you should remove your tiles before priming and self-levelling, as primers and self-levellers struggle to bond to the glossy surface of tiles and removing them will ensure you get a good bond between the materials. It is a bit of work, but in the long run, it will be a much better method than leaving the existing tiles in place.

In terms of self-levelling depth, it varies from product to product, but they can often be used up to 25mm thick in a single pour. Before product selection, I would suggest having a good read through the relevant PDS (product data sheet) for your product, as it will explain the details around installation of that particular product, including what primers should be used and how thick it can be applied.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob

hannahmg

Hi there,

Firstly, this is an amazing community thanks for all your help so far!

I am about to start waterproofing tomorrow and would love some help with my Cromellin joins/sealer questions.

I have a tiled shower over bath, I am tiling over my existing tiles and following instructions previously provided here: Re: Can you waterproof when tiling over ... | Bunnings Workshop community

Beneath the tiles are even older tiles and concrete/brick walls. There is one small section that I have repaired with marine ply. See photos.

I am a bit apprehensive about getting all the joins right. My main point of confusion is about the bond breaking sealer. My understanding is it flexes slightly where there is movement but hold the two surfaces together so the waterproof membrane doesn't need to stretch as much? Do I use just it underneath the waterproof tape, or instead of?

I am about to start waterproofing my bathroom tomorrow with:

The Crommelin Tile on Tile Primer (TDS-Tile-on-Tile-Primer-November-2022.pdf)
- I will only use this on the tiles and overlap 1cm of the edge of the bath, but not the marine ply.
The Crommelin Hybrid Polyurethane Sealant (TDS-Hybrid-MS-Polyurethane-Sealant-June-2025.pdf)
- I will use this in marine ply/tile gap to fill it, on the edge of the tub/tiles, and the vertical junction of the two tiled walls. I think the only join that has any possibility to move is the marine ply/tile gap though. Is it needed in all these areas?
The Crommelin Waterproof tape (TDS-Waterproofing-Tape-November-2022.pdf)
- I will then apply this tape so it overlaps the tile/marine ply join (ontop of the sealant). I'm hoping then the two edges are held tight and reinforced with the tape. I will also apply this to the tile/tub edge and where the tiled walls meet.

The Crommelin Shower Proofing Membrane (TDS-Shower-Waterproofing-Membrane-November-2022.pdf)
- I will apply this ontop of everything else in a continuous layer.

Does the way I am planning to cover the joins sound ok?

Thanks in advance!

hannahmg

MitchellMc

Hi @hannahmg,

I’d like to start by clarifying that patched repairs to walls in wet areas, such as what you’ve done with the marine plywood, aren’t generally considered standard practice. In a shower-over-bath setup, the waterproofing system needs to form a continuous, unbroken barrier from the edge of the bath right up past the shower outlet. However, I do note that you do not believe there is currently a waterproofing layer under the existing tiles.

If you’re already tiling over two existing layers of tiles, the wall thickness will increase substantially. This can push your plumbing fittings too far back inside the wall, meaning your taps may no longer reach through to the plumbing work behind the tiles. In many cases, a plumber would need to extend the fittings forward to suit the new tile depth, which is worth confirming before you start. Another concern I have is whether the original tile adhesive has enough holding force to support three layers of tiles.

Given all this, my recommendation would be to remove the existing tiles (both layers), repair the wall properly with cement sheeting, waterproof it to code, and then retile. It’s a bigger job upfront, but it ensures the work is watertight, compliant, and long-lasting, unlike trying to patch and waterproof over a mixed surface, which is very difficult to make reliable.

If you do decide to go ahead with your current plan, what you've described would be the way to do it.

Please let me know if you have any questions.

Mitchell

hannahmg

Hi Mitchell,

Thanks for your advice!

A plumber has been to look at the taps and advised me to use a certain type so it could reach the edge.

The marine ply is a thin layer and behind the marine ply is a window frame. Will the window frame need to be cut away to put in the concrete sheeting? What trade would need to come in to put in the concrete sheeting?

Kind regards

MitchellMc

It would be cement Villaboard sheeting, which is what's used as a base for tiling in bathrooms @hannahmg. The type used on walls is typically around six millimetres thick, so hopefully, you won't need to cut into the window frame.

That said, the whole idea of patching small sections on a wall in a wet area isn’t standard practice. If there’s damage or a section that needs replacing, the correct approach is to remove all the tiles in that area, repair the wall behind it properly, and then start again with new sheeting and waterproofing. A handyperson would likely be able to replace the panel.

The method you described above is designed for sealing joints between continuous surfaces, such as wall-to-wall or wall-to-floor junctions, not for joining around a small repair panel. I’d be cautious about paying a trade to install a small piece of cement sheeting in that spot, as it will always remain a compromised section. The membrane might hold up for a while and act as a temporary solution, but it’s difficult to say how long it will last or whether it’s worth the expense to have trades come in for such a limited repair.

Let me tag @Nailbag to see if he has any thoughts.

Mitchell

hannahmg

Thanks for all your advice I really appreciate it. I really don't want to be worried about compromising the membrane and want peace of mind.

That's good to know that a handyperson would be able to replace the panel. I might try find someone to do it today or this weekend. Or would it be something relatively easy to do myself?

If I chip off all the tiles on that wall and get villaboard sheeting installed so that wall is uniform, do you think it would be ok to leave the other wall of tiles adjacent to it?

JacobZ

Hi @hannahmg,

Under the National Construction Code, specifically Part 10.2 Wet area waterproofing | NCC, direct wet areas, such as shower areas, require a waterproofing system, which includes a water-resistant base material. As that adjacent wall is inside this direct wet area, it would also need to use fibre cement sheeting to be compliant with modern waterproofing standards.

If you are going to the extent of removing the sheeting behind the taps, then it would certainly be worthwhile doing the adjacent wall too. It is also likely worth speaking with a licensed waterproofer for their assistance to ensure your shower area is waterproofed to the relevant modern standards to ensure your home is protected in the event of a leak.

Let me know if you have any further questions.

Jacob

Nailbag

Hi @hannahmg

As @MitchellMc mentioned, this type of patch job isn't standard practice and less than ideal in such an important part of your shower recess which is maintaining a waterproof barrier. Its all too common to hear about very expensive and disastrous flow on effects from waterproofing not done correctly. I was working on a home last week where it was recently renovated by qualified trades. But the waterproofing had failed due to a minor installation error. The entire bathroom was a redo and a rework of an adjoining bedroom wall.

So, in short, my advice is not to patch the wall but to replace it with cement sheeting, correctly waterproofed, tiled and then you have the option of any tap fittings.

Nailbag

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