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What self levelling compound suitable for putting on existing tiles?

I'm trying to figure out how to neatly close the gap between the base of a free standing tub and the porcelain tile and to prevent water from getting underneath and mould growing. The bath hasn't been installed as yet.

I don't like the idea of just putting silicone to fill in the gap. What I'm thinking of doing is:

- move the bath, put up temporary formwork to the dimensions of the bath base, prime the tiles and fill with self levelling compound.

- remove formwork and waterproof this area after it cures

- install bath and then finish the sides with white silicone or epoxy grout

Does this sound like the right plan of solving this isssue?

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MitchellMc

Welcome to the Bunnings Workshop community @newton. It's brilliant to have you join us, and many thanks for your question about installing a bath.

First, it’s worth asking why the freestanding bath isn’t sitting flush against the tiles. Is it because the tiles themselves aren’t level, or is there some protrusion or feet under the bath lifting it slightly? If the issue is something under the bath, creating a levelled area with self-levelling compound might not fully solve the problem. It could just raise the bath, increasing the gap. Baths carry a significant amount of weight when full, so the surface they sit on must be stable and level to avoid flexing or movement.

Self-levelling compounds do work well when there’s a substantial thickness, but if you’re trying to feather it out to a very thin layer under the bath, adhesion and long-term stability can be a concern, even if the tiles are primed. Because of that, it’s a good idea to check with the bath manufacturer for advice on what surface preparation or filling method they recommend. They may have specific guidance for installing their freestanding model safely.

Regarding your hesitation to just use silicone, that makes sense if the gap is quite large or if you’re concerned about durability. In that case, a flexible polyurethane sealant like Sika 11 FC could be a better option. It’s stronger and more durable than standard silicone and can handle slight movements without cracking or pulling away. You could still combine this with your levelling approach if needed: create a level base with self-levelling compound, waterproof it, install the bath, and then use polyurethane around the edges for a neat, long-lasting seal.

My main concern at the moment is that the bath may not be evenly supported around the exterior, which I would presume is a requirement for installation. I'd at least touch base with the manufacturer before proceeding with your plan.

Please let me know if you have any questions.

Mitchell

newton

Hi Mitchell, thanks for the response. The bath is right next to the shower and the floor is on an angle to allow for drainage of water, hence the gap.

The bath does have adjustable legs so if self levelling compound was used, it could be lowered to make it level. You raise a good point regarding the stability of the bath on a thin bed of compound. It would only be about 20mm thick at one edge and then taper off to the other edge.

Thanks for your suggestion of using the Sika product for more durability, I will certainly suggest that to the builder.

I will ask the question to Caroma and see if they have any recommendations on this. Thank you for your help!

newton

Hi Mitchell, I was contemplating an alternative solution and was thinking of using a 19mm x 19mm white PVC moulding to place around the base of the bath. Since the freestanding bath is essentially a rectangle, it would be easy to cut to length, and silicone it into place using Sika 11 FC. That way, the adjustable feet are directly in contact with the tiles as the base and the PVC moulding will greatly reduce any water entering from underneath especially with silicone in place. What are your thoughts?

MitchellMc

That sounds like a good idea. It should work well for that application @newton.

Mitchell

newton

Great thanks for your help 🙂

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