How to seal yellow tongue for floor leveller compound on uneven floor?

[JohnA-007]

I will be laying ceramic tile underlay on top of leveller compound.

Any suggestion and advice will be greatly appreciated. Thank you.

PS: upstairs bathroom.

[JacobZ]

Hi @JohnA-007,

Welcome to the Bunnings Workshop community and thank you for your question.

I can't see a real need to seal the yellow tongue as you will require a waterproofing membrane be applied over the top as it is a wet area.

I would advise using Sika 20kg White Sikafloor 4020 FiberLevel Self Levelling and Smoothing Compound as it is a flexible self-levelling compound that can be applied over chipboard flooring. You would need to remove the wax coating from the yellow tongue before pouring using heavy grit sandpaper and either a floor sander or orbital sander depending on the size of the area. Once the waxy coating is removed, you will need to apply Sika 5L Sikafloor-08 Adhesive Primer as part of Sika's recommended application process. 

Once the floor leveller is applied, you will need to apply a waterproof membrane such as Crommelin 15L Shower Waterproofing Membrane over the top.

I would advise contacting a professional for the waterproofing as it is a licenced and regulated industry requiring a suitably trained person to undertake the waterproofing process.  

Please remember that at all stages of this process, specific personal protective equipment including, masks, eye protection, hearing protection, gloves, enclosed shoes, long sleeve shirts and long pants will be required.

If you need any further assistance or advice, please reach out.

Jacob

[JohnA-007]

Thanks Jacob for all the info.

My plan was to seal the existing yellow tongue with Bastion Waterbased Primer first, then use the Bastion Floor Leveller.

After that, I was going to lay 6mm Ceramic Tile Underlay.

I was then going to contact a company to membrane the whole bathroom and get it certified.

Does this sound OK?

Any info would be greatly appreciated. Thank you.

Regards,

John

[JacobZ]

Hi @JohnA-007,

My advice would be not to use the Bastion floor leveller.

The product datasheet for the Bastion floor leveller states that it is "designed for installation over new and existing concrete". It does not state that it is designed for use over timber or chipboard.

The reason I have advised you use SikaFloor 4020 is because it is a flexible levelling compound that allows for the slight expansion and contraction of the timber substrate.

The concern with using an inflexible leveller such as the Bastion one, is that it can cause cracking and instability beneath the waterproofing that can cause failure of the membrane over time.

I would advise you contact and speak with the waterproofer before installation of any levelling compounds as they will be able to give you advice on what they require for the waterproofing membrane to meet their warranty.

If you have any further questions, don't hesitate to ask.

Jacob

[JohnA-007]

Thanks Jacob, once again.

Previously, I mentioned that I'll be priming the yellow tongue first, then I will be using the levelling compound.

After that, I will be using 6mm Hardie Ceramic Tile Underlay.

The waterproofing membrane will be on top of this, not the levelling compound.

Does that mean I don't have to use the Hardie Ceramic Tile Underlay under the waterproof membrane ?

Thanks 

[JacobZ]

Hi @JohnA-007,

Thanks for your question, my apologies for being unclear.

You should still install the tile underlay over the levelling compound as the membrane needs a good solid surface for its application and there is no reference to self-levelling compound being a suitable substrate for waterproofing membrane. 

You will need to predrill all fixings to avoid cracking the levelling compound beneath. I'd advise not using the hammer function of any drill used for predrilling as this will increase the risk of cracking.

If you have any further questions, please get in touch.

Jacob

[JohnA-007]

Thank you, Jacob.

You've been a great help with my project.

Keep up the great work.

Cheers,

John

[JohnA-007]

Just an update, after more research, I'll be cutting out the existing yellow tongue up to the walls to the adjoining rooms.

Levelling the joists, and installing Secura flooring.

I think this is a much better solution rather than a bandaid solution.

More expensive, but longer lasting solution.

Thank you once again

Cheers,

John

[JacobZ]

Hi @JohnA-007,

Thank you for following up.

I'm glad to hear you are going to go with the Secura flooring as it will be a much better solution long term.

We love a bathroom reno on Workshop so please keep us updated as your project moves along, it would be great to see the end product.

If you need any more assistance as your project progresses, please don't hesitate to reach out.

Jacob

[JohnA-007]

Will post some photos when completed.

Thanks, Jacob.