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Can you apply floor leveller on old waterproof membrane?

Currently doing a bathroom reno. Just finished ripping up the old floor tiles in both the shower area and main bathroom area and found shower floor consisted of 16mm fibre cement sheeting, waterproof membrane, cement screed, thin tile set and then tiles. The main bathroom area consisted of yellow tongue flooring, waterproofing, thick screed, thin tile set and then tiles.

After ripping it up, the old water proof membrane is obviously torn, damaged and patchy due to my handy work.

Question1. Can I install floor leveller ontop of the old thin, damaged waterproof membrane in main bathroom area, then add tile underlay and then waterproof or do I need to remove ALL of the old membrane before the leveller.

Question2. What is the easiest way to remove old waterproof membrane if needed.

Thanx in advance.

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JacobZ

Hi @stevenab,

Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.

Unfortunately, it's not advisable to use a self-levelling compound over an old waterproofing membrane as it will struggle to bond to the surface beneath.

It would be much easier to attach the tile underlay first and then apply a self-levelling compound over the tile underlay. You can then waterproof over the self-levelling compound and tile over the top.

You can attach the tile underlay through the old fibre cement sheets into the floor joists by looking where the old screws are to determine the location of the joists. You can use Buildex 32mm Zinc Alloy 3 Star Head Fibre Cement Screws to fix the tile underlay in place.

Once the tile underlay is in place, I'd suggest using Lanko 173 Floor Leveller over the tile underlay to ensure you get a nice flat surface to waterproof and then tile over.

Let me know if you have any further questions, I'm more than happy to help.

Jacob

stevenab

Thanx for your reply Jacob. I have decided to remove the floor completely and replace it with James Hardie 22mm Scyon Secura sheets. As far as Im aware, the sheets need to be installed opposite direction to the floor joists, however, half of the bathroom the floor joists are running vertical and the other half of the bathroom floor has them running horizontal.

My question is, Am i ok to trim the sheets on the long side and join the long side and the short sides when the floor joist direction changes in the center of the bathroom ?

MitchellMc

Hi @stevenab,

The short answer is yes, you can do that. However, either way, whether you were to install new joists and continue running the sheets in the same direction or switch them to continue the perpendicular installation requirements, you're creating the need for a control joint there.

Unlike the tongue joints, the joint could experience flexing regardless of the supporting joist underneath. You'd need to have a control joint in your self-levelling and then one in your tiles. You need this joint to ensure the tiles and/or grouting above the joint doesn't crack.

Please let me know if you have any questions.

Mitchell

stevenab

Thanx Mitchell, so no control joint needed in the scyon sheets? I was thinking I could level the floor myself to eliminate the self levelling compound. Does this mean the only control joints then would be in the tiles ?

Screenshot_20240718_073528_Adobe Acrobat.jpg

MitchellMc

I'm sorry, @stevenab. Yes, a control joint is needed in the sheets. It's in Fig 10, where you'll use a 10mm backing rod. However, I'm now questioning how you'd use the backing rod for the sheet control joints with the self-levelling over it. Since this isn't specifically covered in the tech sheet, you might like to call the James Hardie Technical team directly on ph:131103 , so they can walk you through it.

Mitchell

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