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How to apply bonded screed on waterproofing membrane?

Hi there,
I'm undergoing a full reno for my ensuite.
We are re-doing the floor, using Hardie secure for substrate and then screed and tiling.

We would like to do a double waterproofing system (i.e.: membrane under and over the screed). This, of course, while require a double flange system to ensure every layer is drained properly.

We would like to do a bonded screed (limitation on celing height). What combination of waperproofing membrane + primer + screed would you recommend to achieve this?

Thanks,

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EricL

Hello @MartinM

Please allow us to contact our suppliers regarding your query. As soon as we have more information, we'll get back to you as soon as possible.

Thank you for your patience.

Eric

EricL

Hello @MartinM

I had a look at the materials that the store carries, and I propose looking at the following products.

For the primer I suggest Davco 1L PrimeX Surface Primer. It is designed for compressed fibre cement sheeting, clean laitance free steel trowel concrete and float finish concrete.
For the membrane under the screed, I suggest the Davco 4L Grey K10 Plus Waterproofing Membrane. It is a premium performance, flexible, premixed, Class III, water based polyurethane waterproofing membrane designed for the use under tile, stone and other resilient finishes.
For the bonded screed, I recommend the Dunlop 1kg Express Wet Area Waterproofing. It is considered a bonding, liquid-applied, Class III membrane. It creates a flexible, fully adhered (bonded) waterproofing seal on surfaces like concrete, cement sheet, and plasterboard. Used with Dunlop Express Wet Area Tape, it forms a total system for waterproofing joints and corners.

In regard to the screed, I suggest looking at the Australian Builders 20kg Tile And Paver Screed. It is a good base for tiles, vinyl, floating floors, timber and carpet giving you a high-quality finish. This versatile product can also be applied as a bedding for outdoor pavers and to balconies & alfresco areas as an underlayment.

As to the double flange system, please speak to your tiler or plumber for a suitable system that is in-line with your current plumbing pipework under your floor.

If you have any other questions we can help with, please let us know.

Eric

MartinM

Thanks @EricL. Just a few question to ensure I understood correctly….

The primer will go betweent the FC sheet and the Davco Membrane. Does it also go on top of the screed and below the Dunlop membrane?
Would the Australian builders screed bond to this membrane without the need of a primer?

Thanks,

Martin

EricL

Hello @MartinM

Yes, Davco PrimeX and Davco K10 (Plus or Rapid) are fully compatible, and using them together on fiber cement (FC) sheet is the correct, recommended method for waterproofing. PrimeX is a specifically designed primer for reducing porosity on cement-based construction boards, such as compressed FC sheeting, ensuring a strong bond for the waterproofing membrane.

I'll have to get back you in regard to your second question. I need to find out if there is a specific primer to use on the Davco K10 if screeding is going on top of it.

Eric

EricL

Hello @MartinM

Just to be on the safe side, please don't purchase any of the products until I get back to you with more information.

Eric

MitchellMc

Hi @MartinM,

The installation instructions for Dunlop 1kg Express Wet Area Waterproofing state: Prime all areas to be waterproofed with DUNLOP PRIMER & ADDITIVE according to the instructions.

I'd recommend you read through this article from Ardex on Screeds and Waterproofing membranes. I haven't come across double-membraned systems before, so it's not something I am familiar with. Even with a standard single membrane over screed or screed over membrane system, we'd typically advise you to discuss specific product compatibilities and application with a licensed waterproofer, as they will be familiar with their application.

Bonded screeds are generally applied with a bonding slurry coat consisting of a liquid polymer additive mixed with cement. The bonding slurry is broomed thoroughly over the dry membrane, and the mixed wet screed mortar is applied over the still-wet bonding slurry. The liquid polymer additive is diluted with water and mixed into the screed mortar.

So, for a bonded screed, you'd need to add a product like Ardex WPM405 to the slurry and Australian Builder's screed. That's not something we keep in store, but our Special Orders team at your local store can look at getting some in for you.

Please let me know if you have any questions.

Mitchell

EricL

Hello @MartinM

Thank you for your patience. We have received the following response from Sika Technical:

Thanks for your inquiry and please ensure that the FC sheet floor has been installed according to the manufacturers recommendations and meets the current deflection standards.

Prime the FC sheeting with Davco Primex then when dry apply a slurry coat of Lanko 751 & GP cement mixed 1:1 followed by Sikafloor®-215 Rapid Screed engineered screed installed as Bonded Screed wet on wet to minimum 20mm thickness, according to the attached PDS.

Install the required falls in Sikafloor®-215 Rapid Screed to satisfy the relevant Australian Standards, when fully cured prime with Davco Primex and install Davco K10 Plus water-based, waterproofing membrane according to the current PDS, available online, and any relevant Australian Standards.

We don’t recommend applying membranes above and below the screed as this can trap moisture within the screed, potentially reducing strength and encouraging mold / bacteria growth and requires membrane layers to adhere to each other which may complicate application.

Please note that some of the products mentioned will need to be ordered at the special orders desk.

Please use the link below to obtain the current Product Data Sheet for any of these products to assist with application further.

Sika Product Data Sheets

For further technical inquiries they suggest calling the Sika Technical support team - +61 297575362.

If you need further assistance, please let us know.

Eric

MartinM

Thanks @MitchellMc @EricL for your valuable help!!

It looks the team from Sika didn't quite understood the double membrane concept. If a double puddle flange is installed, then there would not be moisture trap in the screed (see below a diagram, membrane in red, full link here). This is a method that I can't find it very popular, so I might just go with a simple membrane over the screed.

Ardex docs were very informative.

Thanks

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