Under vs. Over Screed Waterproofing: Considerations and Solutions 2023

This presentation recording is your essential guide to under and over screed waterproofing in Australia for 2023. Prepared by the Australian Institute of Waterproofing and delivered by David Previte.
Introduction 00:00
Regulations 01:20
Substrate 08:23
Protection 11:58
Tile Replacement 13:29
Junction Detailing 14:57
Overlay Bonding 21:02
Accountability 25:41
Mould & Bacteria 28:26
Creating Falls 32:00
Floor Heating 33:15
Program 34:57
Wall Sheet Warranty: 35:55
Case Studies 37:00
Under & Over Problems 47:23
No Waterproofing? 50:06
The Final Solution 52:35
IMPORTANT NOTE: due to time limitation i have not covered the compliance pathways for a waterproofing system that is applied both under and over the screed bed. As it is not specifically covered in AS3740:2021 and the issues that may arise, the dual system may require validation as a Performance Solution.
We start with an overview of Australian regulations, ensuring you understand the legal framework and compliance requirements for your waterproofing projects. Next, we delve into the heart of waterproofing methods, evaluating the strengths and weaknesses of both under and over screed options. Our detailed analysis offers insights into material selection, application techniques, and how to navigate the pros and cons of each method within the context of Australian standards.
Concluding with a forward-looking perspective, we explore the innovative approach of integrating both under and over screed waterproofing. This dual system presents a comprehensive solution but comes with its own set of challenges. We cover these pitfalls thoroughly, equipping you with the knowledge to implement effective waterproofing strategies that are both resilient and compliant.
Whether you're a seasoned builder, an architect, or a homeowner planning a project, this video provides invaluable insights into making informed decisions on waterproofing in Australia. Join the conversation and share your thoughts in the comments below.
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[@Woodbutcher00]

Great presentation very informative thank you for sharing.

[@DavidPrevite-WaterproofExpert]

thanks Gary, aiming to do more in the near future

[@LennyandVansWorld]

A great presentation. Just curious regarding considering AS3740.2021 clause 2.3.1 where installing a floor waste, the membrane is shall to be installed to a ‘substrate’ with a minimum fall (NCC overrides with 1:50max/1:80min). Under 3740.2021 substrate is defined as ‘surface to which the membrane is applied’. I may have missed any discussion on this in the presentation but generally speaking and in particular for 2 storey dwellings I would think this would require the membrane be installed on top of the screed (substrate) in many instances. Where a falls to floor wastes are required, waterproofing over the screed wouldn’t be doable under a lot of circumstances subject to AS3740.2021, so I would think Part 10.2 of the Housing Provisions would have to be the most practical choice if intending to waterproof under the screed. I.e AS3740.2021 wouldn’t be a chosen pathway commonly for this reason. Do you know if there are any other considerations to this when choosing which is best, under or over screed? Cheers

[@LennyandVansWorld]

A couple of typos above but the main point is waterproofing under a screed wouldn’t be able to be done subject to AS3740.2021 in a lot of circumstances where falls are required due to the clause and definition of substrate. Therefore surely the overwhelming majority are opting for the Housing Provisions pathway where a membrane doesn’t have to be installed to a substrate that’s has falls (under screed) but not sure if there is other considerations around this?

[@DavidPrevite-WaterproofExpert]

i believe housing provisions has its own pitfalls such as requiring a 25mm step down into the shower area which is also undesirable.

[@rio20d]

I think its always better if the licensed waterproofer is also licensed tiler so you wouldnt have this conflict of interest where the Tiler is riping up those membrane off just so he could get his tile installed the way he wanted it. We were lucky to have some renovation at our place and the tiler and the wateproofer is the same guy. Btw great presentation and very informative

[@DavidPrevite-WaterproofExpert]

Good point. Ive never seen a tiler willing damage their own work when they are providing the installation warranty for the work.

[@ramzi06may32]

An excellent presentation that answers many questions. Thanks David!