The Complexity Conundrum: Hobs, Setdowns, and Falls in Structural Concrete

I’ve recently come across a thought-provoking quote by Clyde Fitch: “Complexity creates a maze between you and success.” This quote resonates strongly with me when considering the intricate surface profiles of structural slabs compared to the simplicity of a flat slab. While there are undeniable benefits to a complex structural profile, it’s crucial to consider whether we are inadvertently increasing the list of potential issues that could lead to the failure of the waterproofing system.

The Benefits and Challenges of Structural Falls and Hobs

Incorporating hobs and structural falls ensures that wet areas can effectively contain and shed water to the drain, reducing the sole reliance on the waterproofing membrane for performance. However, achieving this level of precision requires a skill set that is often considered uncommon among concretors. The hectic nature of a concrete pour can further complicate the process, increasing the likelihood of errors and inconsistencies.

The Flat Slab Alternative: Building Falls in a Controlled Manner

An alternative approach worth considering is pouring a flat structural slab and subsequently building up the falls and upturns using carefully selected products in a more controlled manner. This method allows for greater precision and attention to detail, minimizing the potential for errors that could compromise the waterproofing system’s integrity.

By utilizing topping products after the structure is complete, professionals can create the necessary falls and upturns with greater control and accuracy. This approach not only simplifies the initial structural concrete pour but also allows for a more focused effort on ensuring the proper slopes and drainage patterns are achieved.

Weighing the Options: Simplicity vs. Complexity

As waterproofing design professionals, it is our responsibility to carefully evaluate the trade-offs between the benefits of a complex structural profile and the potential risks associated with its execution. While hobs and structural falls offer inherent advantages, the skill required to achieve them consistently and accurately may not always be readily available.

On the other hand, the flat slab alternative, coupled with a controlled build-up of falls and upturns, provides a more manageable and reliable approach to ensuring effective water management. By simplifying the initial structural concrete pour and focusing on the precise creation of falls and upturns afterward, we can reduce the potential for errors and increase the likelihood of a successful waterproofing system.

The Path to Success: Choosing the Right Approach

Ultimately, the decision between a complex structural profile and a flat structural slab with controlled fall build-up depends on various factors, including the project’s specific requirements, the skill level of the construction team, and the available resources. As professional consultants, our role is to assess these factors and recommend the approach that offers the best balance of effectiveness, reliability, and practicality.

By carefully considering the potential challenges and benefits of each approach, we can guide our clients towards a waterproofing solution that not only meets their needs but also minimizes the risk of failure. In the end, the path to success in waterproofing may lie in embracing simplicity and control, ensuring that the maze between us and a successful outcome is as straightforward as possible.

Written by: David Previte

www.linkedin.com/in/davidprevite

https://www.youtube.com/@DavidPrevite-WaterproofExpert

Liquid membranes are extensively utilised throughout Australia in a variety of contexts, including internal wet areas, balconies, subterranean applications, and even as UV-exposed rooftop membrane systems facing intense UV conditions, which demand robust and durable waterproofing solutions.

In the ever-changing landscape of liquid membrane technologies, it can be challenging to determine the most suitable system or technology for specific applications. This article aims to shed light on Wet Film Thickness (WFT) and Dry Film Thickness (DFT) concepts, paving the way for a deeper discussion on membrane applications in a subsequent article.

• WFT = Wet Film Thickness
• DFT = Dry Film Thickness

Every liquid membrane has a specific solids content (typically between 40-80%), in simple terms this means that the remaining percentage of the membrane will typically evaporate during the curing process.

As an example, if a membrane is applied at a rate of 800 micron (0.8mm) per coat and is 50% solids, once the membrane has cured you will be left with a coating that is 400 micron (0.4mm). This seems quite technical and you’re probably thinking to yourself “why do I need to know all this information, I’ll just slap it on nice and thick and it’ll be fine”- incorrect.

Many membranes I test for finished DFT (Dry Film Thickness) are well under the requirements and the applicators have stated they went real thick with the application.

Manufacturers should always specify the required DFT on their product’s technical data sheet. This specification is essential because each membrane must pass certain standards, such as AS4858 for internal wet area use or AS4654.1 for external above-ground use. The sample thickness used for these tests must be the minimum DFT applied in real-world scenarios.

It’s not uncommon in the market for manufacturers to test a product at a higher DFT (1.5-2mm) to achieve satisfactory results and on the technical data sheet state that it can be applied at lower DFT’s eg: 0.8=1.0mm. This is not deemed as a compliant application of the membrane.

Whatever sample thickness was used for the test results must be the minimum DFT the product can be applied at as there is no data/backing to confirm the membrane would work at a lower applied thickness.

The video below contains a brief demonstration of how to use a Wet Film Gauge.

Now that we’ve covered off on how critical it is to achieve the correct WFT/DFT for liquid membranes, lets cover off on the easiest ways to help achieve this on site:

1. Wet Film Thickness Indicators/combs: Using a wet film thickness comb is a great way to confirm that you’re applying the membrane at the correct thickness whilst it is wet, this approach also offers the advantage of allowing for adjustments; if the initial application is too thin, more membrane can be added promptly to prevent potential problems in the future.
2. Measuring the Application Area: A simple yet efficient strategy involves measuring the area where the membrane will be applied and calculating the product consumption per coat. For instance, if the technical data sheet of a membrane specifies coverage of 20m2 per 15L pail per coat, you can delineate areas of 20 square meters to ensure correct usage. Even with this method, it’s still advisable to verify the wet film thickness using a gauge to ensure accuracy and consistency in the application.
3. Ultrasonic Film Thickness testing: Once the membrane has been applied and is fully cured, ultrasonic film testing can be undertaken. This is specialised equipment that can provide the DFT of the membrane in a non-destructive manner. Ultrasonic testing is typically effective on various forms of membranes and is commonly performed by waterproofing inspectors, certifiers, and similar professionals to ensure compliance and quality.

I hope this information enhances your understanding of the significance of membrane thicknesses and provides insight into how to effectively implement testing methods for compliance in your upcoming waterproofing projects.

At this point in time, it is relatively common knowledge in our construction industry that a waterproofing system should be applied to a substrate with falls to drains in order to achieve suitable performance and lifespan of the system. This close connection between waterproofing, water-shedding and performance outcomes is appropriately explained in the TAFE NSW online course ‘Waterproofing Design Principles’ released this year. However, the question “but what is the minimum we can do and still achieve compliance with the NCC” is still voiced daily on construction sites when structural falls are identified to be insufficient.

This review is intended to address that question directly and in order to do so we have to start at the top of the NCC compliance hierarchy with ‘performance requirements’. Performance requirements typically define an outcome such as ‘water shall not enter the building’ and there are effectively two pathways for demonstrating that a design and/or construction has satisfied this requirement. The first being the use of a deemed-to-satisfy (DTS) solution and the second being the development of a performance solution. It is critical to note that where a design does not comply with DTS provisions adopted by the NCC, it will be considered a performance solution by default. This will be discussed further in the context of waterproofing external areas of a Class 2 residential project.

Typically considered the simplest option is a solution following DTS provisions, in this case that is AS4654.2:2012 is a standard provided by Standards Australia that has been adopted into the NCC. The provision for falls is covered with Part 2.5.2. Falls, that states a fall must exist to ensure water drains to the drainage outlet and the fall gradient should be 1:100. This wording of this provision is not overly detailed on the fall being located at the waterproofing level or the floor finish level and often leads to contention.

This wording of this provision is not overly detailed on the fall being located at the waterproofing level or the floor finish level and often leads to contention. Statements such “the standard does not say falls are needed at the waterproofing level so we will just put a fall in the floor finish screed” are often made to justify unsuitable construction works.

This reasoning is a fallacy that does not align with the NCC functional structure we established earlier and will result in non-compliant design/ construction.

This is due to the standards referenced by the NCC being deemed-to-satisfy provisions, meaning that if something is shown/stated in the standard it can be done and will be compliant. However if something is not clearly shown/stated then we must effectively fall back to consideration of performance and fit for purpose. So the next question is, is it possible to verify that a design without 1:100 falls at the membrane level provides sufficient performance to be considered a Performance Solution and compliant with the relevant NCC performance requirements? There are a few things to consider here.

The NCC provides the following requirement for performance solutions to be successful ‘the solution is at least equivalent to the Deemed-to-Satisfy Provisions’. Since AS4654.2:2012 states that there must be a fall in the substrate we can say that any performance solution must also include a fall to be considered suitable.

Many waterproofing materials currently available in the marketplace are not suitable for scenarios without falls that would result in ponded water. This is often clearly stated in the product data sheet to ensure the intended performance is achieved and where this is ignored will result in a voided product warranty and accelerated deterioration of the waterproofing system. A product that does not provide a warranty period for a specific scenario is typically not considered fit for purpose and would not be a valid performance solution.

Where fall does not exist to shed water to drains at the waterproofing level ponding will occur, often resulting in accelerated or other unwanted consequences such as efflorescence and debonding of finishes build-up.

In summary, where the need for fall at the membrane level is not clearly defined in the DTS provisions we must instead consider the design on a performance basis.

As there are numerous issues with a design that does not include water shedding it would often be difficult to justify that the design provides performance suitable to be considered a performance solution. Because of this we would say that most often a design without suitable falls at the membrane level is noncompliant with NCC performance requirements.

Any optimistic interpretation of requirements and provisions contrary to this is easily refuted will carry significant risk to the designer and builder.

David Previte – Managing Director

This article was originally published in the Australian Institute of Waterproofing Newsletter, Issue 21, January 2023

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The construction sector is provided an array of waterproofing systems for designers and/or installers to choose from in order to achieve project requirements. However, the choice can be limited if an individual lacks the pre-requisite knowledge on their strengths and limitations. Proper design and inspection of the waterproofing systems are therefore vital to ensure waterproofing quality, and it dictates the ultimate quality of waterproofing services. The quality of the services, therefore, depends on proper design criteria and artistry activities adhering to the standard guidelines. Under performing waterproofing is often costly for an asset owner; therefore, construction stakeholders must have should endeavour to implement quality improvement techniques to offset such a situation in the future. Methods for improving the quality of waterproofing vary depending on the stage of installation and the materials available to achieve the service. Here are 5 effective ways of improving waterproofing quality.

1. Design Documentation

These documents should be developed by professional with an in-depth knowledge of waterproofing products inherent strengths and limitations. The materials selection process should ensure that the best quality products are available with awareness on all environmental conditions known to the experts. Conformity to applicable standards is a requirement to quality since the design process is always aware of the diverse parameters. The documentation would also require a quality control regime to with the intention of ensuring conformity to the design. The documentation will incorporate inspection protocols that will ensure that the objectives stipulated in the document are met.

2. Installation

Installation works should be performed by licensed professional suitably trained with the specific materials stipulated in the design documentation. Field verification of the design is fundamental to confirm that the workmanship conforms to the initial design criterion. As a developer, you should ensure that part-time or approximate percentage inspection is adhered to for systematic monitoring of the ongoing works. The timing of the inspection should be such that it is before installation of topping, over burden, backfill or concrete pour as this will allow repair, replacement, or correction of components that are non-conforming or damaged. The firm in charge of quality control inspection should be reputable with significant knowledge in the field to ensure quality control inspections are undertaken effectively.

3. Warranty

Warranty is a guarantee that there will be a repair to the defective system once it becomes defective within a specified time. Waterproofing materials with warranty are most likely to conform to quality, as the manufacturer would not want to incur the extra costs related to maintenance. However, it is important to acknowledge that incorrect installation of a product will likely void the warranty being offered. A proactive waterproofing quality control program should focus on the common installation issues that lead to unwarranted waterproofing installations.

4. Pre-Construction Meeting

This meeting prior to waterproofing would focus on sequencing, techniques of construction, materials for waterproofing, and design criterion. It also assures warranty eligibility for the project as it entails the quality assurance plans. In the meeting, the representatives from the manufacturing firm focus on the guidelines for installation, criteria for reporting, relevant corrective actions for non-conformance, and the conditions acceptable for the substrate. In the same regard, there will be an opportunity for assessment and review of the sequencing and interface between trades, which improves clarity and increases the ultimate success of construction.

5. Reporting

The should contain information on all the aspects related to the activities, including all the deficiencies, which, according to the inspector, could potentially compromise the integrity of the waterproofing system. The report includes photos of the installation, inspection date and time, weather conditions, name of the inspector, and non-conformity actions. Action may include rework or repair so that the non-conforming section finds a lasting solution. The report illustrates the shortcomings and achievements of the installation process, which one can employ to inform future works or the best systems for waterproofing.

These techniques can work to improve the quality but are limited to the knowledge that one has in informing his or her choices. Choosing the best materials or inspection firm may be difficult if you do not have sufficient information on the market and trends that inform current materials. At Waterproofing Integrity, we recognise that every project is unique and we work together with our clients to develop a quality control regime targeting their specific needs.

Do you want to implement a waterproofing quality control regime? Call 1300 025 944 or complete our Contact Form to find out how today.