The checklist for waterproofing a property primarily focuses on a comprehensive design and pre-installation assessment to prevent costly defects and ensure the long-term integrity of the waterproofing system.
This proactive approach is crucial because waterproofing failures are among the most common and expensive issues in construction, often appearing months or even years after completion, necessitating extensive and disruptive repairs.
A thorough pre-waterproofing checklist, such as the C13A Waterproofing Design Checklist, acts as a structured guide to plan and document the waterproofing system before any work begins. It shifts the focus from a mere installation task to a detailed design process, ensuring that the right products are selected, surfaces are properly prepared, and all components of the waterproofing system are compatible.
1. General Considerations and Substrate Assessment
Before any membrane application, it's vital to assess the suitability and condition of the surfaces to be waterproofed.
Substrate Type and Suitability:
Verify that wall and floor substrates are appropriate for wet areas. For instance, fibre cement (FC) sheeting must be wet area-rated and of adequate thickness (e.g., at least 6mm for standard tiling). Water-resistant plasterboard can be used but with strict limitations on thickness, stud spacing, and mechanical fixings, and never where direct water exposure is likely. Direct fixing to masonry is generally discouraged as it can trap moisture. For floors, all timber must be waterproofed according to standards like AS3740:2021. Particleboard is typically only allowed internally and requires over-sheeting with FC.
Surface Conditions:
This is a critical step often overlooked.
Porous vs. non-porous:
Identify if the substrate is porous (e.g., concrete, FC sheeting) or non-porous (e.g., metals). This determines the type of primer required, as applying the wrong one can led to de-lamination.
Moisture Content:
Substrates must be sufficiently dry for the membrane to adhere and cure correctly. This requires using a moisture meter to test screeds and concrete, not just relying on visual inspection. Adhering to specified curing times (e.g., 28 days for concrete) is essential.
Contamination & Cleanliness:
The surface must be free from dust, oil, release agents, paint overspray, or other contaminants that could prevent proper bonding. Mechanical or chemical treatment may be necessary.
Condensation & Underside Moisture:
Check for signs of condensation or moisture originating from the underside of the substrate, especially in multi-storey buildings or tight spaces, as this can compromise the waterproofing.
Service Conditions & Movement: Consider the expected use of the area (e.g., heavy foot traffic, flexible vs. rigid substrates) and the potential for structural movement. This influences the required flexibility and durability of the membrane.
2. Membrane Selection
Choosing the correct waterproofing membrane is paramount, as not all products are suitable for every application.
Rigid or Flexible:
Select a membrane based on the substrate's movement characteristics. Flexible membranes are necessary for moving substrates like timber floors or suspended slabs, while rigid membranes suit stable surfaces.
Flexibility Class:
Membranes are classified (e.g., Class I, II, or III under AS4858) based on their elongation properties. Matching the membrane's flexibility class to the expected substrate movement is crucial to prevent cracking.
Abrasion and Root Resistance:
For trafficable areas like balconies, the membrane needs abrasion resistance. For planter boxes or green roofs, root resistance is a specific requirement.
Compatibility:
Ensure all components of the waterproofing system—primer, membrane, sealants, and adhesives for finishes—are compatible with each other and with the chosen substrate. Mixing products from different manufacturers without checking compatibility is a common cause of failure.
3. Curing Time and Conditions
Proper curing is as important as application, as it dictates the membrane's performance.
Wet Film Thickness (WFT) and Dry Film Thickness (DFT):
Every liquid membrane has a target thickness that must be achieved for optimal performance. Applying too thin will compromise effectiveness, while too thick can hinder proper curing. Using a wet film gauge during application is recommended.
Environmental Conditions:
Consider airflow, relative humidity, ambient temperature, and surface temperature. Most membranes have specific temperature and humidity ranges for proper application and curing. Ignoring these conditions can lead to bubbling, blistering, or de-bonding.
4. Installation Factors and Application Sequence
The practicalities of installation must be considered to ensure the system is applied correctly on-site.
Ease of Use:
Assess whether the product is a one-part or two-part system, its mixing requirements, and ease of application (e.g., spreading, rolling, spraying). Simpler systems are often applied more consistently.
Mixing Requirements:
For multi-part systems, precise mixing ratios, tools, and controlled batch sizes are essential. Improper mixing leads to improper curing.
Reinforcement and Bond Breakers:
Determine where reinforcement fabric is needed (e.g., wall-floor junctions) and the type and size of bond breakers required to accommodate movement. Failure to include these can lead to membrane cracking.
Screed Positioning and Application Sequence:
Decide whether the membrane will be installed above or below the screed, and ensure falls are correctly formed. Incorrect sequencing, such as waterproofing before waste locations are set, can necessitate expensive rework.
