Waterproofing compatibility – Membrane or you?
Waterproofing system incompatibility is often referred to where product chains are used outside of their intended parameters; however, the problem is far deeper. Who selects these materials? Who installs them? Who considers the follow-on links in the construction chain? Who is responsible when the system fails and, and who bares the cost for rectification? It may well be you, who falls into some or, all, of the scenarios above. Andrew Golle explains.
Waterproofing compatibility can be broken down into two core components:
- Product compatibility
- Trade compatibility
Both compatibility components must interact and be linked in a harmonious manner. What is the point of installing a premium grade membrane system, if following trades drill holes in it or cut lumps out to suite their installation processes?
Let’s explore both.
Waterproofing product compatibility
Membrane product compatibility comes down to whether the system is fi t for purpose, and whether all products are suitable for use as a complete and holistic system.
There is no individual waterproofing membrane that will suit all purposes. Individual site requirements require the selection of a system that will do the job intended. Consideration must be given to the intended use of the membrane, but also to compatibility with prior substrate preparation processes and, also following finishes. When selecting a waterproofing system we consider factors such as:
- Internal or external; curing times; compatibility with finishes; temperature ranges; root resistance; abrasive resistance; flexibility; cost; clean up etc.
Mismatching product components within the system can result in incompatibility. This should be viewed at the three installation stages of the membrane: substrate, membrane and finishes.
The substrate must be assessed to determine the appropriate processes involved to rectify or stabilise the substrate in preparation for membrane application. A damp substrate may require the installation of a negative pressure membrane prior to installing a topical membrane, not suitable for rising damp or hydrostatic pressure. A water based epoxy primer may be applied to a damp concrete substrate, prior to applying a solvent based polyurethane membrane. However this same hydro-epoxy may not be suitable as a primer to a dry substrate, where it will not bond sufficiently into dry concrete and introduces a rigid product under an otherwise class III flexible membrane (+300% extensibility).
The installation of solvent based polyurethane joint sealants beneath water based membranes can result in a breakdown in the membrane through solvent release. PU sealants are mistakenly used as a bond breaker, where a neutral cure silicone should be installed. Fast cure (FC) polyurethanes or Modified Silyl terminated sealants (MS) may be the appropriate sealant to use as a connector sealant with such membranes.
Another hot topic, throughout the eastern states, at the moment, revolves around who should provide falls in a wet area. Many believe that this responsibility falls onto the shoulders of the tiler, where AS 3740-2010 Waterproofing of Domestic Wet Areas and AS 4654.2-2012 Waterproofing Membranes for External Above Ground Use mandate minimum fall requirements for wet areas to manage surface drainage and reduce the effects of wind driven rain.
This is certainly true, to accommodate surface water. What about the membrane, where a membrane may be applied directly to the substrate beneath a screed? Most water based membranes are not suitable for full immersion, and if placed in such circumstances, may re-emulsify and certainly void the manufacturer’s installation warranties. AS 3740-2010 A3.5.1, states that, where a membrane is applied under the tile bed, a drainage system be provided within the tile bed, to drain the reservoir of moisture within the bed. This requirement refers to the rebating of the drainage control flanges to accept membrane drainage at the lowest level, and providing falls at membrane level. This can be achieved with proprietary levelling systems, prior to membrane application. This is the responsibility of the waterproofing applicator, as prescribed in the Certificate III Construction Waterproofing qualification critical aspects, CPCCWP 2004A Prepare Surfaces for Waterproofing Application.
Membrane installation compatibility is currently being compromised in the Sydney region, mainly on commercial sites. Solvent based polyurethane membranes are being installed beneath a tile screed to resist abrasion, immersion and reduce curing times. These membranes are not suitable or compatible with direct stick tiling, so a water based membrane is then applied to the wall areas for tiling compatibility. The problem lies with the overlap of both systems, at the base of the wall. Contact between a solvent based membrane and a water based membrane, ultimately result in degradation of the water based product where plasticiser migration occurs from the solvent product. This is catalysed by the presence of moisture and heat. The worst place in a shower to lap these dissimilar products is at the base of the shower wall, which has oodles of moisture and heat. Why would this practice be okay, where otherwise mixing a solvent based membrane with a water based tile adhesive would not?
Finishing processes need to be considered as part of the complete wet area system. Incompatibility with adhesives, ballasts and toppings often negates the effectiveness of the membrane. Bitumenous membranes are popular and appropriate products to use below ground. Many planter boxes fail where the membrane is terminated below soil levels for aesthetics, as one cannot dress renders or acrylic weather coats to these membranes, where exposed.
Moisture permeates the substrate behind these membranes causing bond failure and ultimately a functional breach. Waterproofing beneath vinyl is a requirement, where welded vinyls are classified as water resistant. The installation of solvent based vinyl glues onto water based membranes results in compatibility failure, where cement feather coats are not applied as an isolation layer.
Damage to waterproofing membranes by other trades is an industry reality. Other trades don’t seem to care, as it is not their problem. I can’t count how many times my membranes have been destroyed by plasterers intent on planting trestles on my membrane in order to set and sand the bathroom ceiling.
Ineffective supervision and a lack of communication are the main culprits, where construction times are pushed and we are therefore expected to work on top of each other and like it. This has to change, as it has become a general attitude throughout the industry. This adversely affects the waterproofing system from the very start of construction through to fit off.
Recently in North Queensland, a group of 88 houses mysteriously started having leaking showers. This was all blamed on the membrane used. Investigation revealed that the affliction was caused by substrate defects and negligent supervision. Recesses to shower slabs were over sized during the concrete pour with timber framing installed to overhang the recess. Wall sheeting was then installed, unsupported, where it projected into the recess. The waterproofing applicator failed to recognise the unsecured sheeting and continued to install membranes to flapping sheets. Tile screeds were placed and tiled. The tile screed thereby fractured the membrane where the unsupported sheeting deflected to the point of breaching the membrane.
This has become such a problem, that the developer is flood testing all showers on completion, removing plaster sheeting from the hallway, drilling through the framing bottom plate and finding water in the cavity beneath. Waterproofing and direct finish trades have always struggled with compatibility. Tiling contractors cutting tiles on membranes, mixing screed on membranes, and cutting out membrane protrusions is far too common an occurrence.
However poor communication between waterproofers and following trades is the major issue. Membrane application beneath tiling screeds is an accepted practice in some states. Abrasive damage to thin membrane films happens when the screed is not bonded to the membrane. The solution is to provide advice to the tiling contractor on how to provide a compatible bonded screed. The waterproofer should specify the required screed additive or bonding agent.
Drilling holes in the membrane just doesn’t make sense. Yet this is just what we do to our waterproofing systems when installing shower screens, rails, balustrades and cappings. The holes are neither reported nor sealed, and result in leaks that are often blamed on membrane failure.
What’s the solution?
Product compatibility all comes down to the correct specification and application of products within the range of their capabilities. Just doing what we did 20 years ago or “’cause Jono said so,” is not good enough. Proving the compatibility of materials and a system must be confirmed in writing.
Membrane manufacturers are only too willing to provide written specifications to ensure that their products are used correctly. Compiling a complete compatibility chain from a single supplier is the perfect solution. The second option is marrying up different manufacturers in writing. This should include all products including tile adhesives and penetration sealants.
Trade compatibility is a little harder to manage, but can be done. Builders are responsible to supervise all trades to ensure performance provisions are maintained. Seeking the above proof in writing must be the first step. Communicating compatibility can be managed by ensuring all information is documented on waterproofing application certificates, and this information made available to preparatory trades, finish trades and fit off crews.
Getting tilers and waterproofers to talk, agree on compatible materials, and co-operate by supporting each other’s processes will help avoid defects. The waterproofer should apply membrane detail as if they are going to lay the tiles themselves. Tilers should ensure mortar screeds are bonded and that complementary products are used.