Tiling and Waterproofing are Often Installed Together and are Common Building Defects found During Sydney Property Inspections
External tiling and waterproofing are typically found together in residential buildings. Commonly installed on the external floors of elevated balconies or terrace areas, they play a vital role in maintaining the ‘watertight’ building envelope and providing adequate surface drainage.
Unsurprisingly, waterproof membrane defects are the most common building defect our inspectors find. This includes wet areas such as bathrooms and laundries as well as elevated external balconies that are located above internal areas.
For the purpose of this discussion we will be talking about external waterproofing and the tiling that is normally installed on top.
Unfortunately waterproofing defects are all too common. Waterproofing defects mainly arise from a lack of construction detailing in the design stage and a lack of construction oversight, as well as poor workmanship and cost cutting on behalf of trades.
It is important to understand tiling and screeds below (sand cement layer) are not waterproof and can hold water, permently in some circumstances.
External Waterproofing is Determined By Australian Standard AS4654.1 “Waterproofing Membranes for Above Ground External Use”.
AS4654.1 outlines the requirements for external above ground waterproofing, however, reference to AS4654.2 is also required for “Design and Installation” of external waterproof membranes.
As stated in the Forward “Industry research and experience has shown that the design of roofs, decks, balconies and planter boxes contributes to many of the failures of waterproofing mediums used and by setting a standard for materials design and installation for construction, the failure rate will be dramatically reduced”.
The exact method of installation will depend on the type of waterproofing system installed. The Standard outlines the following waterproofing systems for external above ground use.
a) Ballasted Membranes – The membrane is held down by ‘ballast’ such as stones or gravel.
b) Bonded Membranes – As the name implies, the membrane material is fully bonded to the substrate, such as liquid membranes.
c) Inverted Roof Membrane Assembly (IRMA) – A system where a ballasted roof insulation is placed on top of a membrane.
d) Mechanically fixed membranes – Membrane held down by mechanical fasteners.
e) Partially Bonded Membranes – A system where only part of the surface area of the membrane is designed to be bonded to the substrate.
Generally speaking fully bonded and ballasted membranes tend to be the most common in restidential buildings.
The ‘General Principals’ of External Waterproofing
External membranes need to be more durable and abe to handle large dimensional changes. External membranes are exposed to more extreme thermal differences as well as exposure to the elements and continuous immersion.
The waterproof membrane should be designed as a ‘drained tank’ similar to a shower cubicle or shower tray, where the membrane turns up walls and over tops of walls etc.
The membrane product should be suitable for continuous immersion.
The design stage is crucial in the fight against membrane failure. The building designers should detail waterproofing systems for all relevant parts of the building and these drawings must be communicated with the builder and relevant trades. For example external floor transitions are particularly problematic, such as a balcony door. It is essential to understand the transition includes ‘freeboard’ between internal and external floor levels. A minimum step-down of 100mm is recommended to prevent standing water penetration between external and internal areas. A ‘level transition’ should only be attempted where the pavers are suspended with drainage installed below or adjacent to door and window sills. The surface area of the windows and doors and the direction of exposure (ie south east) can also contribute significantly to the volume of water from storm conditions.
The door and window sills must have a way to ‘shed’ this excess water. Small drainage holes are a common cause of leaks with large exposed areas of glass.
Membranes should be protected from damage by subsequent trades (tilers) as repairs to minor damage down the track are usually not possible, requiring a complete ‘do-over’. Some membranes can be repaired, provided the leak location is traced.
‘Bond breakers’ are required at material changes and uptstand corners to allow for thermal movement.
Membrane application certification should form part of the building certification system and the final documents – the Occupation Certificate and the Waterproofing certificates should be obtained prior to settlement.
External Tiling
External tiling must be installed with suitable falls to drainage (no ponding water) and avoid negatively impacting the waterproof membrane below. The exact method of tile installation will depend on the waterproof membrane system used.
Ceramic and stone tiles absorb heaps of thermal energy where exposed to direct sunlight. This creates heat which causes thermal expansion in the tile, dimensionally. This thermal movement is a common cause of membrane failure and tile deterioration, especially on larger balconies and terraces.
A slip sheet between the membrane and the tiling is recommended to prevent damage to the membrane through thermal movement. The slip sheet requirements will differ depending on the amount of thermal energy the area receives. Tiles can ‘soak up heat’ causing significant dimensional changes over the distance of a regular outdoor area.
A gap is required around the perimeter – between the edge tile and the wall material. This is filled with suitable flexible sealant to act as an expansion joint around the perimeter.
Expansion joints in the tiling are recommended where an area is greater than 16m2. This also depends on the thermal exposure of the floor tiling. More regular joints are recommended in extreme thermal locations.
In these more thermally extreme situations, reinforcement of the tiling screed is recommened, however galvanised wire products are not suitable due to potential corrosion.
Waterproofing additives (such as Silasec) should be used with screeds to reduce the risk of efflorescense and mineral staining caused by leaching of the tile substrates. A simple additive can reduce or eliminate this common defect 5-10 years down the track.
External floor tiles should be installed with a gradient to drainage. A minimum of 1:60, but preferably more. Surface water should not be ponding on the floor tiles.
External trafficable tiles should also comply with ‘slip ratings’ suitable for the installation location, such as around swimming pools or on exposed stairs etc. Higher Slip ratings generally correspond with a more textured tile surface, which in turn leads to faster ‘soiling and staining’ and greater need for cleaning.
