Tiling expert ARDEX Australia has compiled a useful guide for installing modern large format porcelain tiles without worrying about adhesive performance.

The changes in surface texture and density of modern porcelain tiles are presenting challenges for tile installers, especially in the adhesive’s ability to bond these tiles to the substrates. While smaller porcelain tiles are simple to install, the newer large format style tiles with different mechanical properties in terms of hardness, density, porosity and surface texture, can create adhesion problems for low polymer thin set adhesives and poorly applied high polymer adhesives.

ARDEX noticed this problem in 2008 when large format porcelain tiles first began appearing in the market and ceramic tile adhesives used to fix them were displaying de-bonding. Produced by a fast firing process at higher temperatures to reduce energy consumption, improve production efficiency and minimise emissions, modern porcelain tiles display altered properties in comparison with older porcelain tiles. It was clear that the new closed, smooth and almost glasslike nature of the tile back was preventing some cement based tile adhesives from achieving sound bonding with the substrate.

Since medium polymer content adhesives do not have sufficient polymer content to produce the required chemical adhesion, ARDEX recommends that the higher polymer content of upper range C and R class adhesives be used for modern porcelain tiles.

ARDEX advises that the issues associated with installing large format porcelain tiles can be minimised by modifying the application methodologies and with better understanding and selection of tile adhesives.

Adhesive contact coverage

Obtaining sufficient adhesive contact coverage and spread to achieve a strong bond and an effective load carrying bed is a key challenge with large format tiles. When the adhesive contact coverage is reduced, so is the overall load capacity, but the actual strains exerted on the adhesive bed increase correspondingly. The same forces (dead load, wind, thermal and moisture related substrate drying movements) exist but applied over half to two thirds the contact area means the adhesive bed sees a higher level of applied stress where it is in contact with the substrate on one side and the tile on the other. ARDEX testing has found that when the contact coverage dropped to 80 per cent overall, the test load to failure dropped by around 30-40 per cent.

Adhesive’s open time

It is imperative that the tile is installed within the open time of the adhesive. When the open time is exceeded, the adhesive surface becomes dead to wetting and bonding, making tile application difficult. The installer is advised to only spread sufficient adhesive to lay a few tiles at a time; therefore, larger the size of the tile, the less overall area the adhesive should be spread.

Adhesive’s drying performance

Another consideration for laying large format porcelain tiles is the drying performance of the adhesive and development of strength. The non-porous barrier created by large porcelain tiles delays the loss of water from the adhesive as it cures. Whilst the adhesive might actually chemically cure, the matrix retains the unused water. In a smaller and porous tile, this water could be absorbed or diffused out through the tile joints. However, larger tiles have fewer and very narrow grout joints, reducing ability for drying quickly.

This retained moisture will not allow the adhesive to develop full strength with the actual strength being 30-50 per cent less than the equivalent dry or equilibrium strength. This delay needs to be taken into account where loadings are critical from an early age and is a good reason to use fast curing F rated adhesives.

ARDEX recommends flowable type cement based adhesives such as ARDEX X78 and systems with high polymer modification. High end single part or powder/liquid combination C2 rated adhesives with higher polymer levels will meet the adhesive coverage required on the back of a tile while providing superior overall bond, strength and resilience.

The polymer issue can also be addressed by applying a suitable ARDEX primer or bonding bridge to the back of the porcelain tile. Being polymeric liquids, the primers will effectively adhere to the back face of the tile and the adhesive.

ARDEX also suggests using a polymer rich adhesive slurry thin coat brush applied to the back of the tile, which is then placed wet on wet onto the notched adhesive bed.

As newer types of tiles are introduced in the market, tile installers have to simultaneously modify their installation process as well as products used to ensure a smooth, professional, strong and long-lasting finish. ARDEX draws on the expertise of a local and global Research & Development team that monitors tile manufacturing processes as well as emerging trends in the tile market. The Microtec reinforcement fibres found in ARDEX X77 and ARDEX X78 tile adhesives are an example of ARDEX’s constantly evolving technology innovations.

A technical paper on installing modern large format porcelain tiles can be downloaded from the ARDEX website.