OUTDOOR WORKING OUT
Lewis Lupton, UK head of training and technical support at ARDEX Group, discusses the main considerations when installing slabs or tiles outdoors.
Before the spring patio and terrace season gets into full swing, here we outline the two common methods of fixing – bound construction and traditional tiling.
BOUND CONSTRUCTION
We would recommend using the bound construction method when fixing onto pre-prepared Type 1 MOT sub-base – this involves the use of a bedding mortar mix and sometimes a priming slurry bonding coat.
Before fixing, you must ensure that ground conditions, and the subbase are suitable prior to the installation of a suitable Type 1 MOT grade, laid to the correct depth of 100mm (min) and fully compacted. It is crucial to ensure that the subbase should be stable and not liable to settlement.
It is important to note that when installed, all pavers and tiles should be free from standing or pooling water, so ensure that adequate falls are introduced to the Type 1 MOT or concrete to drain the water away to a suitable disposal point i.e. a gully, linear drain, soakaway or the edge of the terrace or patio. Direct surface water away from buildings where possible.
Where the patio is adjacent to the house, particular attention should be paid to drainage, and the patio’s height must be significantly below that of any damp proof courses, typically at least 150mm.
Once fully prepared, when using an ARDEX Group bedding mortar, we recommend that the Type 1 MOT or concrete subbase
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is primed with 2-3mm of an ARDEX Group priming slurry bond coat. However, in BS 7533, for site category IV i.e. patios, it is not essential to slurry the surface for all laying course materials or bedding mortar, but it will help in stabilising the MOT and increase the overall strength of the monolithic system.
˝Priming slurry acts as the ‘bond’ between the low-absorbent
porcelain tile and the mortar bed.˝
A bedding mortar should then be applied wet-on-wet and then compacted down to the required height, approximately 30mm.
When using an ARDEX Group bedding mortar, consider the use of a forced-action mixer, as traditional ‘free-fall’ or bell mixers aren’t suitable for this type of semi-dry screed mix and create clumping of the mixture.
The amount of mortar mixed and the area to be screeded should be limited so that trowelling off, finishing and tile fixing can be completed within the working time.
Where a new bay is laid against a set and hardened ARDEX Group mortar bed, it is recommended that such daywork joints are vertical and treated with an ARDEX Group priming slurry bond, with the bedding mortar applied onto the wet slurry.
www.tomorrowscontractfloors.co.uk
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