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On Type 1 MOT sub-bases, ARDEX Group bedding mortars should be applied as required from minimum 25mm to maximum 100mm thicknesses, while on concrete substrates, it can be applied as required from min. 10mm to max. 100mm thicknesses.


To fix an external porcelain tile while the bedding mortar is still wet, apply another coat of priming slurry coat at 2-3mm on top of the bedding mortar, as well as a thin coat to the back of the tile or paver to ensure 100% coverage is achieved. This is also recommended with natural stone and slabs.


This step is critical, as the bedding mortar on its own will not naturally adhere to porcelain pavers. The priming slurry acts as the ‘bond’ between the low-absorbent porcelain tile and the mortar bed.


With fast setting pre-mixed mortars, grouting can commence in as little as 12 hours. With a hand-mixed sand/cement mortar mix this can be anything from 24-48 hours – significantly extending project timescales.


When using traditional OPC (Ordinary Portland Cement) and sand mixes, consideration must also be given the quality of sand along with its potential water content, as well as the prolonged set times associated with standard Portland cement formulas, which can be in excess of three weeks, even in good conditions.


We would recommend the use of a cementitious grout that is suitable for external use.


TRADITIONAL EXTERNAL TILING TO CONCRETE


When fixing porcelain or natural stone tiles (suitable for external use) we would recommend the direct fixing method – this is most suited when tiling direct to an existing concrete base.


This method is essentially the same as internal tiling and can be used for patios, terraces or driveways.


The caveat being that the concrete must cure for a minimum of six weeks, expansion joints may need to be incorporated, and falls will need to be included in the concrete to ensure rainwater drains away fully. An effective DPM should also be incorporated into any direct-to-earth subfloors – this is essential to protect the tiling solution from any subfloor moisture, which may cause joint discoloration and efflorescence


However, these installs also mean that 20mm (self-supporting tiles) are not a requirement. Porcelain of most thickness may be installed, as long as permitted for external use by the manufacturer. Which means potential reduced tile cost with easier handling and cutting and more tile choices available too.


Before direct fixing, the concrete base must be fully cured and free from efflorescence, laitance, dirt, polished finishes and other loose materials. These should be removed using suitable mechanical methods – some exposed aggregate should be visible in the surface but not loose.


No need for priming, simply dampen the surface with clean water (without pooling), prior to applying a smoothing compound or tile adhesive This will hugely improve the performance of your fixing solution.


Where necessary, you can smooth the surface with an external smoothing compound, however it is important then when doing


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so, falls created within the concrete pour for drainage, must be maintained. For isolated repairs, external repair mortars may also be considered.


Once the concrete is suitably prepared tiles can be fixed using a suitable external tile adhesive. Your selection may be based on weather considerations, and of course may also be impacted on the tile or stone type and size too.


˝Some external tile adhesives can be used directly onto tamped concrete without the


need to pre-smooth – but choose adhesives correctly, as not all can be ‘built up’.˝


Some external tile adhesives can be used directly onto tamped concrete without the need to pre-smooth – this may be an option if there are time or budget constraints, but choose your adhesives correctly, as not all can be ‘built up’.


Back-buttering of the tiles should always be considered – particularly on heavily keyed tiles to ensure 100% adhesive contact.


Solid-bed fixing of the tile is critical (as per British Standards) so that no voids remain beneath, and failure to do so can lead to costly failure, water entrapment, joint discoloration, efflorescence etc.


Once the adhesive has cured, grouting can commence with an appropriate cementitious grout which is approved for external use.


The ARDEX Group has a number of services to support installers including a nationwide team of Training and Technical Support Managers, plus trusted technical advisors available on the phone or on-line for our BAL, ARDEX and DUNLOP brands.


For full installation advice and on-site specifications, please call us on 01440 714939 or email us on info@ardex.co.uk.


www.ardex.com


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