How to lay porcelain slabs

The last few years has seen a massive increase in the popularity of external tiling installations using a range of materials, but primarily external self-supported porcelain (typically 20mm porcelain), slabs, pavers and natural stone. Want to find out how to lay porcelain slabs?

Here we outline the two most common installation methods using BAL’s new external tiling range.

Fixing onto pre-prepared Type 1 MOT sub-base or concrete where a build-up of more than 20mm is needed

This traditional wet-on-wet fixing method is favored most by landscapers and paving installers and involves the use of a semi-dry bedding mortar mix and a priming slurry bonding coat on the back of the tiles.

  1. Firstly ensure that the subbase is of a suitable Type 1 MOT grade, laid to the correct depth and fully compacted with a whacker plate.

The sub-base should be stable and not liable to settlement.

  1. All external pavers and tiles should be free of standing or pooling water, so ensure that adequate falls are introduced to the concrete or Type 1 MOT to drain the water towards a suitable disposal point i.e. a gully, linear drain or the edge of a terrace or patio. Wherever possible, surface water should be directed away from any buildings.
  2. 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.
  3. Once fully prepared, the Type 1 MOT or concrete subbase should be primed with 2-3mm of a slurry bonding coat such as BAL Priming Slurry Bond. Each bag of BAL Priming Slurry Bond should be mixed 6.4ltr of clean, cold water and then applied with a brush or roller.BAL Priming Slurry Bond poured onto Type 1 MOT
  4. A bedding mortar should then be applied wet-on-wet and then compacted down to the required height. One option is BAL Bedding Mortar, which should be mixed with 2 litres of water per 25kg bag to provide a semi-dry consistency. BAL Bedding Mortar should be mixed with a forced action mixer. Please note: Normal ‘free-‘fall’ mixers are not suitable for mixing semi-dry screed mortars. Use clean equipment and do not use other cement, lime or screed additives etc., in the mix.
  5. The working time of the mixed mortar is in excess of 1 hour at 20°C. 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.
  6. Where a new bay is laid against a set and hardened mortar bed, it is recommended that such daywork joints are vertical and treated with the BAL Priming Slurry Bond, with the BAL Bedding Mortar applied onto the wet slurry.
  7. On concrete substrates, BAL Bedding Mortar can be applied as required from min. 10mm to max. 100mm thicknesses.
  8. On Type 1 MOT sub-bases, BAL Bedding Mortar should be applied as required from min. 25mm to max. 100mm thicknesses.
  9. To fix an external porcelain tile, paver, slabs or natural stone, while the Bedding Mortar is still wet, apply another coat of BAL 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.
  10. Adjust the position of the porcelain tile, paver or slab and tap down with a rubber mallet.
  11. After 12 hours, the tiled surface can be grouted with BAL Terrace Grout. Hard wearing, water and frost-resistant, BAL Terrace Grout can be used for joint widths up to 15mm. Once applied, a first wash can be carried out after the grout has firmed up in the joint. A final wash-off can be carried out once the grout is fully set in the joints. BAL Terrace Grout can be subjected to normal site conditions after 24 hours.

BAL Terrace Grout applied to porcelain tile joints

Fixing external porcelain, pavers, slabs or natural stone onto new or damaged concrete suitable for direct tiling

This method uses BAL Level Out external leveller and is most suited when fixing porcelain, pavers, slabs or natural stone (suitable for external use) direct to an existing concrete base which may be rough or impact damaged. This direct fixing method is essentially the same as internal tiling and can be used for patios, terraces or driveways. The caveat being that expansion joints need to be incorporated into the subfloor, and falls will need to be added to ensure rainwater drains away fully. An effective DPM should also be incorporated into any direct-to-earth subfloors.

  1. Before direct fixing, the concrete base must be fully cured and free from efflorescence, laitance, dirt, polished concrete and other loose materials. These should be removed using suitable mechanical methods. Some exposed aggregate should be visible in the surface but not loose.
  2. Thoroughly dampen the substrate to be levelled with water, taking care not to leave any pools of water, before applying the product to the dampened substrate.
  3. Mix each bag required with approximately 5.25ltr of water. Please note that using excess water can reduce the strength of the set and hardened mortar. Each bag should be mixed thoroughly until a lump-free mortar is obtained. We would recommend using an electric mixing paddle with a 10m chuck at slow speed (600 -1000 rpm).
  4. If gradient levelling has is to be carried out, the water content can be reduced slightly.
  5. BAL Level Out should be applied within 30 minutes of mixing and can be applied from 2mm to 20mm in bed thickness.
  6. The mixed mortar will flow out and self-smooth during the first 10 minutes of its 30-minute working time. Spread the mortar using a steel trowel or float and then spike roll if required to remove any air pockets. A long handled smoothing trowel can be used to simplify the finishing operation.
  7. BAL Level Out can be tiled after approximately 3 hours. Once set, the freshly applied BAL Level Out should be protected from adverse climatic conditions, e.g. rapid drying air flow, direct strong sunlight, rain, frost etc., until hardened.
  8. Once BAL Level Out has fully cured, external tiles, porcelain, slabs, pavers or natural stone can be fixed using a suitable BAL tile adhesive such as BAL XL Floor One.
  9. XL Floor One should be mixed with 4.2ltr of water per 20kg and provides a pourable adhesive that can be built up to 25mm in bed depth. Fully wettable with a thixotropic nature, BAL XL Floor One One provides excellent coverage on the back of the tile – without the need of back buttering on flat surfaces. On heavily keyed tiles, back buttering may still be required.
  10. BAL XL Floor One should be applied using a large format trowel. It has a 1 hour pot life and sets in 6-8 hours for fast-track project completion.
  11. Once the adhesive is dry, grouting can commence with BAL Terrace Grout.

BAL 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 full installation advice and on-site specifications, please call BAL on 03330 030160 or email