NATURAL STONE SET IN When installed correctly, natural stone can achieve outstanding

Natural stone has a timeless beauty that comes in a wide range of colours, sizes and textures. It also has practical qualities to provide a durable surface that will look good for years to come, making it a favourable choice for commercial and domestic installations.

Installation of natural stone is a matter of knowledge and balance: the knowledge to identify the variables that can affect it – for example, adhesion to a suitable substrate – and the ability to get the right balance between the stone, the substrate, and the environmental conditions to which the stone will be subjected to on-site and in-service.

Granite, limestone, marble, travertine, sandstone, quartz, agglomerate and slate all have different physical properties and correct selection of a suitable tile adhesive is crucial, dependent upon where the stone is being installed.

The first consideration when tiling with natural stone is making sure your background is prepared correctly in accordance with the recommendations given in British Standards BS 5385 Part 5.

Substrate Preparation

New concrete floors must be air dried for at least six weeks before tiling, while new sand:cement screeds (unheated) require a minimum of three weeks.

Anhydrite or calcium sulfate screeds take approximately one day per mm up to 40mm to dry, and two days per mm for screeds greater than 40mm. It’s important that all

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laitance is removed after 2-6 days, while moisture levels should be less than 75% relative humidity (0.5% CM). This can take anywhere from 40 – 80 days, depending on thickness. Priming is also key before tiling commences on calcium sulfate screeds, as this creates an effective barrier between the gypsum and cement-based products – protecting against an adverse reaction e.g., ettringite.

There are fast-track solutions on the market including BAL Quickset Cement, or using the BAL Flexbone 2Easy uncoupling solution, which can be laid direct on new walkable screeds, or anhydrite at 1.5% CM.

If you’re tiling onto a screed that incorporates underfloor heating, there are more considerations before fixing can commence. This includes the proper commissioning of the heated screed before tiling.

For heated floor screeds, use of suitable uncoupling matting, such as BAL Rapid-Mat or BAL Flexbone, is recommended for installation of stone tiles.

For new walls, expect to fix over new Portland cement:sand render after at least two weeks’ drying – unless you’re using BAL Quickset Render or similar, which sets in two hours at 20°C.

No such waiting, though, if boards - such as new BAL Board - are the background substrate. With BAL Board, the weight limit is 100kg/m², making it perfect for use with natural stone tiles up to single storey.

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