NATURAL STONE G WITH IT er advice on how to select the right fixing solution for natural stone.
Using an uncoupling mat is also recommended by The Stone Federation and BSI when fixing with natural stone.
The following extract is taken from The Stone Federation of Great Britain’s technical document Natural Stone – The Code of practice for Flooring Design and Installation of internal flooring (2015):
Clause 7.5 Uncoupling Membranes: “Uncoupling membrane systems provide an intermediate substrate between the stone covering and load bearing substrate e.g. timber and heated screeds.
“The membrane works by preventing stresses from the substrate being transferred into the stone covering; this prevents cracking and possibly delamination of the covering materials.”
British Standards 5385: Part 5: 2009 rev. 2011 Wall and Floor Tiling – Part 5 Design and installation of terrazzo, natural stone and agglomerated stone tile and slab flooring, code of practice states in paragraph B:
Clause 4.3 Time schedule “Where insufficient drying time and/or unsuitable drying conditions exist, the stone (and any adhesive) should be isolated from the screed below e.g. by using an uncoupling membrane. if at the design stage (see Clause 6) it becomes apparent that only shorter drying periods are available the stone should be set on an unbonded, reinforced semi-dry cement sand bed.”
A number of uncoupling mats are available on the market, including cavity mat systems, such as BAL Flexbone VAried; thin lightweight systems, such as BAL Rapid-Mat; and
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unbonded systems, like BAL Flexbone 2Easy. Each have their own unique properties for different situations – for example, heavy traffic, low height build-up, heritage work, etc.
When tiling with natural stone tiles, or any other tile, it is always important to incorporate movement joints in the floor. Current British Standards state that intermediate movement joints for interior floor tiling should be divided into maximum fields of 10 metres in each direction, whilst externally three metre intervals are required. Intermediate joints within the heated screed should not exceed panels of 40m².
For perimeter joints, a suitable neutral curing silicone or similar is generally advised in movement joints for stone tiling. That’s because acid curing sealants (e.g. acetoxy silicones) may chemically react with carbonates in the stone causing de-bonding at the edges with some types of natural stone, especially marble and limestone.
In high-traffic areas, however, sealant movement joints should be avoided altogether because they won’t prevent stone edge damage. In these cases, suitable proprietary pre-formed movement joints are recommended.
The risk of spoiling the effect of natural stone is greatest when installers reach the grouting stage. It’s generally wise to choose a grout colour that is similar to the stone tile colour – particularly with porous stone – and use a sealer to protect the stone from discolouration.
For full technical advice when installing natural stone and training that can be trusted, contact BAL Technical Advisory Service on 03330 030160.
www.bal-adhesives.com — 31 —
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