UNDERFLOOR HEATING


separate areas of use or anything which penetrates the screed, such as columns or pillars. Movement joints are usually formed whilst the screed is being laid. It essential that movement control joints penetrate the full depth of the screed to the insulation layer.


Once tiling commences, movement joints should be incorporated to coincide with those in the screed. For floors subject to thermal changes, such as underfloor heating, floor areas should be divided up by movement joints into bays of size, no greater than 40m² for ceramic tiles and natural stone with an edge length of no greater than 8m i.e. square to rectangular panels with an 8 x 5 metre length to width ratio. For resin agglomerate tiles, the bay sizes should be reduced to 25m².


Movement joints should also be located at the junction between heated and unheated screed sections.


Further advice should be sought from BS 5385: Part 3: 2014, the code of practice for internal and external ceramic floor tiling and The Tile Association’s technical document Tiling to Heated Floors.


If using BAL Rapid-Mat or BAL Flexbone uncoupling mattings, they should be separated where intermediate movement joints are located.


Tile Adhesives


dependent upon the screed thickness and drying conditions on site.


Again, commissioning of the screed should be carried out in accordance with the heating manufacturer. The heating may also help with increasing the drying rate of the screed.


Undertile Electric Cable Heating systems


When using undertile electric heating cables, check with the manufacturer to ensure the system is compatible with the intended substrate and application areas, such as a kitchen or bathroom. An insulation/tile backing board may be required, dependent upon the substrate, and this should be compatible with the undertile floor heating system. The cables should be connected and checked for insulation and continuity (electrical) by a qualified electrician.


The cables, ideally, should be first encapsulated in a layer of a suitable smoothing and levelling compound such as BAL Level Max (recommended 5mm minimum). When using BAL Rapid Mat or BAL Flexbone uncoupling matting systems, the heating cables should be located below the uncoupling mattings.


Heating Mats


Again, check with the manufacturer that the chosen system is compatible with the floor substrate and to the environment in which it is being used and the recommended installation.


Movement Joints


Movement joints should be incorporated at all perimeters of the screed, including upstands, door thresholds between


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When tiling onto any underfloor heating system, the use of a suitable polymer modified adhesive is advised which is capable of withstanding thermal movements i.e. thermal gradients.


Suitable adhesives for use with heated screed floors and undertile floor heating include: BAL Single Part Flexible, BAL Supercover Rapid Flex, BAL Rapid Flex One, BAL Pourable One and BAL Max Flex Fibre and BAL Flex One.


BAL Pourable One is particularly designed for use with large-format floor tiles as it is pourable and can used up to 25mm bed depth for uncalibrated natural stone and levelling uneven floors (max 0.5m2


). Suitable Grout


As with your adhesive choice, your chosen grout should also be flexible to allow for thermal movement. Recommended BAL grouts include: BAL Micromax2, BAL Superflex Wide Joint Grout, BAL Easypoxy AG or BAL Floor Epoxy in wet room/hygienic areas.


Due to the large number of heating systems on the market, we would also recommend to contact BAL Technical and Advisory Service (TAS) for advice before any work is carried out.


At BAL, our Technical Advisory Service is fully equipped to provide support to contractors, architects and tilers – including NBS M40/M10/M20 specification assistance, on-site consultancy and expert technical advice.


Contact BAL Technical Advisory Service on 0845 600 1 222 or our Innovation and Technology Centre for training enquiries on 01782 591120.


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