How to Install Natural Stone Flooring over Underfloor Heating. Preparation, Installation and Applying Adhesive (1)
If you consider installing natural stone flooring over underfloor heating you should know the benefits: slips-resistance (reduced risk of accidents due to slipping) and an increased lifetime (with proper maintenance) compared to other materials. You have the following steps: preparation, installation, applying adhesive, cutting tiles, sealing and grouting joints.
How to install natural stone flooring over underfloor heating?
If the original underlay is from wood, you will need a proper support for tiles. Install it according to manufacturer requirements, for assuring a clean underlay, dry and solid, suitable for the traffic supported by surface tile.
For wooden underlay, a preliminary phase is needed such as building a solid layer for laying the heating pipes, then cladding it with natural stone.
Over solid underlay, you can start installing the heating pipes, according to manufacturer’s recommendation. Usually, the floor is cladded with a thermo insulating material (example: extruded polystyrene) over which pipes are fixed with straps or systems provided by the manufacturer of heating system. Also, install a band from thermo insulating material over room’s perimeter, for preventing the thermal bridge between heated floor and walls. For building the underlay, a screed with special additives for underfloor heating is poured, with thickness specified by installation manufacturer.
After finishing this step, natural stone tiles can be fixed with a suitable adhesive and 10 mm maximum thickness.
General rule is to work from center to the side. Measure length and width of your space and draw a cross in the middle. From this cross, start installing dry tiles with suitable joints (minimum 3 cm), for allowing smooth circulation while using underfloor heating. When using different size joints, grout is variable and the degree of variation can be controlled before starting the installation procedure. When installing tiles with variable thickness, the thickest tile should be install first, because it is the reference for flooring level. Make sure you do not have difficult cuts that require adjustments.
Always make sure you have a perfect look flooring, when entering the room. Because natural stone tiles are slightly different, put aside tiles you are not using in the center, for later installation around edges.
For reducing tile displacement, which can lead to cracking and/or detachment, leave a small area around corners, minimum 6 cm width. This space will be filled with suitable grout. Flexible like silicone, for allowing tiles displacement (if you have floor plinth, this space should be left free).
Install the tiles with a flexible adhesive, enhanced with polymers, such as Weber Set Porcelain. Adhesive color to be used depends on tile color and used grout; for example, when installing natural stone tiles with color variation close to cream, use white adhesive, based on white cement to prevent development of grey stains over the tile surface. Add adhesive in clean water and mix according to instructions, until obtaining an even consistency.
Use a grooved trowel with teeth, keeping it at an angle of 45° when applying the adhesive in the installation area. Practically, you need to develop parallel ribs, which will act as underlay for tiles. These ribs are shaped with a steady twisted movement, for levelling the ribs of adhesive and producing a steady 3 – 4 cm adhesive bed underneath tiles.
It is recommended to work on small areas and remove fresh scraps of adhesive from the tile surface. For travertine that might have cracks on the lower side, we recommend to apply adhesive on both the tile and the underlay.
For a professional installation, apply adhesive on both underlay and tile.
Important! Do not step over tile surface, before adhesive is dried. Allow it to dry for 3 hours (for adhesives with rapid fixing) or even 4 hours (for a standard adhesive).
Read also the continuation of this: cutting tiles, sealing and grouting.