Lewis Lupton, ARDEX group national training and technical manager, explains the collaboration the company has undertaken with Polypipe Underfloor Heating to make tiling onto retro-fit board systems easier.
Water-fed underfloor heating systems have been around for decades, though traditionally these were “in-screed” systems were pipes were laid and a sand:cement or anhydrite screed pumped on top.
In-floor, in-screed systems, however, are probably more suited to new-builds. For renovations, whether commercial or domestic, where a water-fed underfloor system is required, retro-fit low-profile overlay systems are becoming more and more popular.
These low-profile overlay systems come in many forms, from gypsum-based systems to XPS foam boards and more. There are a lot of misconceptions and inaccuracies when it comes to the installation and tiling requirements for these types of boards – whether it’s just a “throw a grit primer on it”, or “just use an S2 tile adhesive”.
In-fact it’s far more complex than that, as there are many different board systems out there, each manufactured in a different way and with different requirements.
To address this, ARDEX has teamed up with Polypipe Underfloor Heating to provide a tried and tested recommendation for its gypsum overlay board and XPS felt-topped lightweight overlay system.
Preparation
What is key for all retro-fit board systems is subfloor preparation.
Before installing these boards, ensure that the subfloor is sufficiently dry, flat and rigid, plus free from deflection. If installing onto pre-1970s concrete for example, you must ensure that a Damp Proof Membrane is installed – as any rising damp can cause these board systems to fail.
If the base is not level to SR1 surface regularity (no greater than 3mm over a 2m straight edge), then you may need to level with a recommended ARDEX levelling compound. For minor surface irregularities, a tile adhesive can be used to seat and bond the boards.
Some lightweight overlay boards can also be used on timber. Ensure the timber floor is rigid and free from deflection.
If the floor is not free from deflection it may need to be relayed with additional supports/noggins or over boarded. The floor should be screwed at 300mm centers. Prime the timber with one coat of a undiluted recommended ARDEX primer.
These lightweight boards are particularly common and don’t offer additional deadload on timber floors.
Installation and tiling of gypsum overlay boards
Gypsum overlay boards can be installed dry laid or onto a bedding layer of tile adhesive.
Before laying the boards we recommend leaving a 6mm expansion around the perimeter of the room. Whether dry laying or onto a bed of flexible tile adhesive, the board should be installed in a brick bond fashion.
If dry laying, adjacent panels can be glued together using an ARDEX MS polymer adhesive.
Laying onto a bed of tile adhesive should be used if there are any minor deviations in the sub-floor. Before laying, prime the back of the boards using an ARDEX primer at the correct ratio (1:3 with clean water). Comb out the adhesive and lay the boards into the adhesive, making sure they are fully seated with full contact.
Once the boards are laid, the surface of the boards should be primed (diluted 1:3 with clean cold water), applied with a broom and left to dry.
Once dry the pipes can then be fitted, connected to the manifold and then pressurised as per the manufacturer’s instructions. We recommend installing an ARDEX bonded uncoupling mat using a thin bed of flexible tile adhesive. Using a flexible fibre-reinforced tile adhesive, tile onto the boards directly or the pre-laid uncoupling membrane.
Once the adhesive is dry, grout with a suitable flexible ARDEX grout. After grouting, sufficient time must be given to allow for the adhesive bed/grout to fully harden before gradually bringing the floor up to the recommended operating temperature (5°C per day).
ARDEX systems have been strenuously tested with Polypipe Overlay systems – when tiling to any other retro-fit board systems, we recommend contacting our technical helpline.
Read the full article on the Tile and Stone Journal website for Ardex’s advice when tiling with an XPS overlay board.
www.ardex.co.uk
