Chris McQuade of F. Ball advises on retrofitting underfloor heating, focusing on the unique considerations for choosing and installing floorcoverings to boost comfort, energy efficiency, and property value.
The application of a floor smoothing compound is a recommended step as part of any flooring installation to create a perfectly smooth base for floorcoverings and ensure a flawless finish. Floorcovering and adhesives manufacturers also advise basing adhesive selection on the specifics of a particular project, including features required for ease of installation, as well as checking the compatibility of chosen floorcoverings and adhesives to prevent floor failure.
This invites questions such as: “What smoothing compound should I apply?” and “What adhesives can I use?”
There is sometimes uncertainty about the need for a specialist smoothing compound when working over underfloor heating. There are similar concerns around why a temperature tolerant adhesive is required to install LVTs in conservatories, for example, but they are not necessary over underfloor heating.
Myth versus Reality
In fact, when working over underfloor heating systems that are contained within the subfloor, no specialist provisions are required. It is just recommended that systems are turned off 48 hours before the installation of floorcoverings, during and 48 hours after.
The issue comes when working over retrofit electrical wired or water-fed underfloor heating systems that are increasingly installed over subfloors as part of new build or refurbishment projects. In these situations, it is advisable to use a purpose-designed smoothing compound to encapsulate the pipework and electrical wires, allowing between 5 mm and 35 mm of a smoothing compound above the pipes (less for electrical wired systems), depending on the type of system being installed and the manufacturer’s instructions.
New Developments
The rise in popularity of underfloor heating, especially retrofitted installations, has led manufacturers of subfloor preparation products to launch specialist smoothing compounds that are formulated to encapsulate underfloor heating systems.
These products can also be suitable for use over a wide range of absorbent and non-absorbent subfloors, including sand/cement screed, tile backer boards, concrete, plywood, granolithic, terrazzo, epoxy and polyurethane resins, ceramic and quarry tiles, as well as waterproof surface membranes.
Extreme Temperatures
Once the smoothing compound has been installed and the subfloor is ready to receive a floorcovering, it’s not necessary to use a temperature tolerant adhesive unless the room is subject to extreme temperatures caused by solar gain.
This is frequently the case in heavily glazed areas, such as conservatories or kitchens with bifold doors, which then rapidly cool at night. Extreme temperatures or temperature fluctuations can cause vinyl floorcoverings to expand and contract significantly, potentially leading to unsightly tenting and gapping at the edges of floorcoverings, particularly between adjacent vinyl tiles or planks, over time. When the bond has fully matured, temperature tolerant adhesives hold floorcoverings firmly in place in these environments, restricting these movements and ensuring the long-lasting performance of installations.
Temperature fluctuations as a result of underfloor heating systems are much more gradual and less extreme than changes in temperature resulting from solar gain, which can be much more sudden and range up to +60°C. To meet British Standard guidelines of resilient and textile floorcoverings, underfloor heating systems should not exceed 27°C at the bond line.
Where a temperature tolerant adhesive is required, there are a number to choose from, including ones with extra features, such as pressure sensitive characteristics.
Further advice
For checking the compatibility of chosen floorcoverings, as well as suitability for use in high-temperature environments, F. Ball produces its industry-leading Recommended Adhesives Guide. The 2024 edition of the guide lists adhesives recommended for use with over 6,000 floorcoverings, produced by over 200 manufacturers.
Chris McQuade is technical service officer at F. Ball