The Best Adhesives to Use with Underfloor Heating 

Installing a new floor heating system is simpler than you may think and there are some tricks of the trade that will help make your installation a truly hassle-free experience. In this guide, we’ll explore the best adhesive options to use with your new water or electric system when fitted with a range of subfloors and floor coverings, you’ll discover: 

• Why good-quality adhesives are so important for UFH installation 
• Understanding the differences between adhesive options 
• How to prepare your subfloor  
• The best adhesives for electric floor heating systems 
• Which adhesives work best with water systems 

How do I select the best adhesive to use with a floor heating system? 

As part of the installation process, many underfloor heating systems require a layer of adhesive either installed above or below the system: some systems will require you to use adhesive to bond the system to the subfloor or accompanying insulation material while others may require using adhesives to fit the floor finish over the system. 

Using a good-quality adhesive is important because you’ll want to make sure it can withstand the temperature changes of your flooring that the UFH system will produce. The best adhesives will have undertaken rigorous testing that conform to the European Standard for you to feel confident with your choice. These tests will quantify the level of polymer in an adhesive – the higher the level of polymer, the better the adhesive will perform in areas of temperature change. The adhesive’s bond strength will be tested at 70ºC, which is fundamental for an adhesive used with floor heating and bond strength is usually tested in dry conditions, under water (known as wet storage) and freeze/thaw conditions. Adhesives that do not perform well under European Standard tests have a stronger likelihood of failing when used with underfloor heating.  

What do the codes used for adhesives mean? 

When searching for suitable adhesives, you may come across descriptions on the packaging or websites that may look like coded language. These codes usually consist of a series of numbers and letters which refer to the adhesive’s performance in the tests mentioned above. Let’s take a look at these codes and examine what they mean.  

For the most part, Warmup recommends using either ‘S1′ or ‘S2’ adhesives with our range of floor heating systems. The deformability, durability, and capability of withstanding high and frequent temperature changes of both S1 and S2 adhesives make them perfect to use. S1 adhesives are ideal to adhere an UFH system onto solid subfloors such as screed and timber. Whereas an S2 adhesive should be used with compressible surfaces, such as over floor insulation which will enhance the efficiency of the system. S2 adhesives are also typically recommended to bond the final floor covering to the system itself.  

How do I prepare my subfloor for UFH installation? 

Whether you’re installing an electric or water UFH system, it’s important to prepare your subfloor correctly to ensure that your new heating solution performs at its best. The starting point to a project is choosing the right materials that suit the project specifications: the better the material, the more reliable the results. You should always make sure that you follow the recommended guidelines when mixing your chosen adhesives and when installing an underfloor heating system. Every heating system is installed in a different way, so it is essential to follow the installation manual. 

Before installing any floor heating system, you should clean your subfloors of any debris and dust and make sure that it is level. If you’re installing a heating system directly onto a plywood or concrete subfloor, Warmup Primer should be used. Depending on your project’s requirements, primer may also be required when installing underfloor heating with floor insulation. You can purchase insulation boards to use with our range of electric heaters separately while most of our water systems come with accompanying insulation materials or feature in-built insulation. Our Ultralight UFH Boards should be installed onto the subfloor using a flexible, cement-based adhesive before fitting your selected heating system above. 

Which adhesive should I use with an electric system? 

Electric underfloor heating systems come in the form of either electric heating cables or heating mats. Heating cable systems need to be manually spaced onto the subfloor to ensure even heat distribution throughout the floor surface whilst mat-based systems have a pre-spaced cable attached to innovative matting for speedy installation times. Because these heating systems sit only a few millimeters above the sub-floor and are very close to the floor finish, it is advised to: 

– Use an adhesive with more flexibility than standard adhesives to cope with seasonal sub-floor movements 

– Use an adhesive containing high polymer levels in order to deal with frequent temperature changes coming from the UFH system. 

The DCM-PRO Heated Decoupling System is a popular heating cable system for use with tiled floors. It offers a flexible installation method through its two membrane options: Peel and Stick or fleece-backed. The Peel and Stick membrane utilises a self-adhesive backing to adhere the system to the primed subfloor or recommended insulation material so won’t require adhesive for this whilst the fleeced-backed membrane allows for the use of adhesives. If you’re interested in installing a fleece-backed DCM-PRO over our Ultralight Underfloor Heating Boards, you should use an S2 adhesive for a successful installation. An S2 tile adhesive should also be used on top of DCM-PRO to affix your chosen floor tiles.  

The StickyMat System features a self-adhesive backing so will not require a separate adhesive to adhere it to the primed subfloor or insulation but again, an S2 adhesive should be used on top the system for tiled floor finishes.  If you’re using other floor finishes with the DCM-PRO and StickyMat systems, you can also use 10 mm of levelling compound to cover the system in lieu of tile adhesive. The levelling compound you select must be compatible with electric underfloor heating and must be applied as a single layer. You can find more top tips about installing electric underfloor heating in our informative article.

How do I use adhesives with water floor heating systems? 

Water underfloor heating systems distribute heat through the use of heating pipes installed either within the subfloor itself or within system-specific panels. Water systems are larger and take up more space than electric systems which means that for the majority of water systems, more flexible tile adhesive will be required compared to an electric system. However, the adhesive properties required from the flexible tile adhesive are the same for wet systems as they are for electric systems: 

– The adhesive needs to contain high levels of polymer to cope with frequent temperature changes. 

– The adhesive needs to be flexible in order to cope with movement in the sub-floor without damaging your chosen floor surface. 

For these reasons, the majority of flexible tile adhesives that are compatible with electric floor heating systems, are also compatible with water systems. 

The VLO Ultra-12 Low-build System is a great choice for both new-build projects and home renovations. The Ultra-12 System features in-built insulation so it can be installed directly onto a primed subfloor using an S1 adhesive. An S2 adhesive should be used to adhere the floor finish to the system or levelling compound can be used instead. Looking for more information about installing a water floor heating system? Find out everything you need to know in our expert guide.