Dating back to the days of the Roman hypocausts, tile has always been the most commonly heated floor covering because of how inherently chilly tile floors can be and the room types where tile is often used (kitchens and bathrooms). In fact, tile is such a commonly heated flooring material that it made up 87.9% of the floors that WarmlyYours heated in 2019.
Perhaps the most evident trend that we’ve noticed in radiant heating over the last couple of years has been the emerging prevalence of combining an uncoupling membrane with electric floor heating cable for installation under tile floors. From WarmlyYours’ sales data, uncoupling membranes went from 31% of floor heating underlayment sales in 2016 (when WarmlyYours first introduced our membrane) to over 69% in 2019.
It seems that this trend extends throughout the industry as a whole for electric radiant heating installations under tile. Currently, there are many different uncoupling membranes for electric floor heating that are produced by a variety of manufacturers, but nearly all of the membranes share some key characteristics such as impermeability, formed channels for holding the heating cable and some way for attaching the membrane to the subfloor (this is commonly a fleece-type material adhered to the underside of the membrane that creates a secure attachment between the membrane itself and the subfloor with the use of thinset).
The growth in popularity, amongst both homeowners and professional installers, for using uncoupling membranes for heated tile floors is due primarily to the benefits this combination provides.
The tile and the substrate it’s installed upon are essentially two distinct layers in a floor. This means that these two surfaces will have different rates of expansion and contraction. The tile is, by nature, a thinner and more fragile material than most substrates (whether it’s a concrete slab or even a wooden subfloor affixed to joists). So when there’s foundational movement in the building or a discrepancy in the expansion or contraction rates between the subfloor and the floor covering, a floor that has the tile directly adhered to the subfloor will see the floor covering fail in the form of popped or cracked tiles.
A good analogy might be if you’ve ever had mud dry on your skin. While you’re sitting perfectly still, there are no issues and the mud is a relatively smooth surface. But once you start to move your body around, the mud begins to crack and flake off.
An uncoupling membrane protects the tile floor because it allows a small degree of movement differential between the substrate and the floor covering. This is typically accomplished by adhering the uncoupling membrane directly to the subfloor. Then the tiles are “attached” to the membrane with thinset — except the tiles aren’t really attached, but are rather “floating” in dovetail-shaped reliefs in the membrane itself. This keeps the tile securely in place on the floor while still allowing for some small degree of movement between the substrate and the floor covering, which ultimately protects the tile.
Another common cause of tile floor failure is due to the formation of cracks in the subfloor, which “telegraph” upwards into the floor covering. This commonly occurs on concrete subfloors, which had an improper moisture content prior to the floor installation. The water in the concrete can expand or contract causing fractures to form and because the slab has significantly more mass than the tile floor, it’s the floor covering that has to give. This can also occur from substantial foundational movement in the form of “settling” if it’s severe enough to cause the slab to crack.
An uncoupling membrane is able to protect the tile floor covering to some extent by both absorbing and dissipating some of the force generated by the crack over a wider surface than a single tile. However, this type of protection does have practical limitations.
One of the reasons that tile is such a popular choice for bathrooms and kitchens has to do with its water resistance. And bathrooms end up being extremely popular locations for floor heating systems (about 61.2% of all rooms heated by WarmlyYours in 2019 were some form of a bathroom). However, the grout lines and perimeter seams in a tile installation can still allow water to seep into the subfloor where it can cause rot for wood substrates or mildew formation in concrete subfloors.
The impermeable nature of most uncoupling membranes makes them well suited to waterproofing your subfloor but they must be used with additional accessories. These typically come in the form of a polyethylene fleece “tape” that can be used with thinset (similar to how drywall tape is used with drywall mud) to create a watertight seal between both adjoining sheets of the membrane and the perimeter joints where the membrane meets the wall. There’s even pre-formed inside and outside corner pieces made of the same material as the tape for added convenience.
Speed of Installation
Perhaps the most pronounced benefit of using uncoupling membranes for the installation of electric floor heating cables is the increased speed of installation compared to the traditional method of installation. In the traditional method, an installer would need to adhere the heating rolls (or mats/cables) to the subfloor and then embed the heating elements in either self-leveling compound or thinset. The installer would then have to wait for this embedded layer to cure before installing the finished tile floor covering, which could greatly extend the project timelines.
With an uncoupling membrane, the installer is able to use thinset to adhere the membrane to the subfloor. Then, they can snap the heating cable into the channels in the membrane and can work from the membrane’s clean surface as they back-butter the tiles to install them. This method allows for most installations to be completed in just a single day.
There are, of course, other benefits to using an uncoupling membrane with heating cables in heated tile floor installations, but this article has covered the primary ones. We fully expect to see continued growth in the popularity of the combination of uncoupling membranes with heating cables for the foreseeable future — particularly as more and more installers become familiar with this combination.