What is a decoupling membrane?

A common question we get asked here at Millcot is – what is a decoupling membrane, or mat, and what does it protect against. In short, a decoupling membrane, also known as a decoupling mat, is used prior to tiling a floor if there is potential for the substrate to ‘shift’ after the tiles have been laid.

Decoupling membranes come in various forms and all are designed to achieve the same level of protection against tiles cracking when the substrate becomes slightly unstable or shifts slightly. The most popular style we sell here at Millcot was originally designed by Schluter Systems and for years has been the industry standard that all other matting systems compare themselves against.  We stock the Alferpro version - https://www.millcottools.com/collections/tiling-products - which has proven to be just as good as the original, high performing, Schluter Ditra product.

It is 3mm thick, has slight indentations on one side (for the tile adhesive to latch onto to) and a fleece back (to enable it to be glued securely down onto the substrate). Other products on the market come in a fleece only form or a fibreglass mesh form.

All types are glued securely down to the substrate with either a flexible tile adhesive or a dedicated flooring style glue, such as Ardex AF200.  Once the matting is glued to the substrate and tiled over it can accommodate slight lateral movement due to the ‘give’ in the matting sandwiched between the substrate and the tiles.

Decoupling membranes can only accommodate lateral movement (side to side) so are generally used in areas that are subject to slight lateral movement.  Examples are: underfloor heating which can cause the screed to swell and contract slightly, screeds with an expansion gap in between them, two different substrates e.g concrete and timber side by side and the tiling needs to cover both substrates.

So, in summary, decoupling mats, or membranes, come in different forms but all serve the same purpose of preventing tiles from cracking when they are laid over a substrate that is likely to shift laterally.