Why use an uncoupling membrane?
Uncoupling membranes are used to reduce stresses between a building and screed. When a screed is laid, shrinkage can occur or stresses in the main structure of the building reduce impacts resulting in cracking. Putting a membrane between the subfloor and tile can help to avoid this occurring. When installed with flexible tile adhesive, mats and membranes protect the tiled surface when the structure itself and the screed expand and contract at different rates.
New technologies and trends in tiling means that tiles as thin as 3mm are stronger than ever. As tiles themselves change in both size and thickness, traditional methods of installation require a few changes too. We’ve been asked a lot about uncoupling/debonding membranes lately, so here’s our summary of how these layers and thin tiles interact.
Which uncoupling membrane should I use?
Traditional Tiles: For a tile of a traditional thickness (10mm+), a layer such as DITRA25 by Schluter is ideal. Many specifiers are familiar with this product or similar variations with a cavity mat texture, and are known to specify it as a default option for all tiling projects. It is a great option for use with any of our tiles greater than 10mm in thickness installed on screed.
Thin/Large Format Tiles: We’ve checked with the manufacturers of several cavity style uncoupling membranes who have confirmed they aren’t compatible for use with tiles > 6mm thick. The cavities in a 3D membrane can trap small pockets of air beneath the adhesive and create weak spots which don’t allow for 100% adhesion. British Standards dictate that 80% adhesive coverage is sufficient for a tile to be considered fully bonded, but for a large format or thin, 100% adhesive coverage is required.
TIP = We recommend installers butter both the tile itself and the screed with adhesive when installing a thin tile. Spreading the adhesive in long lines rather than traditional arcs means that any air between the two surfaces can escape down the ridges of adhesive when the tile is laid.
Do I need an uncoupling membrane at all?
If you are looking to use an uncoupling mat, stick to a non-cavity style system such as or Mapei Mapeguard WP 200 used with a thin-set mortar.
Provided the installer has completely adhered to recommended screed curing times and thicknesses and the screed is as dry as possible before the tiles go down, an uncoupling membrane may not be required.
All cement and sand screeds and concrete bases are a combination of cement and sand/aggregate and water. Some of this moisture is absorbed in the hydration of the cement but most of the remaining moisture must be allowed to evaporate so that the screed is sufficiently dry to receive the final floorcoverings. The base is deemed to be sufficiently dry when the relative humidity, as measured by a surface mounted flooring hygrometer/probe is 75% RH or less.* A carbide moisture meter or a tramex meter can also be used to test moisture content.
In projects with strict delivery times where speedy install is of the essence, consider a rapid drying screed such as the A38 Ultra Rapid Drying Cement by Ardex which can be tiled over in as little as 4 hours.
For our recommended installation method for large-format, super-thin tiles request a copy of our Shannon Range Installation Guide by emailing info@ecofriendlytiles.co.uk
Explore our Shannon Range of large format, super-thin porcelain slabs HERE
References:
Ardex – www.ardex.co.uk
Mapei – www.mapei.co.uk
Schluter – www.schluter.co.uk
*(For more about moisture testing with a Hygrometer, reference Annex A (normative) – Dampness testing in BS5325, BS 8203, BS 8425 and BS8201).