Centuries ago, European builders developed a reliable method of installing tile for high-traffic, high-use applications which relied upon a layer of “sand strata” between a structural substrate and a mortar-bed/tile composite top layer. Modern theory explains that the sand strata “uncouples” the tile from the structure, allowing structural movement without damage to the tile layer. However, due to space (height) requirements and other concerns, the sand strata method for tile installation is, for all practical purposes, extinct.
Approximately twenty-five years ago, a modern analog of the sand strata system was developed in which a thin, polyethylene sheet membrane functions as the uncoupling layer. This product, sold under the tradename DITRA, included a grid structure of square, cutback cavities and an anchoring fleece laminated to its underside. This membrane allows the normal loading forces exerted on the tile surface to be widely distributed through a forgiving shear plane, similar to that which would be expected in the sand strata. The resulting affect contradicted conventional theory which suggests that extremely strong bonds are necessary between the tile and the substrate to maintain a crack-free tile surface.
In fact, however, this system illustrated that a relatively weak interface is more forgiving, allowing substantial movement in the substrate without any evidence of cracking in the tile or the grout joints. This system also allows differential expansion and contraction between the tile and the substrate and can be used on a wide range of substrates which have traditionally been viewed as problematic; including plywood, OSB, post-tensioned concrete slabs, green concrete, radiant heated floors, and gypsum underlayments.
A direct, force-conductive bond of rigid materials such as ceramic or porcelain tile and stone is not suitable, since these surface materials are sensitive to tensile stresses, particularly when also exposed to live and dead loads. This fact becomes increasingly relevant since the formats of tile and stone are dramatically increasing in size. Twenty-five years ago, a 300 mm×300 mm (12″×12″) tile was considered very large. Today, formats of 900 mm×900 mm (3′×3′) are commonly used and many modern manufacturers offer large formats up to 1200 mm×3000 mm (4′×10′).
While the DITRA product performs well in many environments, the present inventors have improved on this revolutionary concept.