US Patent 7617647 Underlayment for tile surface

Fiber-reinforced pultruded planks serve as underlayment for tile, stone or terrazzo. In one embodiment, the planks have a thin base surface with a plurality of elongated ridges. The planks have interlocking tongue and groove edges. The elongated ridges have a narrow base and a wider distal portion wherein the areas between adjacent ridges have a trapezoidal cross sectional configuration with the thin base resting on the support. Tile can be adhered to the surface using a rigid cementitious adhesive which fills in the trapezoidal area, creating a very rigid support structure. If the planks are reversed with the ridges resting on the support, tile or stone can be adhered to the relatively smooth thin base with an epoxy adhesive.