How Is Ditra Mat Secured to the Floor?

Substrate Requirements

• A successful Ditra mat installation depends partly on a solid substrate or foundation. The thickness of an acceptable wood substrate varies by the spacing of the floor joists. For joist spacing up to 16 inches, 5/8-inch thick tongue-and-groove plywood or OSB is acceptable. Joist spacing between 16 and 19.2 inches should have a 3/4-inch thick substrate. If the joist spacing is 19.2 to 24 inches, or if you are installing natural stone tile, which is heavier than ceramic and porcelain, you’ll need two layers of 3/4-inch plywood or OSB. Concrete, even with hairline cracks, requires no additional support.

Ditra Mat Installation

• Mix unmodified thinset mortar slightly thinner than the bag recommends for setting tile, but stiff enough for a notched trowel to leave ridges through the material when you spread it on the floor. A precise water-to-dry thinset ratio is not critical. Place a single layer of Ditra mats on the wet thinset with the orange side up and the fleece side against the mortar, butting the sheet seams together. If the thinset requires a period of setting before you can apply tile, the same setting time is necessary before installing Ditra. Press the mat into the mortar with a flat grout float to make a continuous bond.

Sealing the Seams

• Seams between Ditra mats are sealed with Kerdi-Band polyethylene seam tape, which is bonded to the mats with unmodified thinset mortar. This is necessary for a waterproof installation, but you can seal seams anywhere. Spread thinset on the mats along both sides of the seams, then cover the seams with seam tape. Drag a grout float along the tape to flatten it and force out excess thinset.

Installation Over Radiant Heat

• Install mesh-style radiant heat with thinset mortar according to the manufacturer’s instructions. Once the mortar has cured, install Ditra as you would over any other substrate. If your radiant heat requires a thick mortar bed installation, you can install the mats as soon as the mortar is strong enough for foot traffic.

Installation Over Vinyl

• Although you can install Ditra directly over sheet vinyl flooring, the vinyl must be fully glued. Perimeter-glued and cushioned sheet vinyl allow too much movement. Strip or lightly sand the vinyl to remove wax and oils. Although most Ditra mat installations use unmodified thinset mortar, fast-setting, latex-modified mortar can help increase the bond with vinyl.