Schluter (Uncoupling Membrane)
A polyethylene mat installed beneath tile to absorb subfloor movement and prevent cracked tile/grout.
Schluter Ditra is the brand-name dominant uncoupling membrane in tile installation — but the category includes RedGard mat, Strata Mat, and others. The membrane is a thin polyethylene sheet adhered to the subfloor; tile is then thinset directly to the membrane.
The membrane absorbs lateral movement between the subfloor and the tile, which prevents the cracked grout and broken tile that result when wood subfloors expand seasonally. It also provides waterproofing in shower and wet-room applications.
For any tile install over a wood subfloor — and required for any large-format tile — an uncoupling membrane is non-negotiable. Price it as a per-sqft line item alongside thinset and grout.