In a preferred embodiment, a floor crack isolation system includes a membrane and a deformable adhesive. The membrane includes a basemat, having at least three plies, a ply of a meltblown polymer sandwiched between two plies of spunbond polymer; and a flexible coating applied to the basemat, the coating having a cementitious hydraulic component, a polymer comprising a water-soluble, film-forming polymer; and water. The finished membrane is flexible and is bonded to a subfloor with a deformable adhesive. A method of making the floor crack isolation system includes obtaining a coated, three-ply, flexible membrane and applying it to a subfloor with a deformable adhesive.