Generally, featheredge compounds are used to fill in low spots occupying a small percentage of the overall floor area. They may also be used to fill in large depressions. Featheredge compounds are site-mixed, may require primers or reinforcement, and are installed using trowels for spreading and a straightedge for screeding off the excess. The patching compounds you may use for preparing areas to receive sheet goods or wood strip flooring may not be adequate for tile. For best results, single-source the featheredge compound, tile adhesive, and tile grout from a single manufacturer.
The photos used for this article came from a bathroom floor covered with 1 1/8-inch exterior plywood over 16-inch centers. Also included in the installation is an electrical resistance tile warming system. The main reason for using an SLC for this project was to facilitate the installation of rather small stone tiles over the radiant heat mat. I followed the manufacturer's instructions regarding floor prep, mixing, installation, and curing. For this 40 square foot floor, preparation of the floor, and mixing and applying the SLC took about two hours-ten minutes of which was spent mixing, pouring, and distributing the mix. The installation began with a survey of the floor to check for fastener heads that might interfere with the heating mat, vacuuming away the dust and debris, and wiping the surface with a clean, barely damp sponge. Next, I coated the plywood subfloor with a companion latex primer (Photo 1), allowed the primer to dry to the touch, and then installed sheets of galvanized expanded metal mesh to help reinforce the SLC (Photo 2). The mesh covers the entire floor, and is held in place with hot-dipped galvanized roofing nails.
In spite of the name, all SLCs require some human assistance to ensure that the bulk of the material is evenly and quickly distributed. Photo 4 illustrates the consistency of the SLC used on this project, while Photo 5 shows a trowel being used to distribute the wet mix. According to my calculations, this project needed two full sacks of SLC to cover the mesh and heat mat. As soon as I had dumped the first full batch and distributed it over one-half the floor surface, I dumped and distributed the second batch and allowed it to dry and harden overnight. The following day, the SLC covered floor was ready to tile (Photo 6).