For the thinset key coat in an Earthaus Tadelakt shower installation, use a modified thinset mortar that meets ANSI 118.11.
What qualifies
Any modified thinset meeting the ANSI 118.11 standard — check the bag or product data sheet.
Common examples that qualify: Custom Building Products VersaBond and Schluter ALL-SET.
Older Earthaus specs referenced Laticrete 257, which has been discontinued. Any modified ANSI 118.11 thinset is the current replacement.
How it is applied
The key coat is a 1/8" layer applied with a V-notch trowel over the waterproofed substrate (rigid 1/2" backerboard with an ANSI 118.10 waterproofing membrane).
Allow it to set fully before beginning the Base Plaster coats.
For the complete substrate build-up, see the Tadelakt Installation Guide.
Questions? Email support@earthausplaster.com or text 1-800-917-2414.