What is the proper thin-set mortar consistency for installing Schluter-DITRA-HEAT?

Using a thin-set mortar that is suitable for the substrate, apply the thin-set mortar (mixed to a fairly fluid consistency, but still able to hold a notch) using the DITRA-HEAT trowel, or other 1/4" x 1/4" (6 mm x 6 mm) square notched trowel. Make sure to follow the instructions of the thin-set mortar manufacturer.