Radiant heat and new flooring

[Ernest Ekberg]

My son did the radiant heat. You have to router a route for the heating cable in the plywood. Cover that with a skim coat of Portland based patch. Then adhere with urethane adhesive.

[D. Troit]

Understood, Thanks.
Your attached photos "look" like MDF or untempered hardboard was used as underlayment, and the wires covered with silicone caulk.
Routed plywood and Portland patch sounds like a good approach.
Have you done others?

[Ernest Ekberg]

This underlayment was used after the old tile and mastic was removed. I haven't done anymore, as this is an expensive and time consuming add on.