TP wrote:
Electric radiant floor heat. I need to encase this wire in a
lightweight mix to distribute the heat evenly. They suggest a
light weight gypcrete mix. I read a few facts and it looks very
well suited for the hydroic radiant heat systems. I have used
this wire system before in thinset & tile with no problems. This
surface will be covered in a floating wood laminate. Only 150 sq
ft, ½ inch thick. I was thinking of using a cement sand mix
instead of gypcrete. Should I use any additives with it? Oh
yeah, it will be going over an uninstalled concrete slab. They
suggest using reflectix (bubble foil wrap between the mix and
slab. Anyone done this before...?

Bubble foil would be an odd choice. I'd think that it wouldn't have
the compressive strength and the air could leak out over the years.

Look into Wedi board - it's a 1/4" or 1/2" foam panel with fiberglass
mesh on both sides covered in an acrylic/cement coating. Think Durock
with a foam core. It's also recommended by some of the radiant
manufacturers.

Gypcrete or other self-leveling topping is the easiest thing to do in
most cases. The sand mix would be a distant second in my mind. It
would work but it's a lot more work than mixing and pouring. If you do
use the sand mix, latex additive would probably be wise. How thick is
the mortar topping going to be?

R