The main reason why Gypsum is so light is due to the Gypsum product pounds per cubic feet. Gypsum is mainly packaged in 79.4 pound bags. Each one of these bags holds 1.23 cu. ft. of Gypsum. This means that per volume Gypsum in powder form no sand or water added eguals on average 61.5 pounds per cu. ft. and Portland Cement in powder form weights 94.5 pounds per cubic foot which makes it about 2/3’s the weight of Portland cement. Then we blend our sand which weights around 100 pounds per cu. ft. and water by volume which weights around 62 pounds per cu. ft. Please keep in mind that sand naturally has voids in it that water and cement will fill and sand also absorbs water which also makes it heavier then it’s base weight of 100 pounds. Ultimately the result of this mixing of Gypsum, Sand and Water results in a volume of 2.5 cu feet per mix which when still wet weights 118 pounds per cu. ft. However since the Gypsum does not remain in wet stage long, by the time your ready to install your finished flooring the much of the water used to mix your Gypsum has evaporated in the air leaving you with around 96 pounds per cu. ft. Now if you compare this weight to Portland based concrete with sand and stone which weights on average 140 pounds per cu. ft. depending on Hydration, you will see that Gypsum Underlayment weights 2/3’s of what Portland Mixed Concrete does.
1.5″ of Gypsum weights 14 pounds Wet and 12 Pounds Dry per sq. ft.

When we first pour the LEVELROCK RH Radiant Heat Floor Leveling Underlayment over your floor at 1.5″ average depth which will provide the minimum of 3/4″ coverage over the top of your tubes it will weight around 14 pounds per square foot. However after you ventilate and dry the floor sufficiently to receive flooring the weight to due to evaporation will be closer to 12 pounds per sq. ft.

Floor Deflection has a large impact on the depth that is required at a minimum. However the standard rule of thumb applies in 95% of case’s.

Radiant Tubing – Minimum amount above the tubes is 3/4″
Acoustical Board LEVELROCK SAM N12 1/8″ Mat – Require 3/4″ of topping
LEVELROCK SAM-N25 1/4″ & N40 3/8″ Sound Mat – Require 1″ of topping

Marino / Ware and Dietrich Corregated steel decking – Requires 1″ above the high point
3/4″ T & G Plywood Subfloor require 3/4″ minimum of topping
Concrete Slab or Precast Concrete – Requires to maintain a minimum of 3/8″ but may be featheredge at the high point or door ways.

I will give you the facts so you come to your own conclusion.

1. Thermal Mass – Both Gypsum Underlayment & a Mud Job have high thermal mass however because LEVELROCK is mixed in a wet form it doesn’t have the air voids that are found in Mud Jobs thus resulting in better transfer of heat.
2. Reinforcement – LEVELROCK RH Radiant does not require reinforcement unless a moisture barrier has been applied that impedes bond. Mud Jobs always require a moisture barrier and wire reinforcement because they are mashed into place and have not enough water to make a bond to it self let alone to the subfloor.
3. Installation – Because the materials are mixed and pumped in, LEVELROCK RH Radiant type products will use less man power and a fraction of the time to install. Mud Job Requires mixing Portland and sand together with little water then since it is not pumpable it must be man handled to the area that is to be installed thus shutting down your project for extended periods of time instead of the single day typical of LEVELROCK Installs.