Mixing Gypsum and Concrete

make sure to insulate under the tubes unless you have very deep pockets

First what are tubes made from? are they coated.

Cement is stronger - but more alkaline in nature better for exterior/damp use.

It needs to be kept damp to cure - needs this and time to harden.

Plaster of Paris (Gypsum) is nuetral in nature but is not as strong and less suitable for exterior work. - . It hydrates with the water used in mix and hardens quickly. Sets fast if not retarded with gelatin

Why mix them with each other? Both can be mixed with sand.

The tubes are PEX (cross-linked polyurethane). The reason to mix in cement is that gypsum does not have enough compressive strength or wear resistance for a floor so mixing with portland helps with this.

There are several companies which produce gypcrete but they are proprietary and you must hire their installers. It is pumped on as a slurry and is self leveling.

once you determine the proper ratio of gyp/concrete, the liquid to powder ratio will determine the strenth of the cured mix.

Make sure you use Heat Pex as opposed to Aqua Pex. Unless you have some special equipment and experience, you will be far better off using an experienced installer such as Maxxon.

You are mistaken about the wear resistance of gyp-crete. It is used extensively for both thermal mass and for fire suppression in apartments and motels. Presumably, you will be installing some type of finished flooring, so it will not be exposed anyway. Even if you wish to leave it as the exposed surface, the product is available in compressive strengths of up to 3,200 psi, consistent with Portland Cement concrete. Further, it is about 2/3 the unit weight of concrete, so you will not need as stout a structure to support it.

Here is a recipe surprising what can be learned from an MSDS

The MSDS does not show any non-hazardous components - does not need to. Nor does it need to indicate the quantity just < or > the hazardous level so be careful. I write MSDSs and one of the things you need to do is to show what is nasty but keep the user uninformed as to the exact formula. The protein present (could be gelatin or any similar eg casein) might be the retardant. The stength will vary with the plaster to perlite ratio. Same as mortar, the cement to sand ratio determines the strength.

Still see no reason for not mixing the two - this is done in some masonry fillers for exterior use.