Casting a bracket for a heat pump/water heater?

[P-plats]

Will likely replace the existing heat pump with geothermal heating, and then there will be a water heater as well, but space needs to be made for it.
Today, the heat pump is on a base, and I think it's easiest to cast an additional base next to it instead of trying to chisel away the existing one.
The base is about 20-50mm high and approximately 80x80cm.

How do you best cast this base so I can lay tiles as soon as possible?
Should you use expansion concrete, self-leveling compound, or something else?



The outer blue line is where the base should be, and the inner is the intended water heater (VVB).

 

[P-plats]

Someone recommended Snabbslipsats Weber Weberfloor 318 in another thread, what do you think about it?

 

[Krille-72]

Someone suggested Snabbslipsats Weber Weberfloor 318 in another thread, what do you think about it?

Weber 318 will be perfect. Throw in some reinforcement too. If you prefer to use a self-leveling compound, use a fiber-reinforced compound. If you're not laying tiles or painting the floor, you might as well use regular concrete.

 

[tobbetk]

Why do you need a new heel?
Can't the new VVB stand on the floor instead