Liquid Screed Max thickness

Hi everyone,
I was planning on having a liquid screed over my underfloor heating pipes and had in my head a nice 75mm thick design (to retain plenty of heat).
My design is 110mm concrete, 100mm insulation, 75mm screed.
This was to create a fairly level threshold through rear bifold doors

I’ve since discovered though that Anhydrate/liquid screeds have a maximum thickness (55/60mm seems to be commonly referred to) but I can’t find out why this is?
Is it because the curing time would be stupidly long, would it make the UFH less efficient, some other reason?
If anyone’s knows it would be really helpful.
Hoping it’s just drying/curing time as I’ll have plenty of time prior to covering (around 4 months)
PS I know traditional sand and cement would be ideal at 75mm so not looking for solutions but instead, err education I guess!
Cheers

Why not have 120mm insulation -that would give you increased underfloor heating efficiency and will work with liquid screed.

I think that would give you a better saving than increasing the screed thickness to gain more thermal store. The efficiency of in screed systems depend on your lifestyle, more thermal store is not necessarily better.

You could use mapei top cem instead of cementitious screed, or other similar product rather than a liquid screed.

Thanks notch7.

Yes it’s probably cheaper to increase the insulation thickness than the screed.
Had I known about this ‘limit’ I’d have gone thicker on the concrete slab which would have been cheaper still.

So just left curious about why it’s limited at 60mm. Can’t find anything on tinterweb

I can't imagine there being any theoretical max thickness.
As already stated just stick 25mm of eps under your kingspan (or whatever), it's only £5 a sheet.