Phil L coughed up some electrons that declared:

Digging out concrete isn't as hard as people imagine - a 15lb sledgehammer
and a good pickaxe will have it in manageable sized lumps in a few hours,
plus a few more hours to barrow it to a skip, then a brisk rake over to
get the extra depth, and if you want to cut a few corners, you can use
75mm insulation and 75mm of concrete, which is more than adequate, which
means less digging, less skip space, less concrete to buy, but as you
appear to have made your mind up, good luck, but I'll reiterate WRT the
floor scrabblers - they don't work


Hi,

I have to admit, I hadn't realised that screed was optional...

Thanks for the good advice. I'm going with the plan I have because I'm
comfortable with it. If I follow every opinion, I'll end up blowing around
like a reed in the wind ;- Sure you can see my position. I don't think
your advice is invalid, but just that I'm not comfortable with it in this
situation. Next time maybe

What I should have done is to research and quantify the problem 6 months ago
to my own satisfaction instead of subbing the whole job to builders who
where far from expert in flooring matters. Given the whole picture, I might
have gone for this solution up front.

However at this stage, I'm not up to concreting (it's 21m2 BTW) such a large
area and I'm not letting another builder in the house (plasterers welcome
though ;- ) - rather live or die by my own hand this time.

Thanks for the good luck - it will succeed...

But - there will be a couple of "next times". One is the shower room floor
and the other is a possible future conservatory. Both do get new floor
slabs.

You mention that screed is optional. But I presume, not, if one is going to
stick wet underfloor heating pipes in? Or can these be buried in concrete,
assuming insulation under the concrete?

Cheers

Tim