Constructional Hearth. Hardcore depth & screed finish?

[lovelyjob]

More on my hearth..sorry guys. New Constructional hearth, 1400mm wide by 900mm into recess.
Overall height required from ground up to level with ply floor is 418mm.
I intend to build a block retaining wall and then fill that with the appropriate materials. Can you advise me on the different depths required please for
1/ Hardcore
2/ Sand Blinding to take DPM over.
3/ Concrete MULTI USE READY MIXED
4/ Screed (if recommended) 3:1 sharp/cement?

Obviously I would want as much Hardcore as possible to keep the mixing down on the others...what would my min thickness's be please.

Do I need to finish the hearth with a screed or will straight concrete be ok. The decorative hearth may not be fitted for a while so the constructional hearth will be seen for a while yet. Will the concrete finish look a little crude, or is this down to the aggregate size. If screeded, should it be bonded to the concrete and with what?.
Thank you all for replies guys

 

[gwernybwch]

Do I need to finish the hearth with a screed or will straight concrete be ok.

Sorry OP I don't know the answer, I was searching the answer to a similar question and came across this thread, so if there is anyone that knows the answer, I'd also appreciate a reply.

Thanks in advance for any replies.

 

[lovelyjob]

any advice please..?

 

[stuart45]

5 inches of crete is enough.