Dpm and screed

[JOHNBOY42]

A friend of mine has bought a house where the garage was getting converted in to a room, anyhow the previous occupier has laid all the hardcore down about 50mm below the intended level but we could not find any dpm ,could we still put a dpm then screed about 50mm or do we have to dig out and put the dpm lower?
Also I have read that the best mix for screed is sharp sand 4-1 mix but it did not mention any additives,do we need any?
Also the floor is 8ft x 16ft shall we do this all in one go or section off into smaller sections as this would possibly be easier.

 

[noseall]

i would not like to screed a floor with 1200 gauge dpm below, particularly at only 50mm thick.

4:1 will be ok for the screed mix, you can add chicken wire reinforcement or fibre binders, but we rarely do.

bite the bullet and lay it in one hit.