Why do people charge so much for floor screeding? I've got about 90m2 of 65mm screed over 60m Kingspan insulation — I am not fitting underfloor heating —and I thought the only quote I've got of £1350 seems quite high if, in theory 2 men can do the job in a day, then they are getting £800+ in labour!? I've had a couple of local plasterers come and look at the job and they didn't fancy it when they saw the big expanse and recounted various tales of problems with cracking and settling of levels! They said could you not just concrete it and then put on a finish with self-leveling screed!?
My "time taken" tables suggest that 65mm screed takes around 25 mins per m2. This, in turn, suggests a labour rate of around £8-£10 per m2, on top of a materials price of £4.50 per m2. This would suggest your quote is close to the market rate.
Normally screeders work in a 2 and 1 gang so this 25 minutes figure includes a labourer to mix the screed on site. My latest benchmark house has a ground floor area of 55m2 and the screeding was done in 3 man-days, which is spot on 25mins per m2.
However, you do see people getting screeding done at apparently much faster rates. How come? Well one obvious issue is quality. A good screeder doesn't hurry - it's an art that not many people do well. Also, supplying readymixed screed can make savings - you would loose the labouring costs and get those 25 mins down to around 18 mins per m2 - but you would of course be adding to the materials cost.
The overall time taken is also affected by whether it is a large space or lots of small rooms. Large spaces are quicker to lay but, as your plasterers point out, they are not without their problems, esp. if you are laying underfloor heating in the screed. BS EN 1264 recommends that you limit the area to be screeded to 40m2, or 8m lengths in any one direction. If you exceed this, you should separate the floor into bays divided by some flexible expansion material. You can generally stop cracking by using mesh or adding fibres to the mix but on very large areas you may find that the screed has a tendency to lift up due to expansion.