My thoughts -
As steve said, it's not a good idea to skim sand and cement the same day , as crazing is likely. However, a suitable additive will allow you to do so - Remtox was one we used some years back .
It's also not good to do any plastering on to a solid bone dry background, as the plaster/render will dry rather than set, so wetting it down is needed.
Now, I'm not sure about the day rate/ price issue on this one
He is really giving you an estimate of two days. What other quotes have you had from tradesmen whose work you have seen?
If he has to make two visits, then he is entitled to look for two days money ie he could be elsewhere for two days making the same or better money.
It's up to you whether the job is worth that.
From a repeat business point of view he might be more sensible to say -
- Day One Knock up the render and float it - perhaps allow 2 hours by the time you set up, tidy up, etc. I can do this in an evening before hand, I'll try to see if i can do it after an early one on another job. (I can also prep the wall to skim while I'm there)
- Day Two - 20m2 of a wall to skim - 4 hours is plenty to allow setting up, tidying and so on.
The job to you is only 'worth' one day's money.
The job to him might 'cost' two day's money.
He will have to balance making what he can off one job at the risk of no recommendation, you have to balance how much you need the job done without the benefit of other quotes.
I would say - agree a price, if he says he needs two days, ask him if he can allow for the fact that it will be two half days. If he insists on day rate ,He should be able to tell you the max it will cost, and what conditions will make it min/max time. EG there is an upper limit , it won't take 3 days!
If he skims it the same day, tell him that you will hold 50% until you are sure it has not crazed and will pay him the following week.
