I read that alkalis can cause little damage or irritation when they get into eyes initially, but once left for a bit it ends up being too late, and the damage is quite nasty. Eye protection is a must.
On a site meeting on Friday I ran into an old boy builder who had worked on a listed building job I did in Gloucester towards the end of last year. (this guy is in his 70s and still works like a machine)
He was taking great delight in telling the young lad on this site about the historic building and how all the plastering had to be done in lime mortar. "That lime mortar" he said, "brilliant stuff".
Now, when we were on site it was a different story. I remember him saying that lime mortar was a load of airy fairy nonsense and he couldn't undertstand what all the fuss was about. (Actually those weren't the exact words he used but I don't want to offend anyone)
When I pointed this out to him on Friday he put his hands up and admitted it. He thought it was rubbish but by the time he got to the end of the first wall he had changed his mind. At 70 odd years of age he's a complete convert. Any more of those lime mortar jobs he said and I wouldn't mind taking them on.
So, to get to the point, I reckon you ought to be able to get any plasterer to do this at ordinary rates (about £40.00/m²) plus perhaps an allowance for taking a bit of extra care and to keep the work protected and damp whilst it cures. (although you could do that yourself) There might also be some extra material costs.
I suppose it also proves that you can teach old dogs new tricks after all.