The dome has been covered with Vitcas Heatproof Screed. Those 4 tubs i had to buy earlier because they are not supplying enough materials. I used just over 3 tubs to cover my dome in an inch of screed.
For the third coat I tried something different....
For the finish coat (3rd external cement layer) I don't use lime. I use a 4-1 Sand cement mix but add a mixture of Bostik Cementone Waterproofer as the water. It said 30 to 1. I put enough to cover the bottom of a bucket in 2 CM of liquid and filled the bucket with water.
The plus side of using this waterproof seems to be that it is waterproof but breathable so any water vapour should escape but water should not penetrate.
B&Q sell only 'Mastercrete' cement, that's what I've been using.
Mastercrete cement £4.73 a bag X 3 =£14.19
Bostik Cementone Waterproofer = £ 12.43
Hydralime 1 bag =£7.98
Leith's Quarry - Blackhills
Washed Building Sand 0.96 tonnes =£28.51
Total to date : £ 1777.76