Hi all. From previous advice I see a sand cement render on my internal block will give an airtight layer (along with tapes at windows and floors etc). It is also the finish I want on the inside . 
Is a 10min layer of sand cement ok or do u need to go the scratch coat , finish coat layer?. Painting will seal it nicely I hope.

also , would the cost of internal plaster be cheaper than plasterboard and skim ?

thanks

 

S&C will seal the blocks You will more likely be 15 to 20 mil thick 

Put on in two layers on the same day 

You will need to use river sand 

which should be a little cheaper than boards 

But the Labour will be more expensive Not a job for a novice