Smooth Render mix

Greetings.
I am a time served plasterer (C&G in 1980) who largely left the trade years ago (When you plastered the grey side of the board and we hardly used lime, aside from running cornice...) I am going to 2 coat render and float my front garden wall. I am ignorant about the addition of lime. I would have previously mixed 4-1 sand to cement. Whats the mix with the addition of lime and what kind of lime should I buy?
TIA

Hydrated for a garden wall

Treat it as another cement addition (when calculating)

So you wouldn't do 4-1 and then put lime in.


5s -1c- 1l is about as strong as you want to go (as that is 2 binders in the mix)
Any more lime/cement and it's more prone to plate cracking (small squares of cracks).


Remember start strong (mix) and work weaker towards your final coats, definitely not the other way!

Thank you. I am aware of the pitfalls of too strong a mix.