Outdoor rendering mix and advise please

[johnscts]

know doubt a ? which has been asked many times. I have a spar dashed external wall and there is blown rendering (about 6 inches) down to ground level. I have chipped all away to the brickwork. I am going to re-render after I hopefully get knowledgeable advise.
1) do I PVA brickwork first - what mix and would one coat suffice
2) sand/cement mix - do I use a mixture of builders / sharp sand what ratio. DIY Manuals quote a lime type of additive ( does this make for a more water proof finishing ) looking a weather extremes ie heavy rain / frost in the winters.
3) lastly deepening on thickness do I need to do a scratch coat and is PVA needed on all coats
Many thanks in advance a quick answer to the 3 questions kind regards John

 

[23vc]

1) no pva on external rendering just hose it down well to soak it
2) plastering sand it's called here also called soft washed 5.1 plus waterproofer scratch coat, can use lime in top coat makes it float up nice
3) scratch coat normal practice, as above pva doesn't come into this it's not internal plastering

 

[johnscts]

23vc many thanks for your help. I had almost given up on a response. Ok so excuse my ignorance but you say to use plastering sand on an outside brick wall - just to let you know I chipped as much away of the old stuff with some of the brick exposed where it had really blown.
Can you clarify the scratch coat ratio. Then the finishing coat ratio
When you say 5.1 this will be the cement water ratio - what do I use to water proof it (I use Wickes and B &Q all the time. Where does the lime fit in and is that in the mix

 

[23vc]

Scratch coat 1 cement 4 sand plus waterproofer plasticiser (2 in one)
Top coat 1 cement 1 hydrated lime 5 sand
This is just what I do, there is a lot of info on here if you search for render mixes so I'd recommend you read some of the other posts and it should become clearer

 

[johnscts]

Many thanks for that much appreciated. Must admit did'nt quite know where the plasteciser came into the mix. Know doubt the sand for both scratch and top has to be plasterers sand. No mention of sharp or builders sand. I did have a job done a year back and I did ask for a quote to render a complete wall on our adjoining semi and I wondered what their ingredients would be.Again thanks for your advice
Kind regards John