External rendering- a few questions?

[ABCwarrior]

Hi folks,

Planning to build a retaining wall from dense concrete blocks on their sides, it will be semi-circular, 10m long by 1m high to a 3.3m internal radius. I'd be happy with it at that, but the missus wants a lovely smooth finish to it all so it would need rendered.
Could this be done freehand off the trowel/hawk or would this require considerable experience/another technique? As it's a semi-circle I can't batten it out really if it's to be continuous and smooth?
I'm a stonemason/builder so have a fair bit of experience doing haunchings etc and working with cement, but what mix would be advisable?
If I left the beds and joints slighty recessed after building, wetted the wall prior to rendering to minimise suction could I get away with a single coat?
The wiki section advises plastering sand- how much cement for a durable mix bearing in mind I'm in the highlands? 4:1? 5:1? Should I add a plasticiser of any sort-lime or chemical?

Any advice appreciated!

 

[roy c]

Hi abc you can use a 4-1 mix with w/proofer, Now as you say you are going to build a curved wall, when you have it built get yourself a piece of 4"x1" timber about 6" higher than your wall and put a roundhead nail 3" up from the bottom of the wall and another one 3" down from the top of the wall sunk into the timber leaving about 8mm sticking out.You could put a cross piece of timber screwed into the 4"x1" at the top at 90 degrees so that it rests on top of the wall. Now you have a screed guide, if you hold it to the wall you can pull it along and it will pull your render thru at 8mm deep. You could put a "band" of render about 2" or 3" wide just above the top nail and the same below the bottom nail and pull two bands thru and let them firm up and use them as guides to fill in between. Or you could pull the whole lot thru and fill the nail holes in after. I think one coat at 8mm would be ok or if you wanted you could take it up to 10mm or do two coats the last one being a 5-1-1 mix, then you would have to adjust your nails to suit. I know this is a bit long winded and I hope you get the "jist" of it,

 

[ABCwarrior]

Thanks for the detailed reply Roy, I understand it- so really to get the finish she's looking for I need to be working to a depth gauge of sorts.
Given the thickness- say 8mm as you advise, if I found some flexible strapping 8mm thick by even 15mm wide I could in theory screw this to the upper and lower with some rawl plugs and form the curve at 8mm thick that way, then render it and screed through vertically- remove the timber when set, put on the copings and patch up to them?

Got a better idea, just need to now think of how to do it most effectively!

Thanks again.

 

[roy c]

At least now can play around with ideas and hopefully reach your goal