Which exterior render?

Chickereeeee

I will be having a rear extension built onto a 1920s house. The house is original, unpainted pebbledash, and I am wondering what render to use. My plan is to render the (block) extension, plus the rest of the rear elevation of the house. I don't want to have more pebbledash, and a would prefer a smooth coat. However, I have seen a LOT of 10+ year old building with extensive staining, which I want to avoid.

Which render type (I assume thincoat) would be best for this purpose?

(At some stage in the future, I may apply EWI to the other elevations, with render to match the rear)

Thanks

stuart45

Are you going to hack off the pebble dash, or render over it?

Martyn_H

I would never pebbledash again. Bits come off every time it rains. 

Chickereeeee

stuart45 said:

Are you going to hack off the pebble dash, or render over it?

Render over it.

ThisIsWeird

Your concern is staining, because you've seen that on numerous new-builds?
Sil's self-coloured render (I understand K-Rend silicone stuff) on a ~2007? build shows this too in places, and some houses on the estate have it bad - rust stains from iron particles, I understand?
Are you hoping to use self-coloured render, or paint afterwards? For the latter option, I was part of a group who painted an old external wall 10 years ago using brill-white epoxy masonry paint; it hasn't been touched since, and looks as good as the day it was applied.

Chickereeeee

ThisIsWeird said:

Your concern is staining, because you've seen that on numerous new-builds?
Sil's self-coloured render (I understand K-Rend silicone stuff) on a ~2007? build shows this too in places, and some houses on the estate have it bad - rust stains from iron particles, I understand?
Are you hoping to use self-coloured render, or paint afterwards? For the latter option, I was part of a group who painted an old external wall 10 years ago using brill-white epoxy masonry paint; it hasn't been touched since, and looks as good as the day it was applied.

Yes, staining in particular. The worst ones locally are blocks of flats and a hotel. There is a YouTube  video which describes the problem:

https://youtu.be/GnzXw8fQhzY?si=F2StLaSVhVQPKHmu

KRend seems to be worse than Silicone render.

The house has good overhangs, but still nervous. Sand/cement seem better in some ways (according to video and comments) but have their own issues.

stuart45

There's pros and cons to all the different methods. Sand/lime/cement render is still a good method of it's done properly. Nowadays a lot of plasterers are more used to working with K rend, which is a silicone render.
When sand/lime/cement was the normal method the plasterers and labourers were more familiar with it. 
It's important to get the correct mix. The top coat should be weaker than the scratch coat. Also the minimum amount of water should be used. After most of the water has been added, it should be allowed to mix for around 10 minutes to get enough air into it. This allows it to be workable without excess water.
Using the correct plastering sand, and not building sand is important.
The scratch coat should be spot on, so the top coat is an even 6mm.