Rough Cast over Pre-Scratched wall

[Mark 9002]

I've got approx 30ft of wall right outside the Patio door that was put up a lot of years ago. The wall was scratched as shown in the Photos. I know theres a real skill involved with rough casting a wall but I want to have a go anyway .Could somebody help me with the following questions
1 Will it be ok to render over this existing scratch coat after its had a good power wash ?
2 Do I need to apply any bonding ( SBR) to the wall prior to Render. I've heard conflicting views on this as it can effectively seal the Scratch coat and prevent any suction the render may need to stick.
3 what ratio mix do I need for the Render and any additives needed. Does it need to be soft sand or builders sand ?
4 Do I apply the Dashing chips straight away or does the render have to set up a bit first.
My Finances dictate that I have to do this myself as Builders in my area are crazy busy so are quoting crazy prices for small jobs just now. If I'm successful with this this wee job I may have a go at the house front wall
Any help/ advice would be appreciated

 

[Alastairreid]

Dampen the wall down before applying the top coat, no sbr or pva.
Use K- rend it comes in ready mixed bags and a choice of colours just add water.
Coat a manageable area then double back..hit the edges first and cast in panels filling in as you go...if you hit it too early it will slump, too late and the chips bounce off. Practice makes perfect as they say...Good luck...

 

[Mark 9002]

Thanks. If i decide to use K-Rend exactly what product is it I need. I've been on thier website and theres a lot of different types ?

 

[Alastairreid]

Dash receiver.

K Rend Standard Dash Receiver 25kg

The original polymer modified dashing render.

www.rendit.co.uk

 

[Pharun]

why do you want to chip it, you could just render over it again , flat render is softer on the skin than stone chips if you fall and scrape yourself along it.

 

[Mark 9002]

I guess its in keeping with what's on the House. External walls on the house are dry dashed. Its another alternative though. As long as the K Rend or whatever top mix sticks to the Existing old scratch coat

 

[Pharun]

4:1 render coat should be fine, the top coat should not be stronger than the backing coat but you have no way of knowing the strength of the mix already on the wall, I personally would make sure the surface is sound and reasonably clean and apply a thin scratch coat onto the wall , this is done to even out the suction before you apply the top coat and make it easier to control, once the scratch coat is on set up your first vertical rule (of sand and cement) and make sure it is plumb, then repeat the same again at a workable distance apart, you should then apply render across the wall between the rules just be low the top and just above the floor, and rule them off so if you were to put a level across the two rules it would be plumb, what you have then is a box rule, you then fill in the middle and rule it off, you do the same with the top the bottom and sides, you will need a wooden or plastic float to rub up the render and fill out any holes or hollows, you do this along the wall ,but keep an eye on the work you have done so you don't lose control, don't over extend. I used to use a wet sponge to buff up the walls at the end, a gentle circular motion leave a nice finish.
tools req
plasterers trowel
wooden /plastic float
a spirit level
a straight edge
sponge
bucket of water
spot and stand
water brush
=
edit
if you dont feel comfortable with setting up sand and cement rules you could fix roof laths along the wall and use them as a box rule ,removing them as you go along,but this method means you would get a very thick coat as the laths are too thick for a render coat , and it could slide off the wall due to its weight

 

[Pharun]

youtube has some videos on rendering, try this vid

Beginners Guide To Rendering…Every STAGE Revealed | MIXING/ APPLICATION/ PERFECT FINISH​