Disaster avoidance: Internal sand and cement render on light weight blocks

[MattChan]

Hello!

I have an internal wall that was sand and cement rendered and then skimmed in the 1980s. After some building work I have this area to patch:

Whats the best process to follow on this? Something like:
- Prime with 50:50 PVA:Water and allow to dry
- Another coat of the PVA mix and start rendering when tacky
- Render in one coat with 5:1 Plastering sand : cement with a dash of waterproofer and plasticiser
- Screed off to around 15mm thickness to match existing and allow to dry for a week
- Dampen down and then go straight on with 2 coats of multi finish.

Or is there a more preferred process to avoid disaster?

 

[Pharun]

Hi, you don't necessarily need to PVA the wall , just wetting it down will suffice then a scratch coat and then the floating coat, a good plasticiser added to the mix will help when you come to skim it, I would tidy up the joint line a bit, also if you do decide to use PVA it would not hurt to go over a few inches onto the old plaster as this would make it easier to control the suction when patching in around the joint.
EDIT
don't forget to put some scrim around the joints where it meets the plaster boards ,