Cinder/breeze block repair

[ladiesman020]

What mortar/sand-cement mix or powders should I do on these cracks and too deep electrical chases.
House build 1935. The room is having all the old plaster, hacked off and re plastered with hardwall plaster.
Ideas?
Edit:
I have some sharp sand and cement knocking about. Also I was thinking about this stuff
https://www.wickes.co.uk/Setcrete-Concrete-Repair-Mortar---10kg/p/133777

 

[JohnD]

I use sand and cement mortar as backing coat, because it is cheap, easy to work, and has a long working life. Wet the wall first or it will suck your mix dry (it sets stronger if it stays wet for a couple of days). Apply in two coats because the first one will slump. It is strong and will hold your condit and boxes in place. Press very hard into the wall. With boxes, screw them in place first, and dribble or flick mortar down the back and sides of them to fill gaps. In my current district, walls were traditionally finished with a lime and sand render (now sand and cement) and a hard fine finish plaster skim.

Leave it a few mm below the surrounding wall surface and you can skim smooth with a plasterboard cement or easiplast once it has hardened. A wide filling knife or a plasterers towel is best as you can bridge across the existing finish on each side of the chase. For very wide patches you can rule it off. Do not use enough to form a lump because you will have have all the effort of sanding (or, better, scraping) it off. A plasterers trowel is easier once you have the hang of it. Your tools must be spotlessly clean.

 

[^woody^]

One coat plaster

 

[Deleted member 292770]

hardwall. if you’re using hardwall anyway.