What am I looking at and how shall i fix it?

[frustin]

It'll probably be about an inch thick when hacked back to the blockwork. A 2kg tub is more for really small patches. You can get a 25kg bag of hydrated lime for around £20, and make a tub of lime putty with the rest for future use. It will keep for years with a bit of water on top.
I'd guess you need about 10kg of plaster.

if you look at the pics i'm not hacking all that cement back to brick. Just going to chip off the gypsum (pink mortar).

 

[frustin]

Dimension of this wall is 730x660 (give or take). i dont fancy removing anymore of the sandy stuff.

This is round the corner, you can see in the bottom right, the external render bead (this wall used to be facing outside). Bottom left is a hole (but not to the elements but there's a breeze coming though.



this is a close up of the rusted beading

Close up of the hole

 

[stuart45]

If you've got all that to do as well, a 2kg tub will definitely be too small.
I'd still do what cubist advised, and hack off back to the brickwork.

 

[frustin]

I'm concerned there isnt any bricks behind it on this part, which used to be externally facing before my hallway was built.

Please can you explain why i cannot/should not remove the gypsum and add lime topcoat?

 

[stuart45]

When the top coat fails there's often a problem with the base coats.

 

[frustin]

looks like the stone at this point is flat (the white is from my wirebrush removing the sandy material. No idea what that hole is on the right hand side. I should keep on going, right?

.

 

[stuart45]

Yes, keep going.

 

[Kearn]

Looks mostly like S&C render. From all your images, it appears to be a brick construction, so none of the gypsum, cement, tanking etc should be in there as it will probably be causing issues. Or highlighting other moisture issues by preventing the moisture getting out, hence your bubbling and failure at the surface.

Patching over with gypsum or lime is still a sticking plaster. If a jobs worth doing and all that…