Wall chase fill for max strength

[SteUK]

Hi all,

Long story, but I have ended up with two deep chases in a 50mm part-hollow cinder block wall (not load bearing). Want to fill them back in to regain as much of the structural strength as possible. What is best to fill them with? They are approx 30mm deep in places. Mortar? I have some ready to mix patch power and sharp sand. Would a mix of this be nice and strong?

Thanks!

 

[Jameswren]

What's the rest of the wall coated with?

 

[SteUK]

It's an internal wall, bathroom on the chased side, bedroom on the other. 10mm of bonding on the blocks, and a skim of finishing plaster (all be it blown and in terrible condition bathroom side). Same the other side, but plaster is sound and has lining paper on.

Was thinking match what's there...mortar out to the block level, then bond 10mm, then patch up the finish skim. Probably going to cement board the whole room prior to tiling so finish doesn't matter so much.