That's not just an appalling double negative,

I'm building a wall in the kitchen. God what a mess. Dust everywhere. But the main part of the wall is vertical flat, horizonta. All pretty good for a hammer-chewer.
But there is also a small return, and that was not as square as it should be. Unfortunately, I did not realise that a block had moved untill it was too late. It's out by about 6mm over 0.5m, so not trivial.
I started to try to grind it back, but there was too much mess, so I chipped of ffrom the block I had started to grind, then knoked away the two above it and re-laid them. The result is a corner that is a bit scruffy, but essentially square and true and once it is plastered it will be perfect.
The main downside of today's travails is that I mixed a bucket of gubbins, and it went off before I could use it. Bummer.
But at least I do have a square corner. Some sort of fix.
S