Small professional home recording studio in Italy

[Syncamorea]

You wouldn't have to demolish the entire wall to remove the sand. You could drill out a few bricks here and there and hire some help to blow and vacuum it out. It will be messy but worth the effort - look for a local contractor with an industrial high capacity vacuum. Hell, they can vacuum prairie dogs right out of their tunnels so sand is no biggie. Filling the brick wall voids with sand is a good idea if the build didn't block the voids. That's better done one course at a time as you build.

[Demor]

Originally Posted by hsstudio

...will add some heavy anchors where there is more pressure, like the wide side where there is a lot of sand.....

I believe the pressure will be the same at the narrow or wide side. The wide side has a bigger surface to stand on, so the hight of the column of sand determines the pressure not the width.