This was one of those situations where you have a great idea, check if it’s already been done and find out that there’s a fantastic company – soluform/hoben international who already do it really well. 

Their patented pre-filled concrete sandbags have a inner lining that degrades when wetted by the rain so the dry mix goes off once you’ve put it in position. You bang metal rebar staples through multiple layers at a time to give it strength.

It’s not the fanciest look but I’d argue nicer to look at than unrendered block work and it’s very quick to install so it keeps labour costs down. 

In time the Hessian will rot away and the concrete form of the bags will be left. The first time we used these in Gravesend, Kent, it was at the bottom of a very steep hill that needed retaining next to a busy road with no room to use a mixer, no power or water. These were the choice because they will outlast and wooden retaining work. The next time was at an industrial site in Erith where speed was more important than looks anyway and again they were just the ticket!