Thanks! Sounds like solvent free grip fill is probably the way to go! I probably have some heavy furniture to use to prop some batons against, but will probably put a few plugs and screws in the wall as well to try to help it along. Do these screws need to go all the way into the blocks, or are plasterboard plugs going to be good enough? Also, just looking at the reviews on screwfix - the no nonsense solvent free grab has more (and slightly higher rating) than grip fill solvent free - is this worth a go, or would you stick to branded?