Recently tried to hang a big traditional 3 column rad in an old stone cottage. Wall was lime plaster on top of stone. Of course there was no solid stone behind the exact point that I needed for the rad bracket, just a large void between stones. Bought a Rawplugs resin kit, never used one before. Despite the instructions being poor and the kit being expensive, it was brilliant. Simply embedded a threaded rod into the resin which completely filled the void. Solid as a rock, excuse the pun. Certainly got me out of a hole - excuse second pun. Despite the cost it saved me hours of work and no worry about the rad coming away when it was filled.