Most commercial descalers are solutions of citric acid and should be harmless in copper boilers. Used hot the limescale will be dissolved fairly quickly unless there is a very heavy coating. In that case the trick is to keep the boiler full of the descaler (which will be much more dilute than you wo...

Dave, Permiable concrete is just what you thought. We call it no-fines because we mix cement and large aggregate and leave the sand out. This creates intenal pathways in the matrix that allow the passage of water and it is often ued to surround porous drains where the ground loading is high and a gr...