$HTSC Once all of the large foam blocks are in place for a wall, builders will place steel rebar throughout the structure before pouring the concrete so that it provides the strength that is necessary for the building or project in question. Each unit interlocks with the other so that you can stack them together with little effort. You don’t need mortar to finish the project either because the concrete works to keep the items in place without any help. Since this structure absorbs shock exceptionally well, it becomes a useful tool in high-risk areas around the world.