Move over, 3D printed houses. There’s a new game in town, and it is able to use standard concrete blocks to build the walls of a house in just one day. Australian company FBR’s Hadrian … ...

If it’s older than that you might need to do some research or consult a real mason. Scrape out the old mortar. Using a cold chisel, a grout saw, or a joint raker, remove a layer of the old mortar.