The most common type is called masons mortar, which is used for building chimneys and repairing them. For smaller jobs, pre-mix mortar is available that is used right from the container.
Concrete chimney blocks are 24 inches square, with a hole at the center that is sized to fit a section of vertical ceramic flue tile. Using these blocks makes the construction of a chimney faster and easier and allows it to take up less space than if it were made from conventional concrete blocks. If you are in Buffalo and WNY and need a Chimney contractor, look no further than Buffalo's Best Concrete.