Lintels are usually used to strengthen areas of buildings in preparation for load bearing. They can also be used as purely decorative features. Making an opening in a concrete block wall will allow you to bed the lintel in. This way, it will function as an integrated structural support component.
Measure the cross-section of the lintel. Decide what thickness of cement you will need to hold the lintel in place. This will depend on the chosen construction method. Add these additional amounts to the lintel cross-section measurements.
Draw a rectangle on the wall where the lintel will penetrate the concrete. Work to the measurements arrived at in step one. Use a spirit level and set square to ensure the rectangle is true.
Use a cable and pipe locator to check for electrical cables, water and gas pipes in the area. If all is clear, fit a 200 mm (8 inches) masonry drill bit into a hammer drill. Drill a 150 mm (6 inches) deep hole at each corner of the rectangle. The Faculty of the Built Environment at the University of the West of England, Bristol, suggests a depth of 150 mm (6 inches) for lintels.
Hold a brick bolster against one of the pencil lines. Tap it with a hammer. In a very similar job, Bob Vila recommends a club hammer. Continue tapping, to chip the line into the wall. Do the same with the other lines. The drill holes and chip marks define the outer edges of the rectangular hole you need to cut.
Chip away more material by knocking the brick bolster -- or other chisels, as required -- against the concrete block. Keep working until you have formed a rectangular hole of the correct dimensions.
Place a piece of tape around the 200 mm drill bit at 150 mm from the point. This will function as a visual depth stop indicator. Stowell Concrete recommends a stiff mortar mix. Use three parts sand to one part cement.
Wear goggles, strong leather gloves and a mask.