Masons are in the business of laying bricks and concrete blocks. They use several simple tools to check that their work is level as they mortar the masonry into place. The most common tools are called blocks and twigs. The blocks are small wood blocks and the twigs are pieces of wood or other material about the size of a Popsicle stick. The block has a ledge that fits against the end of a row of blocks with a string attached. The twig attaches to the string and is held even with the top edge of the block by a loose brick. The second type of alignment tool is a masons stretcher bar. This adjustable tool looks like two metal bars with ears on them. It is held in place by the tautness of the string.
Select a set of masonry stretcher bars that are easy to adjust and use.
Adjust the depth measurement (between the ears) on the stretcher bar by loosening the nuts and sliding the bars. Place the tool from the front to the back of the type of block you will be laying. The tool depth is set slightly more than the depth of the block. You should be able to easily place the stretcher on the block and move it as you move along your course.
Set each stretcher bar at the same measurement. Attach the stretcher bars together by attaching string to each bar three-quarters away from the side closest to you. This will allow you to tighten the string by twisting it around the stretcher bars. The string should be long enough for several feet of block or bricks but not so long that it sags in the middle.
Wrap the string around each stretcher bar toward the front. This is usually three to four wraps. The working wrap should cross over the top of the stretcher bar and rest in the corner between the metal ear and the top of the stretcher bar. This means the string will wrap in opposite directions for each bar.
Place the stretcher bars string width apart. Pull the string up and over the stretcher bar if the string is sagging. The taut string will place a strain on the bar and pull it at an angle toward the string center. This strain holds the bars in place. A correct string will be level and taut between the bars as well as align with the face of the block being laid.