How to Square a Concrete Slab

A big part of working with concrete slabs is making sure that they are correctly squared before you commit to pouring the concrete in the slab forms. Everything that is a part of the building is constructed according to the measurements of the slab, so squared slabs are very important.

1. Select any of the four corners to begin in. Down the inside face of the north/south corner, measure down the length of the form that joins it and place a mark three feet from the corner. If measuring the form board that runs north and south that is joined by the board running east and west to form a corner, hold the measuring tape to the board running north/south and measure down the east/west board.


2. Measure at the same corner the opposite direction. In this case measure down the face of the east/west board along the north/south form board that creates a corner with it and mark it at a spot four feet from the corner.


3. Measure from the two marks created diagonally. The measure should be five feet for the corner to be qualified as “in square” and have a 90 degree angle. If the measurement is off then pull the boards in one direction or the other and recheck the measurement. As the boards move the corners will reshape, keep moving the boards until the five feet measurement is met.


4. Repeat the above mentioned steps for all of the corners. All the corners will need to measure 3-4-5. When they all measure 3-4-5 the slab is in square.