How to Cut a Window in a Cinder Block

Read the installation instructions for the window that you're installing to determine the size of the wall opening needed. Note that the opening size is not the size of the window itself, since there is also a casement or frame as well.

Draw the outline of the window opening on the cinder block walls using a tape measure and a black permanent marker. When possible, align the window sides on top of the mortar instead of the blocks. If desired, you can create the outline using painter’s tape instead.

Cover all openings to interior rooms using plastic sheeting and painter’s tape. Ensure that all gaps under doors and other areas are completely sealed to prevent the concrete dust from escaping.

Don proper safety clothing before commencing, including safety goggles, ear protection, a dust mask and thick work gloves.

Install a 16-inch-long bit into a hammer drill and create a hole at each corner of the window line until they penetrate outside the home. These holes help you identify the opening from the exterior.

Install a diamond-tipped cutting blade into a 14-inch concrete saw using the manufacturer’s instructions. Screw the end of a garden hose onto the water inlet valve on the saw and turn the hose on at a slow trickle. The water provides lubrication and creates less dust.

Plug the saw's cord in and hold the saw firmly with both hands while you position it over one of the window lines. Squeeze the trigger to cut through the cinder block lines by ½ inch. Continue cutting down the length of one side, then go back to the beginning and repeat the same cut to extend it deeper.

Cut along each of the three remaining sides in the same manner. Then go outside the home and cut each of the lines on that side as well by locating the four holes.

Walk back inside and hit the interior cutout section of the cinder block using a 4-pound hammer until all the material inside the window opening is removed.