How to Frame a Doorway When Building With Concrete Blocks

Determine which side of the opening will be the hinge side. Lay a 4-foot level on the floor in front of the opening in the concrete block wall. If the hinge side ends up lower than the knob side, slide wooden shims under the level (next to the hinge-side jamb) to even out the level. Hammer a finishing nail through the shims and into the floor. If you have a concrete floor, use concrete screws.

Lift the door frame into the concrete block rough opening. Position the hinge-side jamb's bottom edge on the wooden shims, if necessary. Hold a level against the hinge-side jamb.

Insert wood shims between the door frame and the concrete block rough opening. Place the shims at the same height as the hinges. If you are not installing a pre-hung door, place the shims at approximately 5 inches from the top, 10 inches from the bottom and centered between the two. Adjust the shims to level the door frame.

Drive concrete screws through the door frame, shims and concrete block wall to secure the door frame's hinge side.

Place a level on the header, or top, jamb. Lift or lower the knob-side jamb to adjust the header jamb. Place shims underneath the knob-side jamb's bottom edge to hold the header jamb in place. If you are installing a pre-hung door, close the door to check that the gap between the header and door is even from left to right.

Hold a level on the knob-side jamb. Use wooden shims to adjust the jamb. Slide the wooden shims between the jamb and the concrete block rough opening. Place the shims on the knob-side jamb at the same heights as the shims on the hinge-side jamb. Drive concrete screws through the jamb, shims and concrete blocks. If you have a pre-hung door, check that the gap between the door's edge and the jamb remains even from top to bottom before you screw the jamb in place.

Drag a utility knife blade down the shims where they protrude past the door jamb, thereby scoring them. Bend the shims back and forth until they break off at the score line.