Expert: Dan Griffin - 9/18/2009

Question
hi dan i want to cut some windows into a cinder block wall what in the best way to cut the holes the building has headers in place.

Answer
Eric, it will be relatively easy if it is a stack bond install.  If the header was in place, perhaps it was layed up with a future window in mind.

Here are some consideratons:

The header sure does help.

Block walls usually have horizontal and vertical slushed cells every 4 feet with 2 #5 rebars in the cell.  If you encounter one of these, be prepared to deal with and cut the steel.

If it is running bond, you will need to decide whether to remove full blocks and tooth back in with the proper size cut blocks or cut completely through the wall.  YOu can do a reasonable job of slicing into the block webs with a dry diamond on a circular saw cutting from each side.  There will lots of dust.  If you decide to remove full blocks, you will need to cut the mortar all around the block on both sides as deep as possible.  Take the block out in pieces, not full sized, so that you can avoid spalling or damaging the good block remaining in the wall.  

Have a temporary closure in mind for the hole.  I assume you are ordering or having a window built that works out to block dimensions once the hole is established.

It is possible to rim the hole with lumber and trim out both sides, but this will probably not be like any other windows there now.  Old cement block windows were steel sash set in a groove in the block that would be extremely hard to duplicate.  New work has the mason create smooth sides and top with a sill block or slushed cell at the bottom.  Aluminum fixed windows are quite common.

Feel free to ask more if I've not made myself clear.