9 posts / 0 new
Last post
Cutting Glass Block

I have a raised ranch that was built in 1972. The house has undergone several tasteful additions and renovations. In the back of the house I have several angular windows that at one point were converted to glass block and travel in sections from one section of the house to the another following the angle of the roof. Through a recent renovation, I have uncovered the last of one of the sections and I was looking to have someone cut the glass block for me so I will have a consistent look. The blocks are separated by panes of glass vs. mortar. I have not been successful in finding someone in Westchester County N.Y. to cut the glass block without shattering. That said, I haven't found anyone willing to take on the job. Any recommendations?

Re: Cutting Glass Block

I have never heard of or seen glass block being cut.
If cut, the hollow center would tend to fill up with mortar, water, bugs, etc. The strength of the block comes from the complete module.
Possibly solid block could be cut, but they are thinner than standard hollow block and again, I have never seen it done. It would no doubt take specialized equipment that few people would have access to.
If this has been done I'd be interested in seeing a picture.
One way to make it appear the glass block is cut is to step the block to follow the roof slope, the come back and trim out the block to make it appear it is cut. This may not look good, since you might be able to see up inside the block.

Re: Cutting Glass Block

Thanks Ed21. I appreciate your candid feedback and help. I understand the concept of stepping the block to make it appear as though it has been cut, but it indeed was cut on an angle and the edges are not perfect.
There is indeed a glass pane overlay on the outside of the block to prevent the elements, bugs, etc. from getting in. Molding then covers the edges of the glass pane. The inside portion of the blocks are in the kitchen where upon close inspection you can see that they were somehow cut. I had the General Contractor look at it when the kitchen was being redone. He had no idea how it was done before - other than perhaps using a diamond bit blade. He couldn't find anyone willing to cut the blocks. Most felt they would shatter. Thanks.

Re: Cutting Glass Block

First this warning from Pittsburgh Corning-
"Can glass block be cut?

This is NOT recommended. Because of the partial vacuum in the block any drilling or sawing could cause the block to implode. Also an installed cut glass block will eventually form condensation, mold or mildew on the inside. Projects should be planned so that only whole glass block units are used. "

When I need to drill a hole in glass I use a diamond bit, continuously let water flow on the bit, and apply very little pressure. I have never cut glass blocks but you may be able to do it with a wet diamond saw. You can usually rent them at tool rentals. Wear heavy gloves, a welding apron if available and full face protection. Don't rush it. One wrong move and the glass can explode.

Re: Cutting Glass Block


With that kind of warning, cutting glass blocks is sure something that I'd want to do! NOT!!! I can cut alot of wood and hang a lot of drywall to resize an opening before I'd start cutting glass blocks.

Better revise the project plan. Soumds like there may be a flaw in the design!

Good Luck.

Re: Cutting Glass Block

I know this is an old thread, but I felt I had to respond since I was looking for help with this very same question and did a lot of research on it.

First, yes, you can cut glass blocks with a wet saw. I did mine on a small tabletop model with a 7 inch diamond blade. (You can also use a grinding wheel for metal on a grinder, but this takes forever because you have to go very very slow and it also blows glass dust everywhere. I would not recommend it unless you have no other option whatsoever. In fact, I would rent a wet saw before doing this again. I tried it and while it works, it sucks.)

Second, SHOULD you cut them? There are two answers.

Answer one: If you're going to cut into the hollow center, don't do it. It will fill with mortar, condensation, bugs, and dirt. It will also create micro-scratches and cracks that may turn into larger cracks if you live in an area with changing temperatures. These micro-cracks will also weaken the structural integrity of the block, so even a very minimal hit could crack it.

Answer two: If you're shaving an edge to make it fit, then go right ahead.

For my project, my window opening was an old steel frame set into my foundation, so adjusting the frame size was not an option without investing major time and expense. My window opening was 31.5 inches. The 8 inch blocks are actually 7.75 inches, but you also need spacers (mine were an eighth of an inch). In the end, I needed a quarter of an inch to make my blocks fit. I basically shaved off an eighth of an inch from the two blocks that butted up against the sides of the window frame.

All in all, if you're doing more than just shaving the blocks, don't cut them. If you're having trouble with sizing, try to go with a smaller size block with larger spacers and that might help save you a bunch of heartache and unnecessary work.

Myong Krois
Re: Cutting Glass Block

I have never seen it done. It would no doubt take specialized equipment that few people would have access to.

Re: Cutting Glass Block

This is some news to me. I have never seen it. I hope it won’t turn into a mess after cutting the glass block!


I could truly say that this platform has helped me in purchasing latest and stylish windows and doors for my newly designed house.

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.