Basement Glass Block Replacement Installation
Hello Everyone,
I am an experienced DIY-er hoping to leverage some expert knowledge for a window installation. My recently purchased home is from 1955 with a block basement. I would like to replace all of the the basement windows (below grade, inside a well, no egress currently or needed).
I ordered one preassembled glass block window from Lowes that is slightly smaller than the wall rough opening. The instructions that came with the window are pretty self explanatory but they do not touch on three questions that I need to resolve.
1. Is there any prep on the existing block that should be done before mortaring the windows in?
2. The top of the rough opening is not masonry, but is instead the sill plate of the house. Can/should I create a mortar joint directly against this sill plate, or should I be prepping this somehow also?
3. This is my most pressing concern and question. The bottom of the rough opening has been raised and tapered to a point of sorts. I believe this may be called a cap? Please see attached photo. The top of this cap on the flat is no more than 1″ or so wide (the metal frame of the existing window sits perfectly flush on the edges of this cap. The new glass block window, however is 3″ thick. So at this point, if I install the window without altering this cap, I would have about an inch of the lower part of the window on both the inside and outside of the that would not look right to me.
At this point, the window is already purchased and delivered to size. I really don’t want to cut part of this cap to create a wider base and reorder a taller window. So these were my two thoughts I was having to resolve this issue:
Install the window with it sticking out an inch at the bottom (inside and outside of the basement opening) and try to create a large mortar joint that will be flush with the window bottom.
Or fabricate a two small forms and affix them the the bottom of the rough opening after removing the old window. I would fill these small forms on either side of the cap to level it out. After it dries, remove them and proceed with the window install.
Any expert opinions would be greatly appreciated.
Thanks!
Austin
Replies
I've only done a couple of glass block jobs - one of them on my own house, and I like how they turned out. Full disclosure: I used to be a mason when I was younger, and only do it a few times a year these days.
Here is what I would do: Prep the opening for the block to fit with a 1/2 mortar joint - so 1" larger than the window you show - both height and width. Your form idea on the bottom is a good one. I'd use Rapid Set repair mortar: https://www.homedepot.com/p/Rapid-Set-25-lbs-Mortar-Mix-04020025/202207958
its made for this type of work. Rapid mean "fast setting" - mix up and get it in place in 5 min or less. You'll be able to set the window an hour later.
Set the window in place, using some shims on the bottom to get it where you want it. I'd cut little pieces of brick, block or dried mortar to get it centered 1/2" all the way around and about 1/4" inset from the outside wall. If it's not even all the way around maybe put a wood wedge in the top to temporarily get it aligned.
Mix up a bit more of the repair mortar and stuff it in a few places around the window (small handfulls). You're basically putting just enough in around it to get it set solid in place. Make sure the mortar is pushed back between the block and the window - don't let it stick out at all or even be flush. You'll cover this up. It will set up quick. Now your window should be solid in place where you want it.
Mix up some type N mortar and fully grout around the window. Once it's set up a bit, strike it smooth and brush it. Here's a training video on glass block: https://www.youtube.com/watch?v=mvKIASX5QMY&ab_channel=MikeHaduckMasonry. I would use a grout bag to get the mortar in.
https://www.homedepot.com/p/Anvil-Grout-Bag-57542/300997951
The type N will go against the upper sill fine. You may get a hairline where the wood and mortar meet over time - caulk it with poly if needed.
Best of luck to you.