Replace a Vinyl Window with a Smaller Glass Block Window

I am going to discuss today a two-part project I have mostly completed for which not much guidance was available online or in books. Maybe it will help someone out. It will probably allow others to point out my errors, which is OK, too.

Because we wanted to, as part of our kitchen remodel, move our range to a spot in front of the window pictured below, we decided to reduce the size of the window. We were originally going to remove it altogether, but we like the light it provides. Because we wanted a smaller window, and we didn't need it to open, we decided to go with a glass block window. There are two options for GBWs, as I'll call them: ones constructed block-by-block by the consumer, and prefabricated ones. We chose a 32" x 24" version of the latter (yeah, it says "basement window," but it also says it's great for kitchens).

Removing the existing window was fairly easy. It was wedged into the wall opening and apparently only held by two nails (one on each side) and some caulking on the outside of the window, securing it to the siding. I was able to remove it by cutting the caulk with a utility knife and prying the window (frame and all) out with a crowbar. I managed to avoid breaking the window, which was a plus.

The night before doing this, I built a frame for the new window. The actual size of the window was 31" x 23.35", and the installation instructions that came with the window called for using between 1/4" and 1" of mortar between the window and the frame. I split the difference and decided to use 1/2", so I built the frame with a 32" x 24.25" opening. I read somewhere that, since GBWs are heavy, to use a double sill, so I attached a second 2x4 below the one at the bottom of the frame.

To reduce the size of the opening, I planned to, with a friend, install two new studs in the wall opening to hold the frame [see diagram of window framing, with terminology]. Before doing this, I replaced the three boards already there (the two jack studs and the sill) because they were decaying, and I added a second sill here too, for good measure. I also decided to add a 2x4 across the top of the opening, so I didn't have to try to toenail in the new studs to the header using an upside-down motion. I attached the new studs (cut to the full height of the wall opening (minus the new top and bottom 2x4s) to the new top 2x4, then inserted the three boards as one piece into the opening. I also installed two cripple studs underneath where the frame would be going, to further support it. My assistant toenailed one of these in, but this was difficult, so he ended up pounding a nail up through the two new sill boards into the other cripple stud. I then installed the new frame. I placed the new studs based on where we wanted the window to be in relation to the cabinets we planned to install, so the right edge of the window was 55" from the kitchen wall to the right.

Once the framing was installed, it was time to mortar in the window. If you build a window block-by-block, you can buy channels to attach to the inside of the frame to hold the blocks, but with a prefab GBW, you mortar it directly to the wood. First I used shims and 1/2 inch wood blocks between the window and the frame to anchor the window tightly in place with proper spacing all around. My fear during this portion of the project was having the window fall out the other side of the wall while I was trying to secure it, and smashing into pieces, so I nailed an old piece of window trim across the opening on the outside as a sort of safety bar.

For the mortar, I used Quikrete Mortar Mix, which was recommended at Home Depot (how educated the recommendation was, I don't know). I bought a trowel and a grout bag (which is like a frosting bag). The bag did a good job of dispensing a large volume of mortar deep into the openings, but it was hard to squeeze the mortar out of the bag. It was more or less a two-person job; one person holds the tip and directs the mortar while the other person holds the bag and squeezes it. After using the bag at first, we ended up using the trowel and our fingers to fill the remaining space. We mortared around the shims, leaving some space in order to be able to pull them out after the mortar had set a bit.

I received conflicting advice about whether or not to mortar the top of the window; the official directions said to do so, but others said to use silicone caulk instead, because mortar would place weight and pressure on the window from above. I decided to go the caulk route on the top. I inserted several foam backer rods in the opening in order to save on caulk. I cut the tip of the caulk tube so it dispensed a wide bead and went to work, trying to create a smoothish bead. One set of instructions suggested waiting 24 hours after mortaring to do the caulking, so I did that.

Afterwards, I used plywood to cover the openings where the old window used to be, and then covered it with Tyvek housewrap. I bought some siding J channels, which I will use to trim the window and connect it to the vinyl siding. I also bought siding to cover the plywood; I will attempt to integrate this new siding with the existing siding.