Glass block windows are a great way to add elegance to your bathroom. Not only are they stylish, but also very concealing. The one trouble is that they can be very hard to install without the right tools and knowledge. This instructable will explain the process!

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Step 1: Fur Out the Window

Since the window's going in, you'll want to leave extra room. Fur out the existing window opening to 2 in. wider and 2-1/2 in. taller than the dimensions of the glass block panel.

Step 2: Nail Stop Blocks to the Window Frame

Tack stop blocks on the inside of the opening to keep the frame flush to the framing. Assemble the frame, then plumb. square it and nail it into the opening with 8d casing nails, shimming as needed.
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The special-order fixtures, fittings, shower pan, tile and glass block panel can take weeks to get in hand, so do the necessary legwork and ordering well in advance. Before gutting the bathroom, check to make sure that there are shutoffs for all the fixtures or a master shutoff for the entire bathroom. If not, buy ball valve shutoffs sized to fit your pipes. Then turn off the main water supply line where it comes into the house from outside, cut the pipes feeding the bathroom and install the new shutoffs right away (see Photo 7).

Disconnect the trap from the tub, remove any clips, fasteners or screws that hold the tub to the wall, and demolish the old cast iron tub with a sledgehammer. Remove the sink and toilet. Turn off the electricity at the main panel and remove light fixtures. Cap the wires with wire connectors. Then rip out the wall finishes and surfaces clean down to the studs and pull out any insulation. If your ceiling is in good shape, use a utility knife to cut the drywall along the edges so the wall materials will separate cleanly from the ceiling.

How to Order a Glass Block Window Panel

To size the glass block, remove the trim from the existing window and measure the rough opening. Subtract 2 in. from the width and the height to allow for the frame, then determine the panel size by counting the number of rows and courses that easily fits into the opening. Glass block comes in 8-in. and 6-in. squares and 4 x 8-in. half-block rectangles. You'll need to choose between real mortar grout joints and clear silicone–joined blocks. We chose the silicone system because we liked the clean, uninterrupted look. Whichever way you go, buy the panel preassembled and banded together as one unit, ready to set into the opening. Remember that it's easy to make the opening smaller by using furring, but it can be an ugly task to make it bigger. When going with mortar-grouted panels, figure each block is 8 in. wide, then add 1/4 in. to both the total height and width. If you're ordering silicone-joined blocks, figure each block at 7-3/4 in. and don't add the extra 1/4 in.

Step 3: Get the Window Ready for Tile

Rip two 3-ft.-long spacer boards at the same thickness of your tile plus 3/4 in. This will cause the window to protrude 1/4 in. past the finished tile surface. Tack them to the sides of the window opening. Then tack two 2x2s into the boards to hold the glass block panel in the proper position while you push it in from the outside

Step 4: Inject the Expanding Foam

Tap shims between the panel and the frame to hold it evenly spaced on all four sides while injecting the expanding foam. After the foam cures, cut away any excess and caulk the 1/4-in. space between the panel and the jamb on the outside of the frame with silicone caulk. Finish off the trim and siding to match the outside of the house.

Step 5: Additional Tips

Converting a bathtub with a conventional window above it to a shower is dicey business, but the result is striking. Order a premade glass block window to fit your existing opening . Look under "Glass Block" in the Yellow Pages or online to find a supplier.

The key to a weatherproof, attractive glass block window both inside and out is to encase it in a custom-built wooden frame (Fig. A) The inside dimensions of the frame should be 1/2 in. taller and wider than the panel itself. That will give you room to adjust and shim the panel exactly and then inject expanding foam between the frame and the panel to lock it into the opening.

To begin, rip the top and side jambs to the thickness of the wall framing plus the exterior wall sheathing. The cement board will lap over the jambs. The windowsill should also be flush with the interior framing, but hang over the outside sheathing about 1-1/2 in. and have a 5-degree slope toward the outside to help shed water. To keep water from running behind the siding as it drips off the edge, cut a shallow groove (or saw kerf) in the bottom lip. Also, remember to flash behind the trim to keep the window watertight. Trim the window exterior to match the house, using caulk to seal between the trim and siding.

It's important to set the panel so it protrudes 1/4 in. past the finished tile surface. That way, a bead of caulk can seal the joint between the tile and block to keep water out of the wall cavity.