How to install a Glass Block Shower Wall (with step-by-step pictures)

April 24, 2021

Like the mythical Phoenix rising from the ashes, glass block has recently climbed back into fashion again after being consigned to art-deco diners and industrial windows for many years.

The glass block is back again! HEre is how to install a glass block wall in your shower

Its comeback makes good sense, as you can see in this shower. This challenging project shows how practical, yet attractive, glass block can be. When mortared, it makes strong walls that are impervious to water and easy to maintain. Since you can buy glass block in a variety of sizes and shapes, you can custom fit a shower into almost any bathroom. And of course, the transparent glass makes the shower less prominent, brightens shadowy corners. and adds a pleasant sparkle to the room.

Step-by-step process

Outline the shower design on the walls and floor, remove the wall covering, and fit the shower base to locate the drain. Trial fit blocks to check measurements.

Use the shower base to locate the drain and outline the shower design

Double the floor joists under glass block wall when plumbing the drain lines. Add 2x support blocks where glass block wall parallels the joists.
Insert two straight studs into the wall, make them perfectly vertical with a level, and nail them to the top and bottom plates.

Add support blocks and extra floor joists, and also add straight wall studs as well

Build a form (painted yellow and red here) to mold the concrete sill around the base. Make the top even with the base top and level.
Lift the shower base and spread a thick asphalt layer over the top of the dried concrete sill. Then reset the shower base.

Build a wooden form and mold the concrete around the shower base. Once the concrete sill dries, lift the base and spread a generous asphalt layer over the top of the dried concrete

Stack the blocks using shims and spacers to check their fit. Mark the row heights, then continue the marks up the wall at 8” intervals to guide the other rows.

Stack blocks using shims and spacers and mark the row heights on the wall

Nail a top plate to the ceiling joists 1/2" above the top mark. The plate should be positioned directly above the concrete sill below.
Lay a mortar bed on the sill, and set the first row of blocks. Begin with the corner and use spacers and shims to level the first row. Let set two hours.

Nail a top plate to the ceiling and start setting the first row

Mix more mortar and fill the first row joints, using a piece of wire reinforcement to make sure the joints completely fill.
Spread another bed of mortar over the first row and lay wire reinforcement into it. Repeat every other row. The spacers remain in place.

Use wire reinforcement into the joints every other row

Butter the side of each set block and press the next block against it so mortar squeezes out and it fits tightly against the plastic spacers.
Set the corner block last. Spacers don’t fit it, so be sure that it’s level and plumb. Adjust the entire row to fit the corner correctly, it necessary.

Mortar buttering the side of each set block helps squeeze out excess mortar and tight fit two blocks against each other, keeping corner blocks for last

Fasten a steel anchor to the studs with two screws before adding the third row. Mortar hides the anchor. Repeat every other raw.
Tap blocks with a trowel handle to adjust them. Use a straight edge that reaches from the concrete sill to the top plate to keep them plumb.

Fasten steel anchors every other row and use a straightedge against the top plate to keep everything plumb

Fill the concave sides of blocks along edges so the mortar color shows through the block. Attach anchors between every other block in top row.
Pack mortar in joints when it stiffens but before it hardens with a concave striking tool. Break off spacer ends and smooth the joints.

Attach metal anchors between every other block placed in the top row

Brush off remaining lumps of mortar, then buff block faces with a dry towel. Scrub off stubborn residue with an abrasive pad.
Caulk the gaps at the top and sides with silicone caulk, after gluing tile to top plate. Limit joint width to 1/4" maximum in width and depth.

Factors to consider

While there’s virtually no limit to the imaginative use of glass block in a shower, two factors kept us down to earth — our shower had to be simple and water-tight.

Overall schematics of a glass block shower wall showing all its elements and reinforcements

To make sure we avoided leaks, we bought a molded fiberglass shower base (available from home centers or plumbing fixture suppliers) for our pan (shower floor). They come in several sizes, so choose the one that best fits your plan. The other good, though more complicated, option for a leak-proof shower is to build a custom pan using a special liner, concrete and tile. This takes longer and it is not our main topic today.

This project uses two types of specialty glass block — the attractive comer block for the 90-degree angle and the end block for one side of the doorway. Comer block comes in both 6” and 8” sizes, though only in clear and wavy styles.

End block comes only in the 8” size, so the rest of the wall uses 8” x 8” blocks, because you can’t mix the 6” and 8” sizes if you want your mortar lines to align. The end blocks limits choices in another way. They’re 3-7/8” thick, the larger of the two standard thicknesses. So the entire project uses 3-7/8” thick blocks. The slimmer size (3-1/2” thick) would be better to lighten the wall

As you can see, juggling all these glass block options can get complicated, depending upon your project design. To help plan, visit a glass block dealer and examine the sizes and styles you have to work with. That might also influence what size shower base you buy.

Getting started

Without a doubt, building a custom shower is a big, expensive project. You need to buy glass block, base, tile, plumbing materials, etc).

A professional would need about five days to complete all the steps, including plumbing and framing, concrete work, glass block laying, and tile setting. So allow yourself at least 10 days if you decide to do it all yourself. of course, you can hire pros for parts you don’t want to mess with or to speed the project up. This is not a project for a novice.

You might have to adapt your fiberglass shower base slightly to provide good watertight support for your glass block walls. You can cut off the front edge with a jigsaw, so you can support the front with the concrete sill and waterproof it better. Waterproofing is the main principle to keep in mind when you modify a base. Leaks will cause the wood floor to rot and ruin the shower.

Another critical detail is to match the shower base size to the length of the glass block walls. In this design, four 8” blocks along one side (blocks measure 7-3/4 in, mortar joints 1/4 in.) plus a corner block added up to 34” on the inside (38 in, outside, Fig. 1).

As a rule, leave 1/2-in. expansion space between the block and the studs, making the inside 34-1/2 in. wide. The base was only 34 in. wide. To solve the problem and to keep the shower waterproof, slid the base 1 in. out from the back wall studs so the outer glass-block wall lapped over its edge. later. Screw 1-in. tuning strips to the back wall studs before adding backer board and tile.

A final critical detail is to make sure your floor is strong enough. Each glass block weighs 6 lbs., so the weight adds up fast. A standard 4-in. concrete floor would support our shower, but most wooden floors won’t unless they’re reinforced.

You don’t have to double every floor joist (Photo 2), but for a wall this size, double at least two, those that support the most weight. Consult your local building inspector on this point to make sure you provide enough support.

Otherwise your floor will sag or bounce too much and cause the walls to crack or leak.

You have to open the floor up anyway to run drains and water lines, so this is a good time to add joists. Each new joist should be as long as the one it doubles, so you’re sure it has a strong support point on either end. Sometimes they won’t fit easily because of pipes, electrical wiring or other obstructions. Consult your building inspector or a professional carpenter for help if you need it.

Also notice the reinforcement of the floor with 2x10 blocks spaced 16 in. apart (Photo 2). Since the outer shower wall runs between two joists, the blocks directly support the wall above and keep the plywood floor from sagging.

Preparing the concrete sill

The sill extends along two sides of the shower and supports the glass block and edge of the fiberglass base. This project favored a concrete sill as opposed to a wood sill because water won’t cause the concrete to swell and open gaps like wood, should the sill get wet. You can also mold concrete easily around the shower base.

Build your concrete sill forms from 2x material and nail them to the wood floor, leveling them with the top edge of the shower base, even if the floor dips (Photo 4).

Then put a piece of plastic inside the form to keep moisture out of the floor, and pack the forms with concrete. For this job, buy concrete mix in sacks from a home center and mix it with enough water to thoroughly wet it without making it ninny or sloppy.

Be sure the concrete doesn’t lift the shower pan as you pack it. Then cover it with plastic and let it harden for two days.

At that time, you can lift the pan out, spread a thick layer of asphalt (roof patching material) on the top of the concrete, and reset the pan, embedding it in the asphalt (Photo 5).

When the asphalt is dry to the touch, you’re ready to lay the glass blocks.

Laying glass block

Until a few years ago when Pittsburgh-Coming began marketing plastic spacers, only experts could build a project this large. Plastic spacers are incredibly cheap and now make it easier. The spacers align the block faces and maintain 1/4-in, mortar joint spacing as you squeeze the blocks together.

Still, laying glass block requires patience and attention to detail. To keep the walls going perfectly straight, they were built inside a rigid frame with three perfect sides. One side is the level sill. The second is a pair of studs nailed perfectly vertical in the wall (Photo 3 and Fig. 1C). The metal edge nailed over the drywall (Photo 6 inset) is also vertical, so it too acts as a guide.

To find the third side of the frame, the top, stack the first two rows of blocks without mortar, spacing the bottom with shims and other rows with plastic spacers (Photo 6). Notice that you can’t use spacers with the corner blocks. You’ll lay these freehand or with shims. Mark the heights of the first two rows, then continue marking on up the wall at 8-in. intervals. These represent the height of each successive row. Install a wood top plate on the ceiling 1/2 in. above the final 8-in. mark (Photo 7 and Fig. 1B).

This leaves enough room for the top row plus a gap in case the ceiling sags. Make sure the plate lies directly above the sill beneath, using a long straight edge and level or a plumb bob (weight on a string). Later you’ll reuse the straight edge that spans from the sill to the top plate to make sure the blocks stay vertical.

Setting the first row of glass blocks

The following description of glass-block-laying technique will help your wall go up smoothly.

As you read, note the tools (available at complete hardware or building centers) and special materials used — white mortar, reinforcing wire, metal anchors, and expansion strips (available from glass block dealers).

Step One

Prepare about 1/3 of a 50-lb. sack of mortar for the first row, mixing it to a soft, sticky pudding consistency. The mortar should stick to your trowel. Use the white, prepackaged mortar mix from a glass block dealer, because the white shows through the insides of the blocks and brightens the wall.

Spread a 1/2 in. layer of mortar on the sill and set your first row, beginning with the comer (Photo 8). Tap the blocks down into the mortar with the handle of your trowel. and make them all perfectly level with your first wall mark, using wood shims beneath and spacers above.

Laying the first row accurately isn‘t easy, so take your time.

Then scrape off the excess mortar and let the blocks sit until the mortar stiffens, about one to two hours. You want these first blocks to stay anchored and give you a good starting point.

Step Two

Mix another batch of mortar, the remaining 2/3 sack, and fill the first row joints (Photo 9). Then, with the spacers in place, lay a mortar bed for the second row.

Before laying this row, cut special wire reinforcement for the full length of the row with wire cutters and lay it into the bed (Photo 10). Use this wire every second row as you build.

Then lay the blocks, this time buttering (mason’s term for spreading mortar) the vertical edge of each one before laying the next against it (Photo 11).

Add a spacer to the top, and tap the blocks together and down to seat them on the spacers. Set the comer block last from now on (Photo 12).

Step Three

Before laying the third row, fasten a special metal anchor to the studs with two 1-1/4 in. screws (Photo 13 and Fig. 1C). Use these every other row, alternating with the wire. Also install them between every second block at the top (Photo 15).

Laying a glass block wall isn’t quite as effortless as the photos make it look, even with the plastic spacers. You’ll need patience and a good 2 or 4-ft. level to make sure each row rises evenly. A straight edge that spans from the sill to the plate (Photo 14) helps, too, because it keeps the wall perfectly vertical.

For best results, I recommend that you lay half the rows on one day and the last half on a second day. This gives the mortar in your first section time to harden, and makes the wall more stable as you climb a ladder to lay higher blocks. Besides, there’s more to do.

Step Four

By the time you get to the fourth or fifth row, the mortar will begin to set in lower rows, and you’ll need to go back and shape the mortar joints before they harden.

First, break off the ends of the plastic spacers. by grasping them with a wire cutter or pliers and twisting. Then fill the holes and pack and smooth the joints with a special 1/2-in. concave “striking” tool (Photo 16).

After striking the joints, brush excess mortar off the blocks with a soft brush, then buff off the cement residue with a towel.

You’ll find the mortar already beginning to dry on the block faces by this time. But you can’t scrub too hard yet since you could break a block loose. Use a dry, non-metallic abrasive pad.

Step Five

After letting the first section harden overnight, continue on to the top. Use metal anchors at the top, too (Photo 15). These anchors are the only solid connections you make to the ceiling and wall. They’ll flex slightly so the rigid glass block wall can “float,” that is, move as the wood floor dips slightly when you walk across it.

The soft, plastic expansion strip (Figs. 13 and 1C) maintains a 1/2-in. flexible gap separating the wall and ceiling from the glass block.

Step Six

Since the joints at the wall and ceiling will move slightly, they’ll crack if you mortar or grout them. Rather, use silicone caulk to fill the crack where the block meets the wall, both inside and outside the shower. Also glue tile to the top plate (Fig. 1B) and caulk the remaining gap between the block and the tile.

Step Seven

Finally, to make cleaning easier, seal the mortar joints on the inside after giving them about a week to dry. You can use the same sealer you used for the tile grout (available from tile dealers).