Installing Glass Block – Tricks of the Tradesman

Installing Glass Block – Tricks of the Tradesman

You can install glass block!

It’s not the easiest do it yourself project out there, but it will be perhaps the most rewarding, because it can be challenging and it will impress everyone–especially you! I have discovered the following tricks over the last eight years while building a successful glass block installation company in Palm Coast, Florida. You will not find them on any installation guide out there, because installers don’t write the guides!

Start with the fun stuff–design the window. There are only a few manufacturers of glass block–Pittsburgh Corning (distributed by Home Depot and Lowe’s, to name a few), Weck, and Mulia. Personally I prefer Mulia–the price point is usually lower, the block meets the same design standards (all 4 inch deep block meets the Florida hurricane codes–the toughest standards in the country), and Mulia paints the interior edge of the block, which makes a nicer detail when the window is finished. All three make similar sizes and patterns. Design with the opening in mind–Pittsburgh Corning has a great guide on their website for planning out the project. Whichever block you choose, you can use this site for a planning tool. Just be sure and plan for a masonry installation–it is the most cost effective, easiest to finish, and best looking. Follow that guide for a materials list: glass block, spacers, glass block mortar, panel anchors, reinforcing, and expansion joint. Don’t use channels; they complicate the project with no added benefit and less visual appeal.

Tip #1–The rough opening size

You want the rough opening to be one inch over the nominal dimension of the window. Simply put, if you want a window six blocks wide by six blocks high, using eight inch block (the standard size) your nominal dimension will be 6 block x 8 inches = 48 inches + 1 inch = 49 inches. Now that you know the standard, know the tolerance. The actual size of the glass block window will only be 47 3/4 inches x 47 3/4 inches. That 49 inch opening you are shooting for can vary up to an inch, and you can still make the window fit. So don’t split hairs.

Tip #2–The bed joint

The bed joint is the foundation–it is a layer of mortar set on the window sill. If you have a true one inch over the nominal size,split it and make a half inch bed joint. You can guesstimate this, just check the opening after the bed joint is down to insure that you have enough room for the glass block. The secret to a window that lays itself is the bed joint. Put down the mortar (made the consistency of home made mashed potatoes), then dust it liberally with dry mortar. This will allow you to level this bed without the level sticking to it. If you start with a firm, level bed, you will seldom have to make any adjustments as you go up. Using your level, create a flat bed roughly 4 inches deep, to accommodate the depth of the block. Taking your time at this step will save you time and aggravation the rest of the project!

Tip #3–The butter!

Spreading mortar on the edge of the glass block is affectionately known as “buttering the block”. Butter the first row as follows: The left side and right side of the block, butter to fill the void to about 1/4″ beyond the lip. This leaves enough mortar to adhere to the next block. Most importantly, butter the bottom of the block flush to the outside lips. It is very important that this mortar remains flat, as this will bond to the bed joint and insures that the first course is as level as the bed joint. If your butter is lumpy on the bottom, you will have to work harder to level this course. Work smarter, not harder! This is the only course that will require butter on the bottom of the block. Throughout the rest of the window you will only butter the sides, except for the last course, which will be buttered on top as well.

Tip # 4–The level that acts like a straight edge

While a four foot level is used to keep the block level, keep a six foot level on hand to keep the block flush to the outside of the opening. This eliminates the need to worry about whether or not the glass block is tipping in or out. Simply hold the long level so it bridges the opening, then tap the glass block to the level. Do this at the top and the bottom of the glass block, to make sure that you are plumb with the wall.

Tip #5–A good grout job can make a good window look great!

Conversely, a sloppy grout job can ruin a great window. Once you have snapped off all of the spacers, take a minute and sponge down the whole window. Doing a preliminary cleaning at this stage makes your final cleanup much easier. Scrub any tough spots, paying close attention to the corners of the block, where mortar likes to build up. Using a textured grout float, spread the mortar just like tile grout, filling all joints flush to the block. The wipe down is the key to grouting. Start by wiping down the whole window, focusing on smoothing and flattening the joints. Next wipe three blocks at a time–any more will just streak the mortar. Wipe three, flip the sponge, wipe three, rinse the sponge. Think of the sponge like toilet paper, and never wipe twice with one side! If you have some streaks left, don’t worry about them, they will dust off with a towel after the grout has dried.

Tip #6–Kudos

Invite your friends and/or family over to show them how handy you are. You just became the expert!

Bonus tip–Protect your hands!

Mortar in general and glass block mortar in particular is very hard on your skin. There are many gloves on the market, but my favorite are disposable powdered latex medical gloves, found at any drugstore in boxes of 50. Change them occasionally, as they will get small holes in them, but they protect your skin while allowing you to feel what you are doing.