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Glass Blocks Tips and Tricks, continued

Wall Ties, Reinforcement, and Expansion Joints

Lateral support and joint reinforcement are required by the UBC (sections 2110.3 and 3110.4), spaced no more than 16 inches on-center. If you are in a seismically active area, check local requirements. Lateral support typically consists of wall ties (also called panel anchors), which are galvanized metal strips that you embed in the mortar joint and nail to the wall with galvanized nails (Figure 8).


Figure 8. Every other course gets a panel anchor nailed to the wall with galvanized nails and embedded in the mortar.

Reinforcement uses a galvanized wire ladder-bar, like the type that block masons use. Bear in mind that the reinforcement takes up space in the joint, so you will have to arrange your spacers accordingly. Expansion joints are flexible strips that replace the mortar at the top (head joint) and at the outer vertical edges (jambs) of the block installation. This material prevents structural loading of the block by accommodating normal movement from expansion and contraction, and is required by the UBC (section 2110.6) and the manufacturer. You can usually buy all of these accessories from your block distributor.

Raking the Joints

One of the things that catches people's attention about my glass block installations is that the joints are clean, crisp, and symmetrical. Here's how to do it. After you have set a course, rake the mortar joints about 1/4 inch deep, using one of your wood spacers. Do not use a metal tool, because you risk scratching or chipping a block. After all of the block is installed, you'll come back and grout the joints with sanded grout, just like you'd do with tile (Figure 9).


Figure 9. Sanded grout is applied evenly to the raked-out mortar joints.

Grouting the joints. There is no way you'll get the mortar to finish out as evenly as grout, so don't bother trying. Besides, with this method, if the mortar does crack, it's irrelevant since the grout will hide the cracks. If you can grout tile, you can grout glass block; there's no difference. Apply the grout with a rubber float, work it in well, let it set up, and wipe it down with a grout sponge (Figure 10). Keep the sponge clean and a bucket of clean water handy (this is the point in the job where it's nice to have a helper).


Figure 10. The author carefully wipes down the grout to get a dense, even finish. The haze is sponged off, leaving clean joint lines (inset).

You'll see a haze develop on the block after you wipe it down the first time. At that point, you wipe it down again. You aren't just cleaning the block off, you are also floating the grout lines. This is what produces that clean, crisp appearance. It takes some practice, but it's not difficult. If you float the grout properly, you will get a dense, even finish. Don't worry about abrading the glass block, it's plenty hard enough.


This last phase of the job is essential. Go back over the block one more time with the sponge, making sure there is no grout film on it. Remove all of your masking and leave your work so clean that nobody else has to touch it. The sparkle and symmetry of a beautiful job should be the only thing anyone sees when they look at the finished wall.

Ron Porteris a contractor from Pecos, N.M., who specializes in high-end glass block installation.