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MATERIALS : Glass Blocks: Clearly Versatile

November 19, 1994|From Associated Press

Glass-block walls, windows and other design features are being installed in more homes for reasons besides pure stylishness.

Easy care and reasonable cost stand out; but, perhaps more exciting, no other material so successfully transmits light while maintaining privacy, enhancing security and providing both thermal and acoustical insulation.

Building a simple glass-block partition wall or room divider is a good beginner's project. Except for certain kits, all glass-block installations require modest carpentry and bricklaying skills.

Block walls generally must be framed for support by a sturdy wooden beam, or header, across the top, a wood or concrete sill at the bottom and one or two vertical jambs along the sides. Consult the block manufacturer for details. Before attempting a large project, show your design to a building inspector.

Glass blocks come in two thicknesses--3 1/8-inch and 3 7/8-inch and several square, rectangular and other sizes with sides ranging from six to 12 inches in length.

Mortar is used to bond most blocks (some kits use acrylic strips and silicone sealant instead). Plastic spacers are set in the mortar joints to maintain uniform gaps between blocks, and special metal is used to secure the blocks to the framework.


To build a partition wall, start by joining the sill, jamb or jambs, and header to create the supporting framework. Next, arrange the first row, or course, of blocks and spacers on the sill without mortar to test the fit.

Using the course and the intended width of the mortar joint above it as a guide, mark the heights of the subsequent courses on the jambs.

To eliminate extra space, plan to install wooden filler strips against the inside of the framework. Then remove the blocks, brush the sill with a coat of asphalt emulsion sealer to protect it from the mortar and let it dry for at least two hours.

As a final preparation step, loosely tack fiberglass expansion strips (sold with block supplies) to the jambs and the header.

Spread a smooth bed of mortar onto the sill and install the first block at the corner using spacers between it and the jamb.

Mortar for glass block usually is mixed to a drier consistency than brick mortar and is colored white rather than gray, for better appearance. Tap the block into place with a rubber mallet, then fit spacers against it for the next block.

Apply mortar to the adjoining side of the next block and repeat the previous steps. Continue to the end of the first course; then check that the entire row of blocks is level and that all blocks are aligned.

Spread mortar on top of the first course and install the second course the same way. After the second course, embed a right-angled metal panel anchor in the mortar at each end of the wall. Slit and lift the expansion strips and fasten the anchors to the jambs; then re-secure the strips over the anchor.

Attaching and Installing Anchors

Install anchors on top of every other course. After the next to last course, attach anchors to the header so they will extend vertically between every other block in the final course.

Remove visible parts of spacers and smooth the mortar between blocks as soon as pressing it gently leaves a thumb print.

Slide a bricklayer's striking tool along each joint, working from the bottom up. Promptly wipe cement haze with cloth and a dry, non-metallic abrasive pad. To finish the project, fill the gaps between the blocks and framework with caulking compound.

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