Glass block windows provide extra security

February 14, 2009|By PAT LOGAN / Creators Syndicate

Dear Pat: Some of the windows where I live are sheltered by shrubs, such as those in the utility room, making them good targets for thieves. I want to install glass block windows. Which is the best type to install, the standard mortar type or those from a kit? - Jean M.

Dear Jean: Glass block windows do provide more security than standard double-pane windows. Even if a would-be thief breaks through one or two of the small sections and reaches in, glass block windows do not open. It would take quite a while and make a lot of noise to break through enough of the mortar grids to actually enter through the window.

For strength, installing individual glass blocks in mortar is the best method. An experienced installer can do this quickly, so hiring a professional might be your best option for windows that are visible from indoors.

For a utility room, a perfect, neat, indoor appearance is not as important, so you might try to do it yourself. Even if the finished job does not look perfect, it will still stop a thief from breaking into the window. It will also seal out air and water leaks


The first step to installing individual glass blocks in mortar is to select the type of glass blocks. For a utility room, a clear view outdoors is not important. Instead, select glass blocks with a medium surface pattern to provide privacy from outdoors, yet allow diffused natural light to pass through.

Once you have the old utility-room window removed and the opening cleaned out, it should take about a half-day to install a glass block window using the mortar method. If you start having problems after installing a course or two of glass blocks, you can stop there and seek assistance.

Determine how many and what size glass blocks you need to fill the window opening. Blocks are available in several sizes so you will likely need a variety of sizes to properly fill the opening. The optimum gap between the glass blocks for the mortar joints is one-quarter to three-eighths of an inch.

The next step is to prepare the sill for the mortar and the first course of glass blocks. Coat the sill with a water-based asphalt emulsion to seal it and let it dry for a couple of hours. Nail a polyethylene expansion strip to the header and window side jambs.

Lay the proper thickness of a mortar bed on top of the dried asphalt emulsion. Place the base course, or horizontal layer, of glass blocks on this mortar bed, leaving the proper gap between each glass block. Using a rubber hammer or the handle of the trowel, tap the blocks down into the mortar bed. Fill the vertical gaps between blocks with mortar.

Spread another layer of mortar over the first course of blocks and place the second course on top of this layer. Tap them in place. It would be wise to install steel reinforcing rods between every second course of blocks. Spread only a half thickness of mortar, place the rods and spread the rest of the mortar so the rods are totally surrounded by mortar.

Before the mortar gets too hard, smooth the mortar joints for a nice appearance. Clean out a gap around the perimeter and fill it with packing material. Finish the perimeter with wood or aluminum trim.

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