How to Replace a Broken Window Pane With Plexiglass

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Plate glass is breakable, and when it shatters, it creates a hazard both in the window where it was once installed and on the ground underneath it. If a stray baseball has put you in the situation of considering alternatives to plate glass, you might consider tempered or laminated glass, which are still breakable but not as hazardous because they are shatterproof. But there's an even safer alternative you might not have considered.

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Acrylic plexiglass sheets are 17 times stronger than glass. They are also cheaper and more transparent, according to industry literature. Crucially for a homeowner with a broken window that needs immediate repair, plexiglass is easier to cut and handle, and it's safer. It makes a lot of sense to replace that broken window pane with plexiglass, and the procedure isn't difficult.

How to Cut Plexiglass

Unlike tempered or laminated glass, you don't need to have plexiglass precut at the factory. You can cut it yourself with a circular saw or table saw. To get the best results, choose a metal and plastic cutting blade. Leave the protective coating on the plexiglass, mark the cut line on it, and cut carefully along the line. The rough edges shouldn't be a problem after the plexiglass has been mounted in the window, but if you want to smooth them, you can do it with sandpaper.

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If the plexiglass is thinner than 3/16 inch, you can also cut it with a utility knife. Just score a series of lines along your cut line, turn over the sheet and do the same on the other side, and then place the sheet on the edge of a work bench and snap along the score line.

Remove the Broken Glass Carefully

Once you've cut the plexiglass to the dimensions you need, put on a pair of gloves and some goggles and prepare the window by removing the broken glass. Start by picking up all the glass on the floor around the window and put it in paper (not plastic) for disposal. Then remove all loose shards of glass from the window and put them in the bag.

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Use pliers to grip and remove shards that are stuck. Some won't come out until you scrape off all the old window putty, which you can do with a flat-head screwdriver or stiff putty knife. If the window has plastic or wood stops, pry them out with a screwdriver. Once all the putty and stops are gone, use pliers to pull out any glazing points, which are small, triangular pieces of metal embedded into the frame to hold the glass.

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Install the Plexiglass

You install plexiglass in a window frame in pretty much the same way you install glass. Shoot a bead of clear silicone caulk onto the frame for weather sealing and then pull the protective coating off the plexiglass and fit it into the opening. Tap a few glazing points into the frame to hold it in place and wait a few hours for the caulk to set.

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Once the caulk is firmly holding the plexiglass in place, you can coat the outside perimeter with glazing putty or paintable caulk. If you pulled wooden stops off the old window and they're still usable, you can use those to hide the edges of the new window. If you do this, the glazing points will be in the way, so pull them out before nailing the stops to the window frame with 1-inch brads or finishing nails. You'll still need to apply a bead of paintable caulk between the stops and the window to keep out the cold air.

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