Through a glass diffusely

My workshop is a four car garage with two articulated doors, one at each end. This flexible space was one of the selling points of the house; I love being able to open a door in the front of back or both, depending on privacy or ventilation requirements.

These garage doors are new. When I bought the house I had the garage finished, also adding an upper attic level for storage, a skylight, diagonal seismic bracing, sheetrock, plenty of outlets and ethernet runs. I’m in love with the space now, and recently had a closet built around the HVAC, water heater and 19″ rack to contain noise. I also put in a thermostat sub-zone.

The two garage doors combined have twelve small windows. At different times of day hot spots of sunlight rove across the floor, so I have been thinking about some kind of diffusion. Also, eight of the windows are in an optically important location directly over a TV. At night the windows look black, but during the day the sky beyond can be unpleasantly bright in contrast to a dark image on the TV.

I wanted what I put on the windows to be easy to take on and off so I wouldn’t be stuck if I wanted to see sky again. That ruled out window films. It also needed to be lightweight and stay secure when the garage doors are raised and become horizontal at the ceiling. Anything hanging freely, such as curtains or blinds, were right out.

Translucent white plastic was the obvious choice, but I got discouraged by prices. I couldn’t find any online custom plastic that didn’t feel expensive to me. Big sheets are obtainable and not too expensive but I’m not set up to make large precision cuts. Finally, I found a good deal on restaurant quantity HDPE cutting boards that were exactly the right size. Here they are waiting assembly:

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Polyethylene is amazing stuff. It is very tough – these are cutting boards, after all – but flexible and translucent.

Each windows has ten screws around it, and my plan was to have each sheet held in place by one magnet for each screw. I bought these magnets for 5 cents each from China:

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The magnets made assembly unexpectedly cool. I unscrewed one window and used the plastic retainer to make one sheet into a precise master:

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Once I glued the magnets in place on one shade, I made the next 11 by placing each sheet over the master. Each magnet was affixed by putting a drop of super glue on the correct side and letting the magnet find the correct position by itself, just dropping it somewhere near the master’s magnet on the underside. It was very cool to see them slide into the correct position of their own accord, and the magnet even automatically applied pressure as the glue set too.

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Here you can see how the magnets line up with the screws:

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Those of you who have worked with polyethylene before are now laughing at me. Because – and I really didn’t think this through – one can’t glue to HDPE. There are special chemical/heat treatments that can sort of work to weld HDPE to the right plastics, but here I was just plopping some superglue on and expecting it to bond to the nickel surface of the magnets.

I discovered the problem after making a few shades and testing them. Sometimes the magnets would come off the HDPE and stay stuck to the screw heads instead of the plastic.

I would have liked to have some clever chemical solution to this, but I didn’t. Instead, I just made sure I glued to the less bumpy side of each sheet, and roughed the area up with sandpaper first. After doing this the success rate went from less than 90% to more than 99%, and enough magnets stayed on well enough that I stopped caring. I had to fix a few while testing, but no more magnets have fallen off since I put the shades up.

The completed shades from inside at night:

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From outside at night:

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From inside during the day:

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I’m happy with how they turned out. The light is nicely diffuse. I’m thinking now of attaching colored transparencies on the far side of each sheet to create a stained-glass effect.

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