Sunday, March 11, 2012

Using Mylar to make mirror

Mylar glued to aluminium using contact adhesive -
Very Very Wrinkly!! (but still reflective)
11 March 2012: I bought some Mylar by mail order, 1.5m x 5.0m on a roll. The idea is to try and see if the mirror function will work better now that the aluminium is so tarnished. Mylar reflects about 98% of radiant heat energy falling on it. It is used in horticulture for increasing light falling onto shaded plants, and I note that it is used for indoor cannabis growing, something I don't intend to do!

The Mylar is not mirror finish, but it is very bright, like very clean Bacofoil, and being plastic, it doesn't crumple like Bacofoil. It is double sided, and very slightly transparent.
Mylar, highly reflective, but inexpensive
  I wondered how to fix it, and it turns out my son is also thinking of how to get a mylar-type finish on a larger item that he is building, a full size flight simulator. He has access to industrial methods, but I only have my bench in the garden.
   My idea was to tape it on with exterior quality duct tape, but we thought I could experiment with contact adhesive, using the mirror that is over the kitchen window.
   Here is the first result, using adhesive. It looked fine when I first did it, but after 18 hours, the surface has resolved into a complex pattern of wrinkles. The mylar has glued well, but any air trapped could not escape, and small air bubbles grouped together. It is very brightly reflective, but energy is scattered, and I don't know how it will weather. A smoother finish is required.
The aluminium reflectors look bright in this
photo, but it is relative - they are very
tarnished. Mylar would change them
dramatically!

Fastening to upper mirrors
If I had an 'industrial' method such as a power roller, I could roll out the small wrinkles, if working on a flat bench with sprayed contact adhesive. The mirrors on the Sunbox are not detachable easily (without a scaffold) and for quick attachment without adhesive, at high altitude, the tape seems to be the only method. I don't go up the ladder very often, but get slight herby-jeebies every time, wondering if it is my last time!
  Taping would be more easy to stretch to get a more optical finish and smoothness, and it would be replaceable every few years, as tape can be replaced and Mylar is very cheap. The carriage cost as much as the roll!

The interior mirrors also need some Mylar, and as these are not exposed to wind or weather, they would probably be easy to tape, and very long lasting. At the moment, there is some aluminium sheeting in there.

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