What happens at the surface of any type of glazing will always be different from what you might expect. This is because surfaces are always chemically different from the chemical identity of the whole. Another way of putting this is that the interface between a solid and the air or liquid that surrounds it will always have its own chemical identity. This is important to us because we are always working with surfaces. Let me site a very interesting and to me totally fascinating example.
Take acrylic glazing. Or Plexiglass. Polymethylmethacrylate. The next time you are standing underneath an acrylic dome skylight with the sun shining brightly directly through it;…look up. If it has any age you will see many small cracks that will appear as bright dots or small cracks. That is exactly what they are. Small cracks. They are caused by uv light from the sun. It happens at the surface. The uv has just the right amount of energy per wave to cause the molecules to move. When they move they line up with one another. This creates microscopic spaces. At the surface. In time with more uv and stress from sound and vibration such spaces grow into microfissures. Yet these are still too small to be seen. As more time passes the microfissures get bigger until visible stress cracks form. Which also will become bigger in time and increase in number. In this case it is radiation that initiates the damage. However it is also possible for chemicals, in particular organic solvents to cause the same kind of damage. Especially when also coupled with physical stress. Take a look at this.
Take a small one by one foot piece of plexi. Put a thin piece of paper towel down the middle about one inch in width. Wet it first with some alcohol. Methanol or isopropanol should work well. Then bend it over your knee at about a thirty degree angle. It should break completely in half in about thirty seconds. Makes for a fantastic demonstration if you are trying to land a plastic dome skylight job. Or anything plastic! You can test different organic solvents and other products (made just for plastic glazing) using this test. Some solvents will leave many small cracks but will not break the sheet in half. Some will only leave a few. The bottom line here is that most solvents will do no harm unless the plastic/window is stressed in some way. Even over time. So if you leave even a small residue behind it might not cause cracks until a month later. It is always best to test whatever product or chemical you want to use on plexi before you do it. What is even more interesting about this test is that it has allowed me to find certain chems that will dissolve different paints while doing no harm to plexi. Then to add them to superabrasives such as aluminum oxides used for removing scratches from plexi to remove paint from plexi without doing any harm at all to the plexi.
Polycarbonate is chemically different from plexi. It is polycarbonate and goes by different names such as Lexan. It is more likely to haze (discolor/turn a cloudy white) rather than to craze (crack up). The test for this is to take a one by one foot piece of Lexan/polycarbonate. Heat it in your oven to about a hundred degrees to simulate the hot sun. Remove it. Apply the chem/product in question all over the surface. Then put it under some warm or cold tap water. This is what you would do if you were working on a dome skylight in the field. Guys that have hazed polycarb skys tell me nothing happened until I put my soapy water based cleaner to it. To remove the plexi product. Then it hazed over. What did I do wrong? I used the companies product that was sold just for this purpose. It is a professional product! So I went to my tinkering room with a brand new sheet of Lexan at top dollar and duplicated the results they got. Couldn’t restore the haze. Called back and said, sorry man you are deep in doo. Simply stated never work on plastic glazing with anything until you do the test first. Cuz you might not know, but the SURFACE will.
When someone just wants to clean plexiglass, what chemicals would you recommend first trying? Also, if there is already a haze should I just recommend the customer get new plexiglass? One more: What would you do for scratches?
To clean I have always just used dishsoap and water with a soft applicator and a small squeegee if curved in three dimensions. If my memory is good you will find that the organic solvents with high evaporation rates will do the most damage to acrylic surfaces under stress. And again, acrylic/plexiglass will crack up whereas polycarbonate/Lexan will turn a milky white haze. Temperature is enough to damage polycarb when the chem is right. I discovered that the organic solvents with a slower evaporation rate were the least effective at dissolving paint, etc. There are some powerful alkalies out there however that will eat up paint but will not craze plexi. Again if my memory is OK a 50/50 saturated sodium carbonate with water will eat up inferior epoxies but won’t craze plexi. Do the test.
For scratches there was a product called Novus years ago that worked well. It was a compound. Many are out there today. They are based on aluminum oxide. I will be developing several compounds for taking scratches out of plastic glazing. As I move more into product development I will be specializing in compounds. When looking for products that work well I have always tested them on brand new glazing surfaces. If you want to find products for plexi go to a plexiglass display case manufacturing plant. Or just call them. Also. There used to be a product called Brillianize. Mostly water. It did an incredible job at shining plexi. Created a super slippery surface also.
For example. A barrel vault plexi skylight is curved in three dimensions. Or at least the two ends are. You can use a long squeegee on a two dimensionally curved window or skylight. Flat windows I guess would be one dimensional.
I don’t know if I’m asking this right but how can you tell if a “plastic glazing” is polycarbonate or acrylic if it isn’t damaged by scratches or hazing.
One more: If you see haze, can that ever come off?
Your first question is a VERY good one. I suspect there must be a very simple way to tell the difference. But I just don’t know right now. I would guess it should be possible to do a very small spot test with a chemical known to haze polycarbonate on contact but never acrylic.
Second question. It should be possible. But would be a lot of work. Depending on how thick the haze was. Whereas it certainly would not be possible to remove cracks from acrylic. They would go much deeper.
I was looking for different products for cleaning and found that the EPA won’t allow water spraying on the tarmacs at airports so the people cleaning the planes use this product. They get it in five gallon drums and it gets applied with rags, it dries in 30-60 seconds and gets wiped off. I guess its a glorified version of the dry wash car wash product. I heard about it from a guy that detailed cars. He mentioned that it had Teflon in it - I have no idea what that means. I’m not so sure I found the exact same product he was talking about or another version w/out the Teflon since mine came in plastic gallon jugs.
I use it to clean things like a high up and away metal louver that wasn’t touched for years that had dust and cobwebs. Because there was new paint on the walls and carpet below I didn’t want to use soap and water. The DryWash cleaned it with no drips or run down.
Let me know if you learn anything on it or if you can recommend a product that can be applied to an entire building surface that could protect it from the elements. The DryWash would be hard to apply to a 40 story glass structure vs an invisible shield type of product. I have an application method that can be used easily if the product is a liquid type.
