Clean windows

If these are acrylic, or any other polymer - I would not use a metallic scraper.

Find an old piece of acrylic and grind the edge to about a 45 degree angle. Grind the edge using a fine grading wheel. so that it is sharp. It should finish looking like an old fashioned plane blade. Use it as a scraper. If you have lots of windows the acrylic will need sharpening occasionally and making the 'non working' end into a handle will make it easier for your wife to do it. The 'blade' needs to be straight and if you are careful in how you make it - it will go into corners. A sophisticated tool like this is excellent to remove silicone etc. and will last your wife a lifetime. :)

You may need to soften the adhesive with solvent, diesel might work as also might turps, acetone or meths - your guess will be better than mine.

Jonathan
 
Try citrus cleaner.
If the windows are polycarbonate, then stay away from solvents. I once ruined a brand new polycarbonate window, when I tried to remove excess sealant with acetone.
Acrylic plastic windows is softer, but can be washed with solvents. If you get scrape marks when removing the glue, you can remove them like you would remove scrape marks on gelcoat. You can rub it and buff it.
 
There is a useful solvent called 'Goo Gone' I think it is a petroleum/ lemon concoction, made in the U.S., don't know if it generally in NZ but worth a try.
 
If these are acrylic, or any other polymer - I would not use a metallic scraper.

Find an old piece of acrylic and grind the edge to about a 45 degree angle. Grind the edge using a fine grading wheel. so that it is sharp. It should finish looking like an old fashioned plane blade. Use it as a scraper. If you have lots of windows the acrylic will need sharpening occasionally and making the 'non working' end into a handle will make it easier for your wife to do it. The 'blade' needs to be straight and if you are careful in how you make it - it will go into corners. A sophisticated tool like this is excellent to remove silicone etc. and will last your wife a lifetime. :)

You may need to soften the adhesive with solvent, diesel might work as also might turps, acetone or meths - your guess will be better than mine.

Jonathan

Acetone will quickly melt acrylic.
 
Be careful with any solvents if the windows are not glass. Also alcohol, especially propanol, can be very bad to acrylic.
People have ruined their portlights and hatches with alcohol-based cleaners withour ever knowing it, since the internal cracking/crazing in the acrylic starts after some time (can be weeks) and the cause remains a mystery.
 
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