Glass polishing scratch repair 'How To' - Alfa Romeo Forum
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(Post Link) post #1 of 4 Old 03-06-13 Thread Starter
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Glass polishing scratch repair 'How To'

Greetings Alfisti’s.

I have been reading so many useful threads to assist me with my gtv restoration project in all the areas, some quite daunting for me to tackle. I think the time has come for me to give back a little of my personal expertise.

Firstly a bit of my credentials: My business of a handful of employees in Australia is to service glass. One of the contracts we have is with a prestige car company in Adelaide [which own the rights to sell Audi, Bently, Aston Martin, Volvo, Landrover etc blah blah] is saving glass on vehicles from having to be replaced. [you would be surprised how many of scratches are on brand new cars caused by techs, detailers and tinters using scrapers to remove stickers etc]

So this thread is a ‘DIY How to’ for scratches to glass [this only works on alfas…lol].

I personally have quite an involved tool box I take with me on site but I endeavoured to create this ‘how to’ with almost only hardware products.

What you need:
Image1
A scratch:
I have a picture here of a wiper arc scratch from a neglected wiper that has scratched a semi circle in the windscreen. It’s quite substantial and you can feel it with your nail.
Image 2
The DIY kit:
1. Spray bottle with water
[Preferably demineralised or pure Reverse osmosis water but not essential on a small job].
2. Small sanding kit with arbour for drill attachment.
This was a rust removal sanding kit from hardware should be pretty cheap anywhere.
3. Compacted felt polishing disc.
The one I bought had the same plastic screw attachment for the backing disc but you could glue a felt pad to one of the spare sanding discs if it doesn’t have an attachment.
4. Heat resistant foam about 4-7 mm thick.
My hardware didn’t have this but some do. A rubber and foam co will of course but foam without heat resistant qualities is not essential on a small job as I use this film on vandalised shop fronts and some foams melt at high temp.
5. Variable speed drill roughly 3-5000 rpm.
6. Lint free cloths and masking tape [to mask off duco if the scratch is close].
7. Scissors and nail brush
8. Cerium oxide [lapsa] this is the only product that wont be at most hardware stores but I have provided a link to easily get it on ebay cheaply [about 5pounds]. If you search cerium oxide a variety of polishes will come up. The one you want will be peach or pinky brown in colour [also known as lapsa]. You only need a couple of pinches for each job so it will last a DIYer probably the rest of your life.
http://www.ebay.co.uk/sch/i.html?_tr...at=0&_from=R40
9. Wet and dry sand paper. In the picture I have 1000 and 1200 grit but I also used 600 as the scratch in my windscreen was deeper than first thought.
10. Small bottle of quick dry super glue. [I use Selleys]
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(Post Link) post #2 of 4 Old 03-06-13 Thread Starter
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Preparation:
1: Using the super glue. Adhere the backing discs to the foam. In the picture I did 2 but I used 3.
2. Cut the foam into circles leaving a couple of mm around the edge.
3. Super glue them to the back of the 3 grades of wet and dry. So you know have a sanding disc with 600, 1000 an 1200 grit.[stick a piece of tape on the back and write the grade of grit on each as they will all appear the same]
4. To prepare the polishing felt disc [btw be mindful of not getting any contaminants on this disc as it can cause swirling scratches if it has some dirt or such on it, so keep it in a small plastic bag ] spray it with water then push a few pinches of cerium oxide evenly spread on the disc.
5. With water only clean the glass where the scratch is and the surrounding area of contaminants and car wax. Buff it dry with a lint free cloth as the sanding is done dry and the discs will skid if it’s wet.
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Sanding off/out the scratch:
When sanding a scratch out you will start coarse and get finer with each stage [this is called lapping]. The depth of the scratch will decide which grade grit you will start with [it will take a bit of experience to choose by eye].
With the example in my photos I started with 600grit.
When you sand glass you need to hold the disc slightly off perpendicular so that the scratches your disc make are like semi-circles or crescents.
Do not hold the disc at a too sharper angle or you will remove too much glass and get a repair job that looks distorted.
Try to let the sandpaper grip the glass and sand rather than slide. Continue until the initial scratch is gone.
While you do this keep 2 things in mind:
1: temperature of glass.
Check the temperature with the back of your knuckles [oils in your skin cause the disc to skip if you touch with tips of fingers and you want to keep it porus].
It should be hot but if it’s too hot to touch let it cool for 5min and then resume or simply sand another area if the scratch is long [if it gets too hot for too long it could crack].
2. Secondly at 20-30 second intervals stop sanding and give the disc a bit of a clean with the nail brush [leave some whiteness as it helps with grip when sanding].
Don’t do this while spinning as the plastic will go onto the disc and cause it to skip and you will loose the nice grip the sanding should have.

After the first sanding stage use the next or finer disc and re-sand making sure the crescent shaped sanded areas are gone.
If by eye you can’t tell the difference between say a 600 scratch and a 1000 scratch sand them in different directions that way you will know if you have gotten rid of the scratches from the previous stage thoroughly.

When you have finished the 1200 grit stage and you are happy that there are only 1200 grit scratches in the glass you are ready to polish.

If during any of the sanding stages you feel the ‘wet and dry’ has been worn too smooth and is not sanding, do not try to remove the old sand paper. Glue a new one over the top.
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Polishing:
Attach the felt polishing disc.
Wipe the glass with a clean dry cloth of any white glass particles.
Spray again the felt disc once and also spray a couple of pumps of water on the sanded area.
Hold the disc flat to the glass and polish the area until dry.
You know its polishing well when the disc is gripping the glass causing more friction and thus polishing faster. Again check the temperature with the back of your hand regularly as more friction also means more heat.
Spray the area with water and wipe it clean with a second cloth and see how the polishing is going.
If it still has grey porus areas spray with water and repeat the polishing and checking process until you are 100% satisfied with the repair.

I hope this helps with keeping your Alfa up to scratch [bad pun, sigh].

Btw it takes me quite a while to train people to polish glass depending on their personal ability to pick up a new skill so be smart and practice on an old piece of glass before destroying your windscreen.

Tip: if you’re not brave enough to sand your car glass the polish used also gets off water stains, calcification and oxidisation without the need to sand.
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File Type: jpg 20130602_113442.jpg (53.4 KB, 24 views)
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