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Glass Polishing by Machine - Defect Correction

35K views 28 replies 24 participants last post by  wyliss 
#1 · (Edited)
Search the forums and you will find thousands of threads about the correction of defects from paint - hard paint, soft paint, white paint, black paint, pink paint etc etc etc... But you'll also notice a complete dearth of threads about removing defects from glass! In this thread I am going to introduce a technique and polishes I have been using on glass in testing in recent months, with further threads to come with more detailed results as well.

First things first - glass is tough! Very tough! Think the hardest paint type, and multiple by "A Large Number" and you're getting there! Many glasses you can clean with steel wool and not scratch them! So, as you can probably imagine, the use of traditional paint polishes and abrasives is rather out of the question. But how then, can we deal with marks like this on glass?







These marks are wiper sweep marks, typical on a lot of glass. In particular, Porsche owners complain of their windscreens being afflicted by this wiper sweep marking which can be very distracting on a sunny day!

Removal of such marks requires specialist abrasives designed for task - cerium oxide is one such abrasive type, and is found in a few glass correction products. The one used for these tests is Liquid Glass, produced by Rapid Autocare. It is supplied in a kit designed for use with a drill - comes with the polish (very watery) and a couple of rayon pads. A a sponge which I am sure has a use, but not sure what it is yet - was useful for blowing my nose though.

Now, one major concern here is heat. The correction of glass requires a lot of effort owing to its hardness and this can lead to large heat build up. It is important to monitor this very carefully, as high heat can disform the glass, distorting vision and making a replacement necessary. Always be aware of this when glass polishing! Using a drill, if you stay in the same place too long, you will distort the glass - trust me ;)

The techniques that we have been working on for glass involve the use of a rotary polisher, a 2" backing plate (Ben at Carnaubawax Shop has them :)), and 2" Rayon pads (again, Ben has these, or use the ones in the kit). The pad is primed with the watery polish, and a region of about 6" square at a time is polished as follows:

  • Spread at 600rpm
  • Begin to work at 1200rpm, light pressure and maintain this speed until polish well spread to avoid splatter later
  • Work at 2000rpm, light to medium pressure, slow machine movements for a minute or so
  • Work at 2500rpm, medium to heavy rotary pressure*, slow machine movements monitoring the heat very carefully until polish starts to dry a little
  • Finish at 1200 - 1500rpm, light pressure and faster machine movements

* Be very careful not to bow, or break glass with too heavy pressure and at all times monitor the heat. It should never get too hot to tap by hand, perhaps a little too hot to hold for a while.

Essentially a high-speed Zenith Point technique, with a typical set lasting three or four minutes. Care was taken throughout to monitor the heat of the glass (did I mention heat again? Its important ;)). The results, here on Vauxhall Astra glass, are as follows:







A definite difference, and a definite improvement! These results have been replicated during details too thus far, most notably on a Porsche 911 which Gordon detailed recently :)

Further testing is still required for dealing with deeper glass scratches, and further writeups will follow based on this and alterations of the above technique. Hopefully this will give a flavour for what is possible on glass though with a rotary polisher and the right products :)

I would like to thank Gordon (caledonia) and Davy (badly_dubbed) for their help in this test :) ... We three are the lab monkeys!! :D
 
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#5 ·
This was a heated rear screen that it was used on in this example here.

Triplex glass, the one with laminate inside as you describe, is susceptable to heat - I know this through testing :) However, it was not discolouration, but rather distortion of the glass, perhaps the laminate getting too hot and distorting. But in all cases, you would want to be very carefully monitoring the heat build ups and minimising them where possible. While this glass correction is possible and can be achieved, it should be viewed IMO a bit like wet sanding - its a last resort option, required only if you cannot sleep at night because the glass scratches are so bad! The possibilities for issues are there and should always be considered, and a new pane of glass would be needed in the event of discolouring or distorting.
 
#9 ·
Hi Dave.

Great write up. The reason we include the Sponge is so you can clean the glass and check progress. This is needed when customers use the retail Kit as the drill is more difficult to control than a rotary and you can actually create quite a lot of mess.

Also in the instructions we advise that if any of the Glass Polish should get on the paint, to use the sponge fully wet with water to lift off the polish due to it's high level of abrasiveness:thumb:
 
#12 ·
Personally on a windscreen I wouldn't try polishing defects out. Its just not worth it - one tap with a sharp instrument and a quick phone call to Autoglass and you can have a brand new screen for 50 quid on your Insurance.

Rather that the worry of getting distorted field of vision from over zealous polishing - Not aimed at you DAVEKG - just alot of amateur polishing can ruin a screen easily.
 
#13 ·
Take you point on board however we have saved many screens that would have failed MOT's which would have required a new screen at substantial cost to the user.

So for around £17.00 it provides a very cost effective solution. Regarding users we have sold nearly 5000 of these kits since launch into the retail sector and have yet to have an issue with anyone damaging screens.

I would also expect the members on here to be more capable than most high street consumers so fear not regarding screen damage.

It would take some considerable time to polish the screen and warp the glass with the standard kit. We do urge caution on the instructions to be on the safe side:thumb:
 
#19 ·
Having worked for 2 of the major aoutmotive glass replacement companys in my time, i find this interesting.
Toughend glass is so fragile. As Bigpikle says, it basically tensioned glass. Ive had heated rears blow up with the slightest touch to them. Also seen them dropped by accident and stay complete. Little or no heat, in my opinion is the only way to go with polishing toughend glass.
Laminated glass is different story. All modern front screens and some rear heated screens are in laminate. Some older vehicles may still have toughend. More heat can be usd to polish, but be carefull as too much heat in 1 area can cause delamination. Basically where the the plastic laminate layer betwen the 2 layers of glass starts to bubble.
As with all industries, glass technology has come a long way and polishing by Dave is looking good.
Something you should consider is the quality of the glass. That may sound silly, but not all glass is the same. A certain replacment company, in orange vans, have there own manufacturing facilities. To be honest some of the screens that came out of there was shocking, warped screens were a common occurance. The screens just felt of an inferior quality.
The other major company in white vans on the other hand have much better pedigree. There group company actually owns or has part shares in most of the glass manufacture. So the glass they fit is mainly OEM. At least you know, most of the time, you are getting factory standard replacement.

Steve
 
#25 ·
Excellent stuff Dave, thanks for taking the time and effort yet again to educate us mere mortals.

Out of curiosity and im probally being stupid but do you think using the raw materials that make glass would be of any use for revitalising it. Limestone, Sand, Soda ash and whatever else is used.
Not exactly off the shelf stuff....lol
 
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