Window glass on a classic car is not always an easily replaceable part. When you have scratches or chips in your classic car glass you may have only one solution which is in removing scratches from car glass as replacement may not be viable. Visibility in your vehicle is such a valuable aspect of its daily functional value. Scratched car glass not only impedes visibility but also predisposes your auto glass to other damage. All you need is a little ping from a road pebble to crack a structurally unsound windshield.
Any cracks or chips can lead to spider-webbing and the inevitable need for a complete replacement. I decided to put together a community resource for all auto owners to prolong the life of their vehicles. Please read below for an in-depth analysis of how to remove scratches from car glass quickly and safely.
Assessing the Damage Prior to Removing Scratches
There are a variety of reasons why your car glass is scratched up. Whether you were tailgating a truck hauling gravel, driving in an ice storm, misusing an orbital polisher, or simply drove through some low hanging trees, it is easy to imagine how glass can accumulate scratches from contact with anything at operating speeds.
The first part of the assessment is determining whether you have laminated or tempered glass. You simply must look on the lower corner of your driver’s side window to see if it says tempered or laminated. Even if the side windows are tempered, the front and rear windows are made of a more durable laminated glass.
This is an important distinction when it comes to repairing auto glass. All late-model vehicles produced after September 2017 were required by law to use laminated glass on all panels to prevent people from being thrown from their vehicles in accidents. The next part of the assessment is assessing whether the scratches are deep or shallow. Deep cracks require a considerable amount of care because any pressure you exert may be enough to shatter the windshield or crack it. This is because the surface tension of tempered safety glass is paramount to the retention of its integrity.
While you may be able to whack your side window clumsily with your elbow; if you use the same force with a small pointed instrument, the whole window will instantly shatter. Laminated glass has reinforced surface tension that requires much more force to shatter but still requires care when it comes to deep scratches.
The best manner of gauging the depth of your auto glass cracks is running your fingernails over the surface. If there is enough bite for your nails to catch, then you will need to a different kind of repair to prevent the scratch from cracking, spreading, spider-webbing, and failing.
You will also need the scratch-repair product itself, of which there are three options:
- clear acrylic nail polish – which many people have but only works on the shallowest scratches
- cerium oxide – which is the best product for most minor scratches, but few people have on hand
- baking soda and white toothpaste – which can work but often requires multiple applications
Clean the Scratch Prior to Removing Scratches
Before repairing the scratch, make sure there is no debris that will interfere with the bond between the repair product and glass. Thoroughly clean the scratched area with the glass cleaner and a soft cloth. There is no reason to clean the entire glass at this point, as you will get fingerprints and some product on the glass while repairing the scratch.
Mark the Scratched Area
As the repair progresses, it can become difficult to see where the glass was scratched. So, you always know where you should be working, mark the scratched area. The easiest way to do this is by outlining the scratch with a dry-erase marker on the opposite (undamaged) side of the glass. Alternatively, you can place a piece of tape on the opposite side.
Light Scratch Repair Process
Any repair process is going to require that you thoroughly wash and dry your windows to remove any contaminants that may cause further scratches. This will also allow the repair compound to penetrate without being repelled by grease or waxy residues.
Most of the products that are sold to repair light scratches are like rubbing and polishing compounds used to correct the finish of automotive paint. These products come in creams that you apply to a sponge fitting for an orbital polisher. Depending on the brand, you will simply apply the cream to the sponge and then use overlapping circular motions at various RPMs to polish out the fine scratches.
Even if you do not know how to remove scratches from car glass and this is your first time trying, this method is very straightforward and easy. The active ingredient in any quality cream is Cerium Oxide. Cerium Oxide penetrates the micropores of the scratches and bonds to the material to restore the surface and seal the repair.
3M makes a reliable product that is premixed and ready to apply. If you are doing the repair by hand, you will simply apply the 3M polishing compound to the damaged glass itself and use a cloth to work at it. Never apply too much pressure in any case because the Cerium Oxide should do all the work if you move it around.
Although the 3M product is nothing more than Cerium Oxide mixed with the ideal volume of water to form a paste, you may need to continue wetting the surface with a spray bottle. If an orbital tool runs too dry, it can overheat and crack the glass. Make sure the surface is lubricated and that you are letting the circular motion and compound do the work without trying to burn a hole in the windshield.
When the repair is finished, simply wash the auto glass clean and check the repair every so often to ensure that the area does not reform any scratches or cracks.
Deep Scratch Repair Process
When it comes to repairing those deep scratches that jeopardize the value of your vehicle, quality auto glass resins are the weapon of choice. If you fail to repair deep scratches, they can crack and force you to replace a windshield. Replacing windshields is problematic because cross-contamination of dissimilar metals can lead to rust cancer or white powder deterioration of aluminum.
Even if your vehicle is not made of dissimilar metals such as aluminum and steel, the risks of forming a leak are greater in a reinstalled windshield. These leaks can lead to electrical gremlins that can send any vehicle to the boneyard.
Resins come in a variety of viscosity ratings. A resin with a viscosity of 25 cps is like water. A resin that is rated at 1,600 cps is thick like honey.
Unfortunately, it is difficult for consumers to find the high-viscosity industrial grade auto glass repair resins. The low-viscosity resins that come in kits may be sufficient enough for a deep scratch but not good enough to retain the integrity of cracked glass. Therefore, it is better to have a professional repair deeper scratches if they’re isolated.
Typically, the resin is applied with a number of special tools such as injectors and vacuums to set the ideal volume of resin in the surface before hardening. A UV light is used to cure and harden the resin after the surface is sealed. When the repair is done correctly, you will not be able to tell that there was ever any damage at all.
Applying a commercial kit resin is little different than using nail polish or superglue. You must guesstimate the ideal volume of resin by applying it slowly and making sure to remove any air bubbles. Then use plastic sheets to firmly smooth out the surface.
You let it cure in the sun or under a UV light for 10-30 minutes and then scrape off the extra resin compound with the included razor blade. It is said to be an art form that takes some practice to get perfect results. Although these compounds are used for cracks, a deep scratch may be millimeters away from forming a crack so you should consult a professional if you are unsure.
Finally
Once the repair is fully made, wipe away any repair product that remains and clean the window. You can clean the entire window at this time. The result should be a clear glass without scratches in it.
For light scratches, the 3M Cerium Oxide compound buffed in with a rotary tool is probably about as easy as it gets. If your scratches are deep, you may have to weigh the consequences of doing it yourself against the convenience and certainty of a professional repair. While the resin repairs can always be corrected by a professional if your repair kit fails, your comprehensive auto insurance may cover the damage without cost on deeper scratches to prevent a claim for broken auto glass.
