Here's a short blog I put out on my site a while back based on my experience and practice prepping and coating glass. The true key to success IMO/IME is getting the glass perfectly clean so water clings to it and doesn't bead. That means you've removed EVERYTHING and are down to virgin glass. I also am adamant about replacing wipers. As part of my process when customers pay for a window treatment, I build in replacement wiper inserts as part of the cost and replace them for them at the time of the detail.
Safe Driving Starts with Good Visibility
Glass Coatings are a great alternative to OTC Rain-X or AquaPel products. The advantage they bring is a more consistent performance free of streaking and the length of time they last. On windshields coatings typically last 6-9 months with upwards of a year is not uncommon. The main point of degradation comes from wear and tear from wipers and the fact that the front of vehicles is constantly being pelted by contaminants that wear away at the protection.
Key to Success
The key to successfully applying a glass coating lies within the preparation of the surface just as it does with paint coatings. Most all the complaints and issues I see with glass coatings can be traced back to improper preparation which leads to uneven application, thus wiper shudder, or a less than prepared surface that leads to contaminants still being present and again, causing wiper shudder or streaking. Lastly, if the glass isn’t prepared the product can not bond effectively thus it simply will not last.
Remove the Contaminants
When preparing for glass coatings, start when washing your vehicle. Use glass clay or a synthetic clay-mitt to remove the surface contaminants such as dirt, grime, road film, tree sap, etc that will simply not be removed by washing alone. I prefer synthetic mitts simply because they are more effective and last longer. Do NOT use regular paint formulated clay as it will tend to get trapped in the microscopic pits of the glass and thus impeding proper bonding leading to the above noted issues. Once trapped, it’s also very difficult to remove.
Once the vehicle is cleaned and dried, the key then becomes getting down to the virgin glass under what still will be on there which includes timeless amounts of road film and sealants. If you notice the water isn’t “clinging” (see top right image) to the window as shown in this photo and instead is beading or leaving streaks of water, then it’s not ready to be coated. Once the glass is cleaned and water clings, it's so thick you can cut through it with a water blade and yet the surface tension will still hold the surrounding water in place. That's a good thing!
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What’s next is to use a fine glass polish and a polishing pad specifically for glass. This will safely remove any remaining layers of film and open up the pores from pitting over time so that the product can fill in those marks and bond effectively leaving a fully level surface that is hydrophobic and super smooth. I like Adam’s Brand Fine Glass Polish and their corresponding glass pads. Adam’s is super easy to wipe off and again, unlike traditional polishes meant for paint, will not fill in the pores that are now exposed.
CarPro CeriGlass is another good alternative but overkill for coating applications and if not used in the hands of a skilled person will actually scour or scratch your windows, so consider your experience level and understanding of the product before attempting to use it.
Final Step
Once the polishing is done and wiped away, I like to use denatured alcohol and some paint prep spray to give it a final once over to remove all traces of anything. From there, a final wipe down with a good window cleaner to leave a perfectly smooth and clean glass layer ready for your coating is all that’s needed. I like Stoner’s Invisible Glass as my go-to cleaner for both inside and outside of windows.
Now you’re all set and ready to apply your window coating of choice. Just be sure to follow their respective instructions closely and going forward, avoid using any detail sprays, waxes or sealants on the windshield portion of the vehicle with wipers as they can lead to shuddering or poor performance over time. On side windows, I’m okay with spraying them but here too, anything you apply to the glass will tend to overpower the properties of your glass coating thus leading to more beading vs sheeting.
Good luck and enjoy your now clear vision!
