New Clear — Conclusion: Buffing & Polishing
Scratch-Resistant Clear Coat
By Kevin Farrell
In the April 2010 issue of Auto Laundry News (Part III of this series of articles), we discussed the changes in buffing methods necessitated by the new scratch-resistant clear coats. This month, we conclude the series with a brief recap of scratch-resistant clear coat chemistry and a look at the tools and products you may have to use in the buffing process.
There are basically two different types of scratch resistant clear coat. In one, nano particles of ceramic or fumed silica are migrated into the clear. Because of the extremely small or “nano” size of these very hard and very light particles, they rise to the very top portion of the clear coat giving it its scratch resistance. With particles that are this hard, more aggressive methods will be needed for paint correction.
The other version of scratch resistant clear coat is of the “re-flow” version. This is the hard urethane, hard durometer clear coat with a hydrogen bond that adds cross-linking and hardness. These clear coats are called “re-flow” or sometimes “self healing” because heat caused by sunlight will help correct minor (very minor) scratches. Because of this, a detailer may think that creating heat is very good for this type of clear. It’s not. It’s also not good for the ceramic or nano particle clear coat.
Heat is the Enemy of SRC
We should already know that excess heat can burn, blister, haze, and cause excessive swirls. We do need to create a little bit of heat when buffing to burnish the clear correctly and help restore a deep gloss and clarity to the finish. But how much heat is too much? As always, if you can’t touch the surface without quickly removing your hand because it feels like it’s burning, the clear coat got too hot.
If you heat scratch-resistant clear coats too much, you will make them “swell.” Now in theory this sounds good. The self-healing or re-flow effect of the clear should come into play and help repair the imperfection. The clear would heat up, then flex, expand, and contract. This would make a very minor scratch go away. It’s the same principle as taking wrinkles out of clothes. The material is heated, it then expands, contracts and flexes, causing the crease or wrinkle to disappear.
However, the bonds of the scratch-resistant clear coat can only be stretched so far. Stretched too far, they will remain stretched and cause damage to the density of the entire system. It also will get too hot, which will cause the clear coat to expand far too much and “open up.” As a result, the existing scratches will be driven even deeper into the clear coat, thus making the scratch that much harder to get out. This can also make the clear coat take on a “wavy” look. So the more it gets heated, the more difficult it becomes to repair or correct deeper scratches.
What Needs to be Done?
When a scratch-resistant clear coat is scratched too deep, it becomes fractured. This appears as a deeper white scratch. The depth of this type of scratch is beyond the point of self- healing or -repairing. Now your work is cut out for you.
Patience is the key. There is no instant gratification in repairing scratch-resistant clear coat. Sanding it will take longer and buffing it will take longer. Here’s the catch. If you are using a regular polish or a very light compound, you may want to tell the customer to pick up his car a week from next Friday, as you may be buffing it that long. You will need a more aggressive product and a more aggressive buffing pad. Everything needs to be more aggressive, and you can’t be afraid or timid. The clear-coat-film thickness will still be about the same as a conventional clear (no more, no less), so care must be taken not to blister it or rub through. But if you are too timid you will never get the scratches out.
However — and there is always a “however,” it seems — if you get far too aggressive you can still haze and swirl a scratch resistant clear very easily; it is not immune. You can’t just go out and buy an old time beach sand compound and a super aggressive wool pad and go to town. While you may get the scratches out, you will leave a much deeper swirl that will have to be addressed in the remaining buffing steps.
The buffing product will need to be fairly aggressive, but not “old school” aggressive. The pad will probably have to be wool. Yes wool, if you want to get the deeper scratches out and do it before next Friday. A foam pad — even the more aggressive, firmer foam pads — will create too much heat and not cut enough. I prefer a medium duty wool pad as it will cut but not leave horrible swirls and hazing in the scratch-resistant clear. Also, the job will need to be done with a rotary buffer. An orbital just won’t “cut” it on this type of clear coat. The buffer speed needs to be kept below 1500 RPM to prevent creating too much heat. Remember that heat will be the enemy and too much heat will sabotage the job, not accelerate the job.
Again patience is the key. If you let the product and the pad do the job while maintaining even pressure throughout, you will be able to cut the scratch resistant clear. The “shaving” of the clear coat will take place and the swirling and hazing can be minimal if the correct techniques are used. If you are too aggressive from the start and want things to happen very quickly, you will overheat the clear, open it up, and drive the imperfections and scratches even deeper. The re-flow effect of some scratch resistant clears will make it want to re-flow back over the scratches that were just driven deeper by over aggressive buffing.
If you are too timid and use an orbital buffer, foam pad, a less aggressive product, and/or less pressure and speed, you may eventually get the scratches out but it will take considerably longer.
It’s Not All Doomsday
It’s not impossible to work on these clear coats. As stated, some will be much harder than others and only continued experience buffing different cars will give you a good gauge of what to expect. Yes, it will take more to severely mar a scratch-resistant clear, but once it has those deeper scratches you must have the solution to get them out. The frustration that I have felt myself — and have heard other detailers and body-shop personnel confirm — was not because I did not know what to do, but that I did not have a good enough product to get the scratches out of a scratch-resistant clear coat. The process would take a while for a 100-percent correction.
AN SRC COMPOUND
If you do a lot of wet sanding, it will get frustrating if you run into very hard scratch-resistant clears. When there are sand scratches in multiple panels that have to be removed, you will need a very good product and a game plan to get rid of them. There are a few variables and frustrations to deal with that will drive you crazy if you are not ready.
One frustration is that the clear will be difficult to sand because of its scratch resistance. Usually I have to compensate with a courser grade of paper than what I wanted to start with. Once it’s sanded the monumental task of buffing out the sand scratches on multiple panels or the entire vehicle remains.
Another huge frustration is trying to buff out these sand scratches and not getting anywhere because the product doesn’t have enough bite or aggressiveness to fully remove them. Yet another frustration to contend with is having a product that is aggressive enough to remove the sand scratches, but leaves too much swirling and marring behind, which is a problem in the remaining buffing steps.
Many of the refinish clears are now being made in a scratch resistant variety to meet the warranty on the car manufacturer’s specifications. If a vehicle needs to be refinished and already has a scratch resistant clear coat, the car manufacturer mandates that the refinish clear meet the same specifications to remain under warranty. Therefore more and more body shops are coming across the same problems regarding sanding and buffing the clear.
Some in that industry asked that a compound be created specifically for scratch-resistant clear coats. This has proven to be very difficult; we tried many abrasives and combinations, but did not like the cutting ability of most of them. Most of the roughly 100 samples worked very well on conventional clear and some lighter grades of scratch-resistant clear coats, but on the very hard versions, nothing wanted to cut. And for a body-shop guy, inability to cut is the kiss of death for a product.
I had to learn more and more about these scratch-resistant clear coats. I needed to know the chemistry behind them and what I was in for. I painted panels with the hardest version of scratch-resistant clear and set out wet sanding. I received some scrap panels off factory vehicles from BMWNA, and I wet sanded and buffed those panels as well.
I have lost count of the number of different compound samples and prototypes I’ve tried; yet a great scratch-resistant compound and polish eludes us still. Soon, I hope, soon. I wish I could say I was having fun all the time while doing this, but that wouldn’t be true. At times it was very frustrating and humbling, but we learned a lot and in the end we hope this helps everybody; these clear coats are here to stay.
Kevin Farrell owns and operates Kleen Car (www.kleencarauto.com), a full-service auto-detailing business located in New Milford, NJ. Kevin is also an instructor for a detailing program he developed for, and in conjunction with, BMW of North America. His background includes auto dealership experience and training through DuPont, General Motors, and I-Car.