Buffing and Polishing scratch resistant clear coat paint

By Kevin Farrell of Kleen Car Auto Appearance

Let’s go back to the days where the only type of paint system used on automobiles was single stage. Cars were painted in either a lacquer or enamel finish. These finishes differed from today’s clear coats in the fact that the pigmented paint of yesteryear was exposed to the elements and direct UV rays of the sun. Therefore, these paint systems would fade and oxidize and had to be buffed rather heavily to bring back the original finish. 

These paint systems differed slightly from each other, but both were basically fairly hard surfaces that required a detailer (or whatever they were called back then) to employ an aggressive buffing procedure. Many guys used very aggressive wool pads, compounds that felt like beach sand and very high speeds on a rotary buffer. Aggression was the norm, not the exception. Even when paint systems changed over to basecoat/clear coat in the early 80’s, the first generation of clear coat was very hard and required those similar buffing methods of a single stage system. Therefore, if a detailer did not know the difference in these paint systems, or was not aware that they were different, he generally would not make a critical mistake in buffing an early generation clear coat.  

Buffing methods had to change

When clear coat systems began to get softer in the late 80’s and 90’s, these aggressive methods of buffing had to be changed. No longer could a detailer use a “beach sand” compound and a very aggressive wool pad along with 2500-3000 RPM on a rotary buffer. This strategy would create too much damage to these clear coats such as burning, blistering, hazing and swirling. This era introduced more prominent use of orbital buffers, foam pads to correct a softer clear coated finish, special products that were “safe for clear coat”, and much lower speed on a rotary or even discontinued use of a rotary buffer. Detailers became afraid of the rotary buffer and began to rely on less aggressive methods of paint correction because of the fear of the problems previously mentioned.  

A blast from the past

These less aggressive methods for the most part worked if a detailer did not want to use a rotary buffer. An orbital could be made to do the job, albeit it would take longer and still not produce the finish of a correctly used rotary buffer. However, with the change now being made by more and more car manufacturers to scratch resistant clear coat, more aggressive methods need to be taken to correct these finishes. 

Today, there are products out there labeled as scratch resistant compounds and polishes. They are made more aggressive in terms of the type of abrasives used, the hardness of the abrasive, the shape of it, and the percentage of overall abrasives in the product. But there is more to the entire process than just buying a product. We have to know what’s going on with these scratch resistant clear coats as we buff them to get a better understanding of how to properly and quickly correct the finish.  

No more instant gratification

There are too many detailers, as well as body shop guys who demand instant gratification when they buff. They want to go back and forth once or twice and see all the scratches and imperfections just disappear. This obviously would save time but you have to be aware that the more aggression you use the more hazing, swirling and risk of burning you will have. Remember, clear coat of any kind is a form of plastic. If it’s heated too much, it will get very soft and then burn.  

With softer clears and older generation clears, it was easy to have a product and pad combination that would cut pretty fast and leave limited swirls and hazing. We could have almost instant gratification. This is why those aggressive products and buffing methods had to be backed down for use on the softer clear coats and many guys went to orbital buffers almost exclusively. With a scratch resistant clear, you have to buff it a little bit differently, but we first need to understand what’s going on with these clear coats as we buff them. 

SRC chemistry

There are basically 2 different types of scratch resistant clear coat. One is where the nanno particles of ceramic or fumed silica are migrated into the clear. Because of the extremely small or “nanno” 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 addition cross linking and hardness. Because these clear coats are called “Re-flow” or sometimes “self healing” in the fact that heat caused by sunlight will help correct minor (very minor) scratches, a detailer may think that creating heat is very good for this type of clear. Its not. It’s also not good for the ceramic or nanno particle clear coat either. Here’s why. 

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 its burning, the clear coat got too hot.  

With scratch resistant clear coats, if you heat them 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 in the fabric.   

However, the bonds of the scratch resistant clear coat can only be stretched so far. If the bonds are stretched too far they will remain stretched and cause damage to the bonds and 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” causing the existing scratches to 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 have a “wavy” look to it. So the more it gets heated, the more difficult it becomes to repair or correct deeper scratches.  

What needs to be done?

When 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. So 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 to this. 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 Tools

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 also needs to be kept below 1500 RPM as to not create too much heat. Remember 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 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 overthe scratches that were just driven deeper by over aggressive buffing.  

If you are too timid as in using an orbital buffer, a foam pad, a less aggressive product, 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 gage 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 seen myself and in talking with other detailers and body shop personnel, was not that they did not know what to do, but that they 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 100% correction. 

R&D of a 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 that comes into play 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 that even if you have a product that is aggressive enough, it can still sometimes be too aggressive in that it will remove the sand scratches but leave too much swirling and marring behind which is a problem in the remaining buffing steps.  

We were asked to create a compound for scratch resistant clear coats from somebody in the body industry. 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 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 how difficult it is to sand and buff.  

So as with our other projects in creating specific compounds and polishes, we set out on this one. This proved very difficult as we tried many abrasives and combinations and I kept finding that I did not like the cutting ability of most of them. We probably tried about 100 samples and most 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, a product that just doesn’t cut is the kiss of death for the product.  

This is why 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 so we could develop this type of product. I painted panels myself with the hardest version of scratch resistant clear and set out wet sanding. I received some scrap panels off factory vehicles from BMWNA as my contacts there proved very beneficial. I wet sanded and buffed those panels as well.  

I have lost count of the number of different samples and prototypes we have tried or the time we have put in. At the time of this writing we are 95% complete and will have a great scratch resistant compound and polish very soon. I wish I could say I had fun at all times doing this but I would be lying. At times it was very frustrating and humbling but we learned a lot and in the end we hope this helps everybody as these clear coats are here to stay.