New Clear Part II: Wet Sanding
Scratch-Resistant Clear Coat
By Kevin Farrell
| As seen on the right, the clear coat is not completely sanded. There is still a bit of gloss shown. This is because scratch-resistant clear is more difficult to sand. The left side is completely sanded with a more aggressive paper than you would normally need on a regular clear coat.
I hope you had your Wheaties and got a good night sleep, because sanding scratch-resistant clear coat
is not easy. As we discussed in
Part I (Auto Laundry News, February 2010) of this series of articles, these clear coats are much harder than conventional clears, so it makes sense that they will be much harder to sand.
As with any clear coat, you should be skilled in wet sanding and knowledgeable about paint thickness before attempting to
do this. You should also have a very good reason to sand any clear-coat surface. I speak to many customers, car enthusiasts, and detailers who throw the term “wet sanding” around willy-nilly and treat this as if it’s no big deal. Then, when they run into problems while sanding — sometimes to a catastrophic degree — they realize the project may have been too big for them to handle.
I have previously written other articles about wet sanding techniques, so that aspect will not be covered in this article. But if wet sanding is to be an option on any scratch-resistant clear coat, you have to understand what you will be in for. It will be more difficult
to remove material. As with sanding any clear coat, there should be good reasons for doing it. Examples would be a car with a deeper scratch, dirt nib stuck in the clear, etching, scuffs, etc. Reasons for not sanding clear coat — especially scratch-resistant clear — would be “swirls” or orange peel. I have had people call me requesting wet sanding or telling me that their car needed to be “wet sanded.” This is always a red flag for me. Since when do customers need their car to be sanded? They have heard this from either a detailer who just wants to oversell something, or picked it up doing Internet research and without fully understanding what wet sanding is all about.
HARD TO SAND THE HARD STUFF
| Grade and results: The 1200 paper on the left is more aggressive than the 1500 paper on the right. Both of these grades of paper are more aggressive than what a detailer might normally use, which would be 2000 grade
It is easy to remove excess material while sanding a more conventional clear coat. You can reach a point of breaking through into
the base coat very quickly if the wrong grade of sand paper is chosen, or if you are too aggressive. But if you know what you are doing, you can accomplish the task and then buff out the sand scratches rather quickly and get the job done. Scratch-resistant clear is the flipside of that situation. Removing material is very difficult. It just doesn’t want to come off. It seems as if you can sand forever, barely removing anything.
You may think this is a good thing because destroying the clear will be much more difficult. But you will need more aggression and force to remove the clear coat, and possibly a more abrasive choice of paper. This puts deeper scratches into the clear, which in turn will be more difficult to buff out. I have sanded some scratch-resistant clears with 1500 grade paper, and when I wiped the area clean I still had areas of shine, which means nothing really happened. I have seen this even with 1000 grit paper. You need some real elbow grease to remove material and get the imperfection out or sufficiently “shaved” down.
On most conventional clear coats, sanding with 1000 grit paper is an invitation for disaster. On a scratch-resistant clear, the surface almost seems to laugh at you and ask, “Is that all you got?” Removal of material will be that much harder and time consuming. So be wary of getting in too deep. When a customer wants orange peel removed or “swirls” wet sanded, you can’t be so gung ho as to sand an entire car with scratch-resistant clear. It will take forever
IDENTIFY A SCRATCH-RESISTANT CLEAR
In last month’s article I explained that there is no real way of knowing if a car has a scratch-resistant clear coat. The only company that designates this type of clear on a paint code is Mercedes. They use a “C” in front of the numeric paint code to signify this. Other than that, there is no chart or listing you can refer to to find out. Experience will play a part — having previously worked on cars that had scratch-resistant clear
coat. However, there is a little trick I can pass on that may help in the determination.
A scratch-resistant clear coat has a different “feel.” When you run the palm of your hand (always use your palm, not the back of your hand or fingertips) the surface will have more of a “grip” to it. It won’t feel quite as slick as a conventional clear-coat, even if it has some wax on the surface. Your palm won’t slide across the finish as easily, and it will almost have a hard, rubbery feel to it.
You will know even more once you get into sanding it. The piece of sand paper also won’t glide across the surface as well. It will have more grip and almost feel like its sticking to the surface. The amount of “milkiness” (clear coat) being removed won’t seem to be quite as much as with other clears you may have sanded. When you wipe away the residue, you also may see how little you have removed and there still may be a little gloss left to the finish, even if you were sanding with enough pressure. A paint thickness gage will further verify how much less material was removed. On conventional clear coats, the material comes off much easier and faster, and the worry about sanding through is usually the biggest fear. On scratch-resistant clears, you wonder how long is this going to take and whether you will actually
have to grind the stuff off.
ISN’T THIS ALL
|The dual-action sander is even more aggressive than sanding by hand — sometimes scratch-resistant clear coat requires it.
Not from where I am sitting. It is true that it will be harder to make a drastic mistake with scratch-resistant clear, but you will probably need a more aggressive paper to accomplish the job, which we will soon find out is a problem. If you were accustomed to using 1500 or 2000 grit, you’d better be ready to use 1200 or 1000 grit for the same types of problems on most cars.
If you do any kind of paintwork and need to prep a scratch-resistant clear-coated panel for refinishing, this is a problem also. In prepping a panel, you need to sand it to give the refinish material enough “bite.” If it’s too smooth or not sanded aggressively enough, the resulting refinish material may peel. I have had hoods and multiple panels that I have had to prep to refinish, and, boy, does that take some effort and a bunch more time to get done. Be aware of the extra time and effort required. This is why you should not jump into sanding an entire vehicle because a customer is unhappy with some orange peel or he thinks “swirls” need to be sanded out.
Here’s another thing to think about: If you are working outside, be very aware of the time the sand scratches are exposed to heat and direct sunlight. If you are sanding a black panel on a hot day, the heat created will want to make the clear coat re-flow and try to self-heal in most cases. These sand scratches are too deep for this process, so what happens is that the clear wants to fold over the scratch. This drives the sanding marks even deeper into the clear. This is fun, isn’t it? Oh, there’s more fun news: The rule of thumb is that you need to back out the deeper sand scratches with lighter grades of paper. So on conventional clears, if you started with 1500 grit, you will finish with 2000 grit and be ready to buff. You always want to reduce the level of sand-scratch marks that are left in the finish so they are easy to buff out. While sanding scratch-resistant clear, you will probably need a more aggressive paper to begin with such as 1200 or 1000 grit. But backing out these sand marks is that much more difficult and time consuming. It’s also very important to make sure that you actually do get backed out to 2000 grit marks, or the buffing process becomes that much more challenging.
YOU CAN DO IT
Now sanding scratch-resistant clear is not impossible. It is not the doom and gloom that I may have made it out to be — but it is more difficult to do. You need to know exactly what’s going on at all times and you still need to be careful. You need to give yourself more time to go through the entire process as the sanding is more difficult. Don’t forget, at the end of the sanding stage, you still need to buff out the sand scratches in this very hard clear. This is no easy chore in itself.
In Part III of this series of articles, we will discuss how to buff this type of clear and what different methods and products may have to be used in the process.
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.