Wet sanding and buffing scratch resistant clear coat 

By Kevin Farrell of Kleen Car Auto Appearance

 

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 our last article, 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 many detailers who throw the term of 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 to handle. 

I have written other articles before regarding wet sanding techniques and such, so that will not be covered here 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 of these 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 because of “swirls” or orange peel. I have had people call me requesting or telling me that their car needed to be “wet sanded”. This is always a red flag for me. Since when does a customer need their car to be sanded? They have heard this from either a detailer that just wants to oversell something, or a customer doing internet research and not fully understanding what wet sanding is all about.  

Harder to sand the hard stuff

I have spoken and written before how easy it is 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 still accomplish the task and then buff out the sand scratches rather quickly and get the job done. However, the flip side is scratch resistant clear. Removing material is very difficult. It just doesn’t seem to want to come off. It seems you can sand forever, barley 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. In turn this puts deeper scratches into the clear which in turn will be more difficult to buff out. I have sanded some scratch resistant clears before 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 with 1000 grit paper also. 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?” So the removal of material will be that much harder and time consuming. So be wary of getting in too deep. When a customer wants their orange peel removed or their “swirls” wet sanded, you can’t be so gung ho to sand an entire car with scratch resistant clear. It will take forever 

How will I know if the clear is scratch resistant?

In my previous article I stated that there is no real way of knowing if a car has 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 to find out. Experience will play a part in knowing what you have previously worked on that had scratch resistant clear coat. However there is a little trick and tip I can give you 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 a slick, even if it has some wax on the surface. Your palm wont slide across the finish so easy 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 wont seem to be quite as much as other clears you may have sanded. When you wipe away the residue you also may see how little you have removed and that there still may be a little gloss left to the finish, even if you were sanding with enough pressure. A paint thickness gage will also 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 will I actually have to grind this stuff off?  

Isn’t this all good news?

Not from where I am sitting. It is true that it will be harder to make a drastic mistake with SRC, but you will probably need a more aggressive paper to accomplish the job which we will soon find out is a problem. On most cars if you were used to using 1500 or 2000 grit, you better be ready to use 1200 or 1000 grit for the same types of problems.  

If you do any kind of paint work 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 it will take to get something done. 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. What that does is drive 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 SRC, you will probably need a more aggressive paper to begin with such as 1200 or 1000 grit. But backing down 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 down to 2000 grit marks or the buffing becomes that much more challenging. 

Now sanding SRC is not impossible and it’s not the doom and gloom that I may have made this 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 your self more time to do this entire process as we have sent hat the sanding is more difficult, but don forget we still need to buff out the sand scratches in this very hard clear. This is no easy chore in itself, so let’s look at buffing SRC. 

In our final article on scratch resistant clear coat, we will discuss how to buff this type of clear and what different methods and products may have to be used.