Koch Chemie Compounds: Which Cut for Which Job
Every week someone comes into the store, picks up a bottle of Heavy Cut, and asks if it will take care of the swirls on their car. Most of the time the answer is that it will, and that it is the wrong bottle for the job. Heavy Cut will remove the swirls and leave you with a haze that needs a second and sometimes a third product to clear up. The lighter bottle next to it would have removed the same swirls in one pass and finished clean.
Choosing the right compound is the single biggest time saver in paint correction. It is also the difference between a car that looks good in the garage and a car that looks good under the sun. We run Koch Chemie in the shop because the range is small and each product does a defined amount of work. There is very little overlap, so once you know what each bottle does the decision makes itself.
This post walks through the four Koch Chemie compounds and polishes we stock, the Rupes pad we pair with each one, and the way we decide which one a given panel needs. I have also answered the question I hear most, which is what the difference between a compound and a polish actually is.
The four Koch Chemie compounds on our shelf
Heavy Cut H9.02 is the coarse compound. Koch Chemie built it for fast reworking of heavily weathered paint, deep scratches, and sanding marks up to 1,200 grit. It is free of silicone oil, so it does not fill defects and hide them. The abrasive is very uniform, which is why it cuts hard and still leaves a decent gloss for a coarse compound. It works for long periods without sticking and with very little dust. H9.02 is the replacement for H9.01 and gives the same cut with a higher gloss finish. It works on soft paint and on scratch resistant paint.
Fine Cut F6.01 is the middle step. Koch Chemie rates it at a cut of 6.0 and a gloss of 7.0. It removes car wash scratches and similar wear quickly and takes out 2,500 grit sanding marks. On medium to heavily weathered paint it is often the only compound we need. It is set up well for scratch resistant clear coats.
Micro Cut M3.02 is the finishing polish. Cut is rated at 3.2 and gloss at 9.0. It is built to permanently remove streaks, holograms, fine scratches, and sanding marks to 3,000 grit on every paint system. Koch Chemie says the defects are removed mechanically and not covered over, and that matches what we see under inspection light. It is very economical. A small amount goes a long way.
Micro Cut & Finish P3.01 does the same cutting work as M3.02, with a rated cut of 3.2 and gloss of 9.5, and adds a layer of protection in the same step. It contains carnauba wax and silicones that stay on the paint. That makes it a one step finish for a car that is not getting a coating afterward. For a car that is getting coated, we use M3.02 and skip the wax.
Compound vs polish, what is the difference
The words get used loosely, so here is how I use them. A compound is an abrasive liquid with enough cut to remove real defects: deep scratches, sanding marks, heavy oxidation, years of automatic car wash damage. It levels the clear coat down to the bottom of the defect. Because it removes material quickly, it usually leaves its own fine marks behind, and those need a second step.
A polish is a lighter abrasive that removes very fine defects and refines the surface to a high gloss. It takes out the haze the compound left, along with holograms and light swirls. It removes very little material. On a well kept car a polish is often all that is needed.
The Koch Chemie numbers make this concrete. Heavy Cut is the compound. Fine Cut sits between the two, with enough cut to fix most real world wear on its own. Micro Cut is the polish, and Micro Cut & Finish is the polish with protection built in. The gloss numbers move the opposite direction from the cut numbers, and that is the whole trade off in one line.
The mistake people make is starting with the highest cut. The right approach is the least aggressive product that fixes the defect. Test a spot with Micro Cut. If the defect is still there, step up to Fine Cut. Only go to Heavy Cut when Fine Cut is not getting it done. You remove less clear coat that way and you spend less time finishing.
Pads: which Rupes foam goes with which compound
Koch Chemie's own recommendations lean toward rotary polishers, lambskin, and their own pads. In our shop most correction work happens on Rupes random orbital and gear driven machines, and we run the Rupes DA foam pads. These are the pairings that work for us.
Rupes DA Coarse cutting pads in blue go with Heavy Cut H9.02. The open cell foam removes mild to severe defects and works on both random orbital and gear driven tools. This is the pairing for a car that has been through years of tunnel washes or has sanding marks from a paint repair.
Rupes DA Fine pads in yellow go with Fine Cut F6.01. Rupes calls this the most versatile foam in the range, and I agree. It removes moderate defects and finishes well enough that on many cars it is both the correction pad and the finishing pad.
Rupes DA Ultra Fine pads in white go with Micro Cut M3.02 and Micro Cut & Finish P3.01. This is the finest foam Rupes makes, built for very high gloss finishing and for soft or haze prone paint. It is also the pad we use to spread sealant when no correction is needed.
One rule from Koch Chemie worth following. Keep pads dedicated to one product. A pad that has run Heavy Cut has coarse abrasive in the foam, and it will contaminate a finishing polish. Mark the pads or keep them in separate bags.
How we decide which cut a panel needs
The decision starts under the light, and I mean a proper inspection light, which I wrote about in reading your paint: what inspection lighting shows. Shop lighting hides most defects. A handheld light held at a low angle shows the swirls, the deeper random scratches, and the holograms left behind by someone else's rotary.
Then we do a test spot. A two foot square on the hood or a door, taped off, with the mildest combination we think will work. Polish it, wipe it with a panel cleaner to strip any oils, and check it under the light. If the defects are gone and the finish is clear, that is the process for the whole car. If defects remain, step up one compound and try again. If the defects are gone and the finish is hazy, the compound was right and it needs a finishing step with Micro Cut.
Swirls and light wash marring on a maintained car almost always come out with Micro Cut on a white pad. Random isolated scratches you can barely catch a nail on usually need Fine Cut on a yellow pad. Holograms from a bad polish job are a Micro Cut job, because they are shallow and only need refining. Sanding marks from paint work need Heavy Cut on a blue pad first, then Fine Cut, then Micro Cut. On the S4 respray we did last year that was the full three step process on every panel.
Pick the defect, get the starting point
Here is the same decision as a shortcut. Tap the defect you are looking at under the light and it shows the bottle and pad we would start with, and where to go if the test spot does not come out clean.
Swirls and wash marring
If the test spot still shows them
Step up to Fine Cut F6.01 on a yellow pad, then finish with Micro Cut on white. Years of tunnel washes usually land here.
Why
Swirls are shallow. A finishing polish levels them without taking clear coat you do not need to lose, and it finishes clear so there is no second step.
Random light scratches
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Start hereFine Cut F6.01 on a Rupes Fine yellow pad. The scratches you can barely catch a nail on.
If the test spot still shows them
Heavy Cut H9.02 on a blue pad, then Fine Cut, then Micro Cut. If your nail catches hard in the scratch, it is through the clear and no compound will remove it.
Why
Fine Cut has enough cut for real wear and often finishes clean enough to skip a polish step. It is the bottle we reach for most on German clear coats.
Holograms and buffer trails
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Start hereMicro Cut M3.02 on a Rupes Ultra Fine white pad, worked until the film goes transparent.
If the test spot still shows them
Holograms almost never need more cut. If they persist, the problem is usually a contaminated pad or product that has not broken down. Fresh pad, less product, slower passes.
Why
Holograms are the shallowest defect there is, left by a rotary that was not finished properly. They only need refining, not leveling.
Sanding marks after paint work
Then
Fine Cut on yellow to clear the haze Heavy Cut leaves, then Micro Cut on white to finish. Three steps on every panel, which is what the S4 respray got.
Why
Sanding marks are the one defect that justifies starting coarse. Anything lighter will spend an hour per panel and still leave the scratch pattern.
Working the product correctly
A few habits from the bay that make Koch Chemie compounds behave. Prime a new or dry pad with a little polish first, which Koch Chemie specifies for Micro Cut. Spread the product across the section with the machine off, then work it crosswise at medium pressure. With Fine Cut, start with more pressure at lower speed, then back off the pressure and raise the speed to bring the gloss up. With Micro Cut, work it until the film goes transparent, which means the abrasive has broken down fully. Wipe the residue with a clean, soft microfiber that will not scratch. Then check under the light again before you move on.
If the car is going to be coated afterward, every panel gets a wipe with Nanolex EX to strip polishing oils so the coating can bond.
Koch Chemie compound questions we get asked
Which Koch Chemie compound removes swirl marks?
Micro Cut M3.02 on a fine finishing pad removes swirls and holograms on most cars. Heavier wash damage may need Fine Cut F6.01 first.
Can I use Koch Chemie Heavy Cut with a DA polisher?
Yes. Koch Chemie's own guidance is written around rotary machines, but we run H9.02 on Rupes random orbital and gear driven tools with the blue coarse pad every week.
Do I need to polish after Heavy Cut?
Yes. Koch Chemie recommends following Heavy Cut with Micro Cut M3.02 or Micro Cut & Finish P3.01 for the best finish. On most cars we put Fine Cut between them.
What is the difference between Micro Cut and Micro Cut & Finish?
Both have a rated cut of 3.2 and remove the same defects. Micro Cut & Finish adds carnauba wax and silicones for protection and a slightly higher gloss. Use Micro Cut if the car is getting a ceramic coating.
Does Koch Chemie Fine Cut work on hard clear coat?
Yes. F6.01 is described as perfectly coordinated for scratch proof paint, and it is the compound we use most on German cars with hard clear.
Can Koch Chemie compounds remove sanding marks?
Heavy Cut removes sanding marks up to 1,200 grit, Fine Cut removes 2,500 grit marks, and Micro Cut removes 3,000 grit marks.
Where to start
Paint correction gets easier when the products stop overlapping. With the four Koch Chemie bottles and three grades of Rupes foam, every defect we see in the shop has a clear starting point, and the test spot tells us if we guessed right. Start mild, check under a real light, and step up only when the paint asks you to. If you would rather see it done before you try it, stop by the shop on a correction day and watch.
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The coarse step Koch Chemie Heavy Cut Compound H9.02 $79.99 · silicone oil free, removes sanding marks to 1,200 grit, pairs with the Rupes blue coarse pad · ships from Norwood, NJ Also in this post: Fine Cut F6.01, $75.99 · Micro Cut M3.02, $74.99 · Micro Cut & Finish P3.01, $26.99 · Rupes DA pads in blue, yellow, and white from $6.99. |
Phil