UHS Clear Coat: How to Correct Modern Hard Paint
If you’ve ever spent a frustrating late night at the workshop throwing every heavy-cut polish you own at a modern car and getting nowhere, there’s a good chance you’ve met UHS clear coat.
Ultra High Solids clear-coat is now becoming the norm on modern vehicles – some European manufacturers have had the technology for decades – and while it’s great news for the car’s owner, it’s added a whole new branch to the detailing knowledge tree. Correct it the way you’d correct “normal” paint and it will fight you every step of the way.
What is UHS clear coat?
The technology itself is relatively simple to understand. The standard clear-coat we’ve known for years is still there in the chemistry, but the addition of micas, silica and other “ceramic” components gives it a very different character. The result is a high-solids clear coat, designed specifically to protect the colour basecoat beneath it and give the owner a harder-wearing, more scratch-resistant, longer-lasting finish.
Image courtesy of PPG
Good news and bad news for detailers
For a detailer, this cuts both ways. The good news is that when it’s corrected and protected properly, UHS clear-coat can give years of low-defect finish – which gives real traction to your protection services and builds trust when you’re quoting estimated coating lifespans. The bad news is that the surface is notoriously tricky to correct once it’s scratched or marred. Its hardened nature makes short work of diminishing-abrasive (DAT) polishes, and it often reacts badly to heat.
Why heat is the wrong answer
For most detailers, if a polish and pad combination is struggling to cut back defects, the instinct is to step up the aggression – a harder pad, a heavier cut. On the vast majority of cars up to the mid-2000s, that works. On UHS clear-coats, and especially anything in the “cerami-clear” category, it can actually make things worse. Some detailers swear by using heat to beat the hardness, but the science points the other way.
The first problem with building heat is the obvious one: risk of damage. Monitoring your temperatures is the single biggest priority in minimising the chance of harming the surface – heat is what you’re trying to control, not generate.
The second problem is subtler. High-solids clear-coats tend to expand quickly when heated. Cut defects from a UHS surface using the “hot” method and you can create a false correction – you’re polishing the expanded surface, not where it will come to rest. When it cools, or you wipe it down with a paint cleanser, it contracts and the defects rapidly reappear. This is sometimes called thermal rebound, and it’s behind a lot of those frustrating late nights: the heat from a heavy polish expands the layer and blasts through the diminishing abrasives in no time, often taking your favourite wool or foam pad with it. So if heavy cutting doesn’t work, and heat through machine speed or arm movement doesn’t work, where do you go next?
The answer: slow it down, cool it down
Wet sanding is one option – if you fancy several more days chasing sanding marks back out. The better answer is to slow down, cool down and relax. UHS clear-coat responds very well to medium-abrasive, SMAT-derived polishes, and refinement in stages. Combine that with the right pad – ideally an open-cell, medium-hard foam – and the only things left to adjust are your machine speed and your temper.
A lower machine speed keeps the panel and pad temperature as low as possible, avoiding the expansion and rebound, and gives the lubricants and abrasives in the polish longer to do their work. You can counteract the reduced cut from the lower speed by slowing your arm movement a little too, which lengthens the time the polish spends working each area per pass while keeping temperatures down. Expect this to take perhaps twice the passes you’re used to on a normal 2K clear-coat – but that’s still half the time of going into battle with a bottle of “TurboGRIT 9000” and a wool pad from 1978.
As you move to the finishing stages, add some half-steps into your pad and polish reduction: for stage two, switch to a softer pad; for stage three, switch the polish.
Getting to grips with it
Reading – and correcting – modern hard clear-coats is exactly the kind of hands-on judgement that’s difficult to learn from a bottle label or a video. It’s one of the many topics covered on our Career Development courses, and it’s a core part of our Advanced Polishing 1-to-1 course. If you’d like a steer on machine choice before you tackle it, our guide to dual action vs rotary polishers is a good primer.
