top of page

Why would anyone remove undercoating?

There are a few reasons why you might want to remove undercoating from your car. The first and most obvious reason Undercoating is designed to protect your car's undercarriage from rust and corrosion, but it can also trap moisture. If there were any flaws in the undercoating process small pockets could have formed between the car surfaces and the backside of the undercoat product. Any cracks in this coating might allow ambient humidity, moisture, creep into the void. This moisture can then cause rust to form, even if your car is not driven in harsh winter conditions.

Following are two examples of wonderfully cared for vehicles that incurred two different problems. Both resulting in the necessary removal and reapplication of corrosion protection. The first is a 1991 Cutlass Calais W-41. Thirty year old, pampered vehicle only driven twenty thousand miles in it's young life. The owner brought it to me to have the engine bay and wheel wells freshened up for Detroit's Radwood show. We put it on the lift and looked at the bottom just to see if there wasn't something being overlooked. The owner said I probably would not find anything to do on the bottom of the car as it was so well cared for. He was right except for the subframe around the grease fittings. Very well cared for vehicle. Very well greased. Unfortunately some of the products used to keep our cars running well compromise the coatings used to stop rust and corrosion. In this case the copious amounts of grease applied weakened the undercoating leaving those areas vulnerable to future corrosion or rust.

We used dry ice blasting to remove the old, damaged coating. Using dry ice to clean the area means there is no residual cleaning product, or media, to clean after removal of coating. It is ready to recoat immediately.

Afterwards we applied some fresh undercoat supplied by Dinitrol. That weekend the car won it's category at the show. I don't think the car would have won without Co2 Auto Renew going the extra mile by looking for areas that may be compromised. Removing and replacing the old undercoating will also help the vehicle will last much longer.

The second example is a 1965 Buick Riviera. Another well loved, painstakingly cared for car. The owner brought the car to Co2 Auto Renew to have the engine bay, wheels, frame and suspension cleaned. He was very adamant that it wasn't necessary to remove undercoating as his car hadn't even seen a drop of rain in decades.

As I was cleaning the brake drums some compressed air "blow by" at 60 psi caused a big (5"x6") area of undercoating to fall off. Three feet away from the compromised spot at 60 psi isn't any more pressure than that created by air flow driving at slower freeway speeds, but it came dislodged, luckily, telling on itself.

(yes, I know htis word isn't spelled htis way....caught it too late)

Once we removed all of the undercoat we could see just how much surface rust was hidden by the undercoating. In all fairness it wasn't going to rust through anytime soon. However, I think with the value of collector cars constantly rising it is becoming very important to protect your investment. I think a vital part of protecting your investment is removing old undercoating and finding out just what the condition of the whole vehicle is. The picture below is after a pretty thorough dry ice blasting. As a result the area doesn't look as bad as the dry ice blasting does a pretty good job of removing some of the rusty appearance. You can still see from the brown staining are where the surface rust was.

Here are a couple more examples of the undercoating hiding areas that were not problems yet, but there is no doubt this failing coating was going to allow problems to start. The low pressure used(25psi) for the dry ice cleaning was not the what removed the paint. It was already beginning to fail prior to cleaning evidenced by the missing paint exposing the bare metal. Also, the slight discoloring is usually a good indication it is starting to hold moisture or other substances possibly picked up off the road.

The owner wanted to keep tabs on any future problems on the bottom of this car so we coated it with clear undercoating. This way he can bring his car back once a year and we can give it a comprehensive inspection. If anything looks questionable we can remove any previously applied coating with dry ice and reapply to make sure everything is sound.

There are a couple more reasons to remove old undercoating. If your car starts making strange noises or you notice other problems, it can be more difficult to diagnose the problem if there is old thick undercoating on the undercarriage. This is because the undercoating can muffle the sound of the problem and make it difficult to see the problem visually.

Old coatings can make it much more difficult to fix your car. If you ever need to work on your car's undercarriage, it will be much easier if the undercoating is removed. This is because the undercoating can make it difficult to access certain parts of the undercarriage and can also make it difficult to remove bolts and other fasteners.

Old undercoating can contain harmful chemicals that can pollute the environment. As your vehicle ages failed coating can be jarred loose leaving pieces of undercoating everywhere you drive.

Black, or non-transparent undercoating should be removed and replaced every 5 years or so. If the undercoating on your car is damaged or cracked, it will no longer be able to protect your car from the elements. This could lead to rust, corrosion, and other damage. The undercoating is old and needs to be renewed. Undercoating can break down over time, so it's important to have it renewed every few years. This will ensure that your car is properly protected from the elements.

Clear undercoat may not be the most attractive in the end, but it is probably the best way to monitor these old "survivor" or "preservationist" vehicles. Clear is probably the most cost effective way to protect these old treasures because you don't have to remove everything to see what may, or may not be hiding under the corrosion protecting coatings.

The goal isn't just to slow down aging. The goal is that no part of your car ages, or wears faster than others. How useful, or valuable, is a vehicle that looks fantastic driving down the road, or in your garage when the suspension, frame or bottom panels are slowly rotting behind some uniformly applied and seemingly impenetrable undercoat. You wash, wax, ceramic coat and apply paint protection film(PPF) to keep the exterior paint from aging. But what are you doing to manage the hidden, or unnoticeable areas? There have been great advancements in protection for exterior finishes in the automotive industry that have had amazing results. Now with dry ice cleaning(blasting sounds rougher than what we really do) we can clean all the unmentionable areas that no one looks at, or talks much about and address any problems for they become bigger, more costly problems. The addition of dry ice as a tool for vehicle care and preservation will help many cars survive for a long, long time.

Clean cars get better mpg,


335 views0 comments

Recent Posts

See All


bottom of page