Foreword: Rather than to address “undercoating” as a general topic of discussion, I’ve tried to keep the focus upon undercoating as it related to Volkswagens through 1979 and as it relates, now, to the vintage Volkswagen hobby.
Undercoating has around for years and years in the world of vintage Volkswagens.
The theory behind undercoatings is that a barrier could be created to prevent the infiltration of moisture. Undercoatings themselves had no rust-inhibitive qualities. They simply have been intended as a barrier.
VW dealerships sold the service to new car buyers as a preventative measure to guard against rust. It was a money-making operation and dealers loved it. Especially was it offered in the colder climate States and especially where salt was used on icy roadways.
Recently, I spoke with a former VW trained specialist. He described the undercoating procedure as he observed it. He said that the dealership where he worked had one bay with a lift, “in a dark corner”, where the “nasty” undercoating took place. He told me that it was part of a money-making effort by dealerships in the make-ready department. Undercoating was applied using a hose and gun working from a 30 gallon barrel of material.
I have had my doubts over the years about its effectiveness in sealing the undersides of a vehicle as a moisture barrier. Here’s why. I was in the painting industry for almost 30 years. If there is a coating, I likely have seen it or read about it. In my experience, despite all claims to the contrary, coatings will fail. There is no “eternal” coating. I’ve heard claims that “you’ll never have to paint again”. Why can’t this be true?
It can’t be true because of expansion-and-contraction problems. When the base material—wood, metal, plastic—expands or contracts, the coating is going to suffer, eventually. Some coatings are better suited than others. But the fact of the matter is that coatings fail.
Metals, especially, are given to fluctuations from heat and cold. They will expand and contract more, and more quickly, reacting to weather and usage conditions.
What’s another problem? It’s the fact that the underside of a vehicle is not a continuous sheet of metal. Not at all. The undersides of vehicles are composed of pieces that have been fitted to form a unit. This could be through a continuous weld or spot-welding or with nuts and bolts and washers. There are joints. Every place where there is a weld or a nuts-and-bolts joint, expansion rates will differ.
As well, the application of undercoatings must completely encase all of this in order to form a viable covering—it must be seamless. This doesn’t happen.
The next issue is that undercoatings historically were shot onto factory painted surfaces. In order for a coating to adhere, there must be the possibility of adhesion. Slick surfaces will not offer such adhesion possibilities. As a result, I have been able to remove portions of undercoatings on Volkswagens simply by using compressed air. Sometimes, I have been able to remove it in sheets, simply because of the lack of adhesion. I can imagine that vibration over the years helps to loosen poorly adhered coatings.
Also, the spraying of undercoating cannot reach all places and the places which it does reach often are coated unevenly due to the nature of the operation.
While coatings do not adhere well to many painted surfaces, they may adhere to other surfaces tightly—such as the transmission, the horn, shock absorbers, brake lines, etc., etc.—parts which need little protection. Now, these parts are covered –at least parts which the spray can reach.
Another factor to understand is that coatings shrink as they “cure”. Shrinkage does not happen immediately. Some coatings may take hours or even days to complete their “cure time”. Generally the thicker the coating, the longer the cure time. Shrinkage causes the under-coating material to pull away from the metal, especially where the under-surface is slick.
A good example of the detrimental effects of undercoating is a ’69 Beetle which came from Ohio. When a friend showed me photographs of a car which he was contemplating buying, I noted that the car was from Ohio and encouraged him to check the undersides. After the purchase, I had opportunity to examine the car. I found it to be an original car, except for a fresh paint job. The engine never had been opened, etc. The car obviously had been undercoated “in the day”. But, oh, the rust on the bottom of that car! Moisture, dirt and salt had gotten beneath the coating and rust was rampant. “Cancer” rust! Such as rusted-through shock towers, etc., etc. The undercoating had hidden the oxidation all of those years and it had escaped cursory examination.
I discussed undercoatings with two qualified automotive restoration specialists. With one voice they agreed that no one who is restoring a vehicle should use undercoatings. That changes the nature of the car. To restore means to return to factory condition. Factories which manufactured Volkswagens never undercoated their cars. The cars were primed with rust-inhibitive coatings, then finish-coated. VW was proud of the rust prevention program which it practiced—it was an advertising gem in their crown.
We talked, also, about those of us who do not restore our cars but who recondition them nicely. Again, it was agreed that undercoating adds nothing to a car which, in most cases, never will be driven in conditions where it would be endangered by poor weather conditions and, especially, salted roadways.
These specialists also noted that nothing is gained by undercoating any vehicle. They both said that it was better to be able to monitor a car’s condition. Undercoatings make that virtually impossible.
Then, for cars which reside in dry climates, undercoating never should be considered.
I follow sales of VWs in order to stay abreast of the market. It is not unusual to read copy which touts new pan installation which has been undercoated. I have seen repaired pans under-coated in order to hide poor workmanship. Such coatings always are a red flag for me. Undercoating never should be used to cover new welds and seams. Proper smoothing, rust preparation and painting never should be circumvented.
Last, but certainly not least—undercoating is a nuisance when something on the bottom of the vehicle must be visited or repaired. And, even though there are “better” undercoatings available today (such as the now-famous bed-liners), all prove to be noisome to the mechanic or body repair shop when it comes to maintenance and repairs.
- Undercoatings never should be used when restoring a vehicle.
- Nothing substitutes for maintaining a clean vintage vehicle and avoiding conditions where the vehicle could suffer damage from weather-related causes.
- Undercoating adds nothing to the value of a vintage Volkswagen nor can it be proven to effectively protect the bottom-side of a vehicle.
- Undercoatings never should be used to hide poor workmanship or damage.