Audi A4 2008 8K Underbody protection / Stone chip protection

Since newer cars have very little underbody protection/stone chip protection from the factory, I want to apply it myself. I once removed the fender liners, and there was nothing inside except for the primer coating.

What would you recommend I use? I've been looking at various products from Terroson, but there are so many different options for underbody protection/stone chip protection.

And how do I achieve that thick layer, like on the older models? I have a shotcrete gun.

I would not apply conventional underbody protection to areas hidden by trim parts, such as wheel arch liners. If preservation or personal preference dictates otherwise in those areas, I would use Mike Sanders cavity wax. The material is processed at high temperatures, exhibits long-term creep, and also shrinks into joints.

I would choose conventional underbody protection (based on bitumen or wax) for areas prone to stone chipping. Wax has a degree of "self-healing" properties when exposed to heat, meaning smaller stone chips can close up on their own. However, with wax-based underbody protection, you need to regularly inspect it and potentially reapply it. Compared to bitumen-based underbody protection, the advantage of wax is that you can easily see any changes to the bodywork (e.g., rust formation) and react sooner. While bitumen is more mechanically resistant, it can hide corrosion and other issues for quite some time.

I spoke with a VW mechanic/painter, and he told me that some Tourans have already been treated for rust formation on the underbody. That's why I'd like to apply a preventative corrosion protection, as there is currently no corrosion protection on the undercarriage of my Audi, even underneath the plastic covers.

Then remove the trim pieces, verschandeln them thoroughly, and let them dry. Once you've decided on the preservative to use, apply it, let it air dry, and then reattach the trim pieces. I wouldn't use any bitumen behind the trim pieces. Reasons are listed above...

Of course, after each winter, these covers should be removed again, and the winter grime (including any salt residue) should be washed off. After a visual inspection, it is then determined whether any further work is needed, or whether one can simply appreciate the good state of preservation of the conserved areas and take no further action.

@Hat Fahrer: If you properly seal a car component with bitumen, you won't experience any rust issues with a 2008 Audi. Otherwise, you are correct.

And how is the bitumen applied to achieve such a layer thickness? Is it applied by painting?

Hi,
I wouldn't use anything with bitumen in it; it becomes brittle and cracks over time. In the past, preservatives were made from PVC, which was almost permanently elastic. It likely resolved itself today due to the issue of disposal problems/take-back obligations.
I can only say good things about Permafilm based on my experience with my older cars. The product is relatively hard, making it suitable for areas prone to spraying, and it's essentially transparent; you can see through it. It also remains permanently elastic (at least, that's what 8 years of personal testing has shown). And if even Fiat body panels, which are almost four times older, don't corrode further, then the product must be quite good.

Best regards from Berlin,
olli

Is Permifilm more like a 'lacquer' or just a solid wax or something?

How to process?

Hi,
Permafilm is paintable, and likely sprayable, but it hardens slightly (becomes less sticky) and doesn't crack easily at higher outdoor temperatures.
Just Google it using the keywords "Fluidfilm" or "Permafilm".

Best regards from Berlin,
olli

I once inquired about a corrosion protection product called Permafilm for the undercarriage.

I received this response.

"For the underbody, either Fertan UBS220 (gold-brown, transparent) or Elaskon 2000ML (whitish, transparent) should be used. The idea behind using a product like Perma-Film is fundamentally correct, however, the quality and durability have noticeably decreased in recent times, making it more prone to becoming brittle." Of the two underbody protection waxes mentioned, one is clearly the better choice.