Does your E9 have White undercoat?

Nicad

Nicad

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I thought that the undersides were painted body colour? Mine has a thin coat of Black undercoat mixed with dirt that scrapes off very easily with a wire brush and underneath is a very tough white undercoat. It is everywhere. Is this stuff factory original? I am just getting ready to remove it all and hoping I have the patience to see this through. So far in small test areas I find nice unrusted metal underneath most of the areas I have disturbed. Perhaps I should leave it? My eventual goal is to treat the bare metal with whatever paint system the experts suggest and recoat with body colour undercoat once I am sure there is no rust left behind.
Any tips from the Pros to help make my E9 a $110K 2002 greatly appreciated

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I would be inclined to leave it, except in areas where it is loose or rust is obvious. It is very difficult to remove - especially while on your back and working around all the suspension parts. Now that you have wire brushed it you may want to coat it with a rubberized undercoating. The undercoating is not typically body color.
 
I agree with Sven. Underside was never body color, it was a light tan color. It is pretty thick and oven cleaner will soak into it. I started to remove mine and stopped. We reapplied the factiry grey Wurth undercoating over the original paint. The grey turns black over time from soaking up oil and grease and road grime.
 
Nicad said:
That is impressive if it would cut through the White Stuff that easily. If I take it off, does anybody have a preferred long term corrosion inhibiting coating they can recommend?
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If it's not loose why would you want to take it off ? Believe me, if your car is rusting underneath the German rubberized undercoating you will see the undercoating bubbling and the undercoating will feel loose when you touch it. If the undercoating is still solidly attached to the metal underneath it has done its job and sealed out corrosive elements.

Personally, I would remove all loose undercoating, then clean up the bare metal and paint it with DuPont VariPrime. The needle–scaler that Don mentioned can also be used to remove rust when you hold it at about a 30° angle to the panel you are cleaning. Of course after the VariPrime has dried it should be undercoated, otherwise the sand thrown by the tires will chip it. ~ John Buchtenkirch
 
What's the desired result?

I, like many others wanted a "like-new" looking underside since I was putting that much work into the suspension and I had to take everything out anyhow.But I have to agree with John B. That stuff is stuck on there and it's brutal to remove. What I did was thoroughly wash the underside using a power washer, brushes, soap, grease cutter and then power wash it again and that revealed any loose coating which was scraped. It takes a long time and I have heard that the cheap air scrapers don't work that well on pliable coatings and in the tight spots, and that's where you need to get to most likely. You can spray some thinner on the greasy stuff, brush and wash again- then dry it with fans for a day or so and use compressed air to get in the tight spots- you'll want to rust-proof those crevices anyhow. After you apply primer, paint and new undercoating to the scraped parts what was suggested to me, and I did, was paint over the undercoating with black appliance paint-like you would paint a fridge with- that way it can be easily washed. Results attached- Tip: if you don't have a lift-see if you can borrow one for a weekend.
 

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Thanks for the Tips Guys. I guess I will leave the areas that are clearly solid alone and just scrape it down to the bare white undercoat, give it a solvent wash and recoat it with Grey rubberized sealer. Any seams however will have to come clean to insure that rust is dealt with completely. I basically don't trust undercoat. It has killed many a car in Canada when it dries out, water gets trapped underneath and rusting accelerates. I feel that working on an E9 is kinda like an artifact that you are doing your best to make it last longer than 1 lifespan. I do not have running water in my shop. I have a 50 gallon drum filled with water that I can use with a Campel Hausfield pressure sprayer for small stuff. On the White undercoat I did an experiment with Mastic Solvent used for dissolving flooring adhesive and it did work pretty well. I am very interested in getting a needle scaler now that I see what can be done with one. Looks indispensable for prepping rusty metal before welding. I expect this will take a while to complete. I still want to seam weld the floor like on the Coupeking website and perhaps add the Diff reinforcement plate while I am at it.
HAs anyone sprayed rust converter inside the hidden areas? There is surface rust under where my diff mount was. It is not serious, but it would be nice if it was slowed down. Once everything is done, the car will get a yearly soaking of Krown
http://www.krown.com/products/the-krown-product/the-krown-product/
 
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I used a product called Raptor. Buy the tintable stuff and tint to the desired tan color, then apply with a schutz gun.

I scraped off all loose undercote and treated the resulting bare spots with POR 15 before application.
 
Nicad said:
Thanks for the Tips Guys. I guess I will leave the areas that are clearly solid alone and just scrape it down to the bare white undercoat, give it a solvent wash and recoat it with Grey rubberized sealer. Any seams however will have to come clean to insure that rust is dealt with completely. I basically don't trust undercoat. It has killed many a car in Canada when it dries out, water gets trapped underneath and rusting accelerates. I feel that working on an E9 is kinda like an artifact that you are doing your best to make it last longer than 1 lifespan.
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Bob, your suspicions about undercoating are well-founded however it is a necessary evil. The undercoating minimizes sound carrying through sheet steel but more importantly it keeps the vapor barrier (some type of paint coating) from being sandblasted off the car’s sheet metal by sand thrown up from the tires. The undercoating is particularly important in the front wheel area because unfortunately our coupes don't have front fender skirts.

The tar based under coats dry up and crack over time. The capillary action holds water in the cracks and that that point the undercoating helps to rot out the car. The German rubberized undercoating is extremely tough and rarely ever cracks so I personally wouldn't scrape it off my car unless it was in poor condition. Unfortunately the downside is that it's so tough if water can get behind it, it becomes a bag that holds water against the sheet metal and rots it out. Usually seeing German undercoating bubbling is the first sign that the metal behind the bubble has some pinholes rusted through, the bubbling problems rarely start from the undercoating side of the metal. The bottom line is a coupe’s undercoating should be inspected often if the car is used in a lot of wet weather IMO. ~ John Buchtenkirch
 
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