What exactly is the Ziebart rust proofing material that the dealers used to spray in the rocker panels and cross members? It looks like a black tar material.....is that correct? Does it lose its effectiveness over time?

That's a name and product I haven't seen in many years. Not sure what the material is (was) but agree it seems to be tar-based or similar. It took many weeks for the smell to dissipate when applied. In the 70's and 80's living in the OH rust belt, Ziebart was well worth it based on our experiences.

As for holding up 30 or 40 years later, I haven't seen it more than 8-10 years old but was holding up well. Beyond wheel wells or other exposed areas underneath, I can't imagine it wearing or flaking.

Will be interesting to hear if others have better info

Kurt Ziebart sold his company and process decades ago, and bought a Mercedes dealership just out side of Traverse City, Mi., where I live. It was a secret mix, but did the job, as evidence by how nice your 914 looks! Lots of folks were puzzled by a Mercedes shop in the tiny berg of Acme, Mi., but I'm pretty sure he just liked living there, and had the sale proceeds to do what he liked.

I know it's not an infallable system, if you look closely in the window you can see this car was Zeibart protected.

That looks like it rusted from the outside in. There is no known cure for a case of dumb-ass! Leave a car out in the elements, it will decay

Ziebart must have worked on some cars in that condition....people are still buying them like that for big bucks!

My DD 1999 Honda was originally from Illinois and was Ziebarted. There is no Rust on the car and after it came to Florida, it lived 2 Blocks from Salt Water

Much of the success or failure was likely due to how well they could get access to inside of panels, and quality likely varied from technician to technician.

I recall in our area numerous competitors moved to a paraffin-based product as it supposedly flowed more than Ziebart thus covering better including dripping on the driveway for several days after application...

Drill lots of holes in the car. Spray the stuff every where. Terrible.

I probably stripped 50 lbs. off my '73 under the floor pans and in the wheel wells. 75% of the material was semi-soft and adhering to the paint really well. The rest was hard, flaking or cracking. That's where the real problems happen. Moisture and dirt gets up in the cracks and loose under-coating promoting corrosion. Add in the cracking seam sealer under the paint and you've got real rust problems. Also, the sound deadening material on the top side of the floor pans will do the same thing. Just think about 40 years of spilled Cokes getting under that and what that does to sheet metal.

If you read any of the British car magazines, for example Classics and Sportscars, you'll see Waxoil frequently mentioned as a rust protective for frames, underbodies, etc.

When I got my '71 I had it Ziebarted as it was going to be my DD for the for seeable future and IA LOVES salt. I was religious even in the winter to spray out the undercarriage at the quarter car washes (always fun in the winter when it was near zero) but yes they did drill a lot of holes! The stuff held up reasonably well through the 70's. Luckily after 4 years I got an old beetle as my DD.
Over the years I removed as much of the stuff as I could and the paint underneath held up pretty well.
They did my dad's 914 as well which he got 6 months after I got mine. Lots of holes as well, some in places they didn't need to do as it didn't even go into a closed place.

I have a hood in my shed that has this treatment. The fact that its Its rusting from the plugs out makes me laugh.

I've seen my share of hoods that have rust on the front edge by the latch. They put a water absorbing insulation in the inside for what reason don't know. With the water inside the insulation, it's only a matter of time before the rust comes thru.

Don't know if they put insulation in all the hoods or just later models.

Dave

While not exactly 914 related, I can say that my dad and I parted dozens of VWs (mostly Beetles) in the 1980s. The cars which had been Ziebarted were by far the worst of the cars we had dealt with. Surpassed only by one car ('67 Sunroof) that someone had rolled on latex house paint. That one car rusted from the outside in. These cars we parted were generally sold new in the rust belt to begin with and never left the area.

The Beetle may be unique in this topic as there were design decisions the factory made which introduced water to the heater channels and rocker areas once the seals started to shrink.

I think the Ziebart process could possibly save a car if it was taken care of and not abused by the weather. I would agree that if you leave a car out in the elements for a long time stuff happens.

A while back someone posted about a homemade mix that he applied to a piece of steel then tied it to a pier so it was in/out of the sea twice a day. No rust issues. IIRC, it was a mixture of some oil & wax that was sprayed on.

In theory probably not a bad thing for the rust belt vehicles..
But from many years of rebuilds and dismantling early 911 and 914...
It always seemed like the worst problem was the over zealous application of the material by the installer....ie more is better....thus plugging up the drain holes in the bottom of the doors and body panels....then there was the application holes themselves...apparently these were not prepped after drilling with rust preventive paint so it was just a bare metal hole with a nice plug in it but over time the plugs were removed, lost, and held moisture....you will find may of these with rust around the hole.
As mentioned it is a waxy/oily substance and not too much fun to deal with but can be removed.

My car has after market AC from the dealer. They sprayed this stuff all over the front trunk in and around the hole they cut. It did not keep the rest of my car from rusting though!

This sticker is on the back of my donor car that is sagging in the longs.