Help With '97 F150 Undercoating

I'm doing some suspension work on the truck and nothing is working well on the undercoating removal. There is nothing on or in the truck to identify what the brand is but it's the best I've seen. No rust anywhere on the frame. The stuff has a texture like a pebble dashed stucco. Something was embedded in to the surface of the undercoating which I've never seen before but maybe someone here has and has dealt with this stuff. Sand blasting is a waste of time. A grinder works but it will take a minimum of 20 hours for what has to be removed. A torch gets it hot but does nothing to break through the surface. I've tried kerosene and fuel oil soaked rags wrapped around the frame with minor success but this will take more time than the grinder. If anyone has any thoughts or suggestions I'd appreciate hearing them. If it's any help the truck originally came out of the Philadelphia area.
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Had a feeling no one would respond but I did get help with this yesterday from a chemical engineering Prof. at OSU (OH). The advice was to think of the undercoating as something like paint. Paint has 3 different processes it goes through when applied, drying, hardening and curing and all 3 are controlled by the binders used. A lot more advice was given but briefly the removal advice was to break down the binders and the first suggestion to try something like WD-40 worked. This wouldn't have been the suggestion for an undercoating that didn't completely harden.
That's the rub, I don't know and it's why I asked. It's not my truck but usually there's a sticker inside the door and\or some maintenance and inspection literature in the glove box but there was nothing. Whatever it is, it's by far the best I've seen for rust prevention. Except for a spot about the size of a dollar bill on the top of the front cross member the frame so far from what I've seen is rust free. That's saying something for here in salt friendly Michigan. The Prof. that helped me speculated that it may not be something marketed as an undercoating but something the original owner had access to. To him it sounded like some of the coatings used in industrial storage tanks developed to protect the tanks from specific caustic materials they hold or maybe something used at sea. I sprayed the areas I needed cleaned every half hour to hour yesterday afternoon with WD-40 and then PB Blaster and hit it with a wire wheel on a grinder in the evening. It still took a couple of hours but it worked. If the stuff isn't sold as an undercoating it should be. It looks like the bumpy back on a gray toad but it works.

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