Do you know anything about the undercoating that Fiat sprayed inside wheel wells during manufacture?

I recently sprayed over some with hardware-store-brand undercoating. The new undercoating has cured as expected where sprayed on primed metal. But where sprayed over this OEM substance, the new product is not curing. After several weeks, it is tacky and comes off on your hand if you touch it.

I know there are undercoating products that stay tacky. The one I used is not one of those. It has dried like paint everywhere except on top of the original product.

I don't have a good answer for you. It seems like after several weeks that the solvent "carrier" in your spray undercoating should have evaporated, but it seems like your new coating is reacting with the original undercoating and not curing. Perhaps after a long while, and especially with some road dust getting up in there, it would eventually dry. Still, I'm not getting a warm fuzzy feeling that this is happening in your case.

Sorry to not be of more help...

-Bryan

The old coating to me appears like more of a coal tar base than a cured coating so any paint over coal tar is not going to cure very quickly if at all.