I think your refering to FLEX additive , while I never use and never needed , as the new Uerathane Clears have pretty good elasticity, plus the Flex additive will change the color, look real close to factory bumper covers on all makes and models closely and you will see what I mean , they are usually a tad off, as the factories use flex additive. and they peal ....LOL

I have sprayed many of dually fenders glass and SMC plastic ( now days are made of SMC ) and have NEVER hade one peal or flake or crack, the only way it cracks is when a rock is thrown from the tire and will star it from underneath.

@74Dually,
You better check with a jobber what type of hardner you need for your color , I have no clue if what you have is compatiable with each other, they all have their own chemical make up and require the correct hardners to work .

You cannot put Acrylic Enamel Hardner into Synthetic Enamel color, or Acrylic Uerathane hardner in to the 2 I just mentioned.
Make darn sure you have what is compatiable with each other before you spray as you may have a BIG mess on your hands and may never dry or worse , turn to jello pudding when you mix the 2 together .


Spray