por-15 application question

I used Por-15 about 4 years ago under the hole body of my Scamp. Sand blasted, then treated it with the acid edging they give you. Then painted it with two coat as stated in the directions. The Por-15 is still on with no problems. I also treated a piece of sheet metal on both sides to teast it. I hit the piece of sheet metal with a ball peen hammer on both sides. The Por-15 never cracked or pelled off. Here is a picture, has dust on it from sand blasting other stuff.