I had a contractor use Ardex resurfacing products to level my walkway. He did a horrible job at leveling the walkway and even worse is that there is a significant color difference in the concrete repair. I've contacted Ardex 3 times and they have not responded in any manner. I need to somehow seal the surface with a gray colored sealer. I'm VERY hesitant to use the Ardex sealer. What are my options?