It cracks, then you add more, and it droops and sags, and you can't sand it without clogging sandpaper in the first few strokes, so you wire brush it, then it will NEVER be smooth, and you try to add more to seal and fill the cracks and gouges, but it droops and sags too, and it cracks again, and everywhere it cracks it allows corrosion and electrolysis, so when the substrate corrodes the Coal Tar epoxy starts to lose adhesion, then you need to wire brush or sand blast and start again because you can't sand the stuff.

Get the picture? I rarely use the word "hate" but I truly hate Coal Tar epoxy. (This is the voice of 8 years experience using it, like a bad addiction that causes cancer.)