The blades usually work OK on thick coatings say 1/16th to 1/2inch. Trouble with rental equip. is that they cannot specialize too much so often one size fits all and those blades might not have been the right ones - definitely not.
Grinding is complicated. To remove a coating the diamonds should be coarse, say 30/40 grit or less, then they have to remain exposed from the matrix they are embedded into. To get this result the matrix bond should be soft enough for the concrete to wear it away to always keep new diamonds exposed. That means you have to grind down to the concrete while you are grinding the epoxy so the concrete will wear the matrix. To do that you push the grinder into the epoxy and back out again so that some of the wheel cuts the epoxy and some of it rubs across the concrete continually wearing away the epoxy and also using the concrete to wear away the matrix.
The photos show good "rocket trails" which means the diamonds are exposed and flattened diamonds where they are almost flat with the matrix.
You can get more information at
http://www.situp.com.au/Coating Removal.html
