So if you want the coating to stick to the concrete it has to be at least a little rough. If you have not acid etched the concrete yet, then you are in luck. The chances are that when you do acid etch, the calcium sulphate will be removed from the surface and leave you with a more porous surface, which in essence equates to being more rough.
However, there are times that even after a good etching, the surface is still too smooth. If this is the case, you will probably be stuck with either sandblasting or grinding the concrete to get it into shape.
If you are going to sandblast, be sure to choose a quality professional to do the job. Sandblasting can make a mess and the last thing you need to worry about is the guy doing the job and whether or not he does that without making a serious mess or damaging surround items.
If you prefer to grind, then an angle grinder equipped with a flexible sanding disk that is about 36 or slightly finer will do the job as well. Make sure you wear proper protective clothing as flying debris can damage your eyes.
Once all has been blasted or ground down, you will have to acid etch again, as the newly acquired surface will have fresh calcium sulphate in it that will need to be removed.