Hi everyone, amateur DIYer here looking for a little advice. This is our neighbour's shed which backs onto our garden. I can only assume the previous owners here must have rendered it themselves as there is half a bag of now rock hard cement in our garden. Do I re-render or can the unlevelness be ground out? What is the best disc to use if so? As you can see I have attempted to grind it but it didn't do much. For context, I plan on painting it and making it into a massive chalkboard for my kids. Thanks in advance!