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Welcome to the Bunnings Workshop community @tony84. It's sensational to have you join us, and many thanks for your question about sanding a concrete bench.
Can you provide a bit more information on the bench so our members are better informed and able to offer useful suggestions? Is this a homemade bench top that you've built, and could you provide us with some images? How much sanding is required? What type of finish are you going for? Is this going to be a highly-polished surface or just smooth?
Before you start, please have a look at the fact sheet on crystalline silica. Wearing a respirator when sanding concrete is extremely important, and wet-sanding is best to avoid airborne particles. If wet-sanding with electric devices, it's best to mist the surface so it's damp and not apply so much water that it becomes an electrical hazard.
Depending on the size of the area you need to sand, you can use an electric sander and standard oxide-based sanding sheets. If the surface is particularly rough to start with, you'll need to begin with a coarse 40-grit before moving through to finer grits. You'll chew through a few sanding sheets until it becomes smoother. Instead of or alongside sanding, you could experiment with using a cement skim coat to level the surface. Something like Dunlop 5kg Ardit Rapidset Repair Mortar could be suitable for this, especially if you're going for an ultra-smooth polished surface. The repair mortar will have a different texture and colour than the concrete, so you'll need to coat the entire bench.
Please let me know if you have any questions.
Mitchell
