Hi @Lifer,
Welcome to the Bunnings Workshop community, it is fantastic to have you with us.
Firstly, do you have any photos of the garage floor that you can share? Let me know if you need a hand uploading photos, I would be happy to help if required.
I imagine the stains are things like engine oil, dirt, maybe paint? Would that be correct?
Does your garage floor have any kind of seal on it? A concrete sealer, or perhaps epoxy paint?
Any additional information you can provide would certainly help.
With any concrete cleaning, a good pressure clean is a great starting point. Pressurised water can lift a lot of the easier stuff, like dirt and sediment, out of the concrete.
Combining a pressure clean with a degreaser or concrete cleaning product such as this Gerni Concrete And Stone Cleaner or this Chemtech Concrete And Driveway Cleaner can also help with tougher stains.
For stains that are really in there, a concrete etching product, like this Rust-Oleum Concrete And Garage Clean And Etch would be the way to go.
If none of these products work, the strongest option is to have the surface ground back with something like this Floor Grinder, to remove the upper layer of the concrete and any stains that sit in it.
I imagine one of these methods would prove useful to you, but I'd be happy to assist further if there were specific conditions that were outside of what I've described.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
