What is the best way to paint over old concrete?

Clean Off Concrete. Use a stiff-bristle brush to remove loose concrete or debris from trouble spots. Patch Holes and Cracks. Patch small holes or cracks using a putty knife and concrete compound. Sand Smooth. Sand off any rough spots or bumps. Prep Concrete for Paint. Prime and Paint.

Firstly remove any loose material, or as much as possible. Fill small cracks with an exterior filler, large defects with a mortar mix. Once you're happy with the surface and it's reasonably dust free you'll need to prime it. I personally would use Zinsser Peel Stop, once it has had a couple of coat you can cover it with most paints. Hope that's helpful. Mark

Clean the surface: Before painting, make sure the concrete is clean and free of debris, oil, and other contaminants. Sweep the surface thoroughly, and use a pressure washer or a scrub brush to remove any stubborn dirt or stains. Allow the concrete to dry completely before moving on to the next step. Repair any cracks or damage: If the concrete has cracks or other damage, it's important to repair them before painting. Use a concrete patching compound to fill in any cracks or holes, and allow the compound to dry completely before proceeding. Etch the surface: Etching the surface of the concrete with an acid solution can help to roughen it up and create a better surface for the paint to adhere to. You can buy a commercial etching solution at a hardware or home improvement store, or you can make your own by mixing water and muriatic acid according to the manufacturer's instructions. Be sure to wear protective gloves and eyewear when working with acid. Prime the surface: After etching, apply a coat of concrete primer to the surface using a roller or brush. The primer will help the paint adhere better and last longer. Allow the primer to dry completely before painting. Paint the surface: Finally, apply your chosen paint to the surface using a roller or brush. You may need to apply more than one coat, depending on the coverage and color you're aiming for. Allow each coat to dry completely before applying the next one.

The first part I can agree with however using a concrete compound this will shrink and crack again, what you should use is a product called tupre I think I think I have spelt it correctly when it drys it can be sanded like sandstone. Hope this helps you can buy it from crown paints or Brewers.