Hi @julie14,
Welcome to the Bunnings Workshop community, it is fantastic to have you with us.
As long as there are no existing issues with moisture and the outside of the blocks is coated to prevent moisture transfer through them, then the process is fairly simple. If there is no water-resistant coating on the outside of the blocks or if there are any moisture issues, they must be addressed beforehand to prevent moisture from blistering the paint.
Assuming there are no issues, you should start by checking the wall for cracks, chips, or loose mortar and repairing any imperfections with a concrete patching compound. From what I can see, it is in fantastic condition and you should be ready to move on to the next step.
Once the surface is sound, clean it thoroughly to remove dust, dirt, or grease. A stiff brush like this Oates Long Handle Deck Scrub Brush combined with some Chemtech Brick Tile And Paver Cleaner, will do the trick. Allow the wall to dry completely before moving on.
You can then apply a coat of Dulux 1Step Prep Primer, Sealer & Undercoat, allow it to fully dry, then apply 2-3 coats of Dulux Wash and Wear Matt, tinted to something like Black Caviar.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
