Ironite is an acid-soluble metallic salt, which means that when it comes in contact with water or acid, it creates a liquid that imparts a permanent stain. Although this stain will not color everything and is not uniform in shade or transparency, it does provide a lovely mottled earthy brown stain to concrete. It is advisable that you perform a trial in an inconspicuous area to ensure that you actually appreciate the color it yields.
Ensure that the concrete is extremely clean and free of any debris. Wash the concrete area with a mixture of trisodium phosphate and water, mixed according to the manufacturer's directions, and scrub with a stiff broom. Rinse the concrete thoroughly with water to remove all traces of the cleaner.
Broadcast handfuls of ironite across the concrete surface. You can use a systematic or a random approach, but keep in mind that each place a granule of ironite lands will be colored a deep, earthy brown. Small puddles of water standing on the concrete will disperse the ironite, causing a lighter shade of stain. Allow the concrete to dry thoroughly.
Repeat the above process if the stain is not dark enough or if you want a more uniform color. Each subsequent layer of stain will darken the surface of the concrete. Make sure you allow the concrete to dry for at least six hours between applications of water and ironite.
Dissolve 1 lb. of baking soda in 5 gallons of warm water the day after you apply the ironite. Rinse the stained concrete area with the baking soda solution to remove excess stain. The baking soda solution halts the staining process so that the surface will not fade with exposure to water or rain.