Most people wouldn't think of using ferrous sulfate to dye concrete. Typically used in plant fertilizer and medicine, ferrous sulfate will provide a distinct color on your concrete surfaces.
1 Use a putty knife to scrape away any imperfections in the concrete. Sweep the concrete to pick up loose dirt, dust and debris. Scrub the concrete with hot, soapy water and a stiff brush. Rinse with clean water and a mop, then allow the concrete to dry.
2 Tape off baseboards, door frames and any other areas you don't want to get the dye on with painter's tape. Lay plastic sheeting over any large fixtures in the room to keep them free from the dye.
3 Mix a solution of lukewarm water and ferrous sulfate into a large bucket, using a paint stirrer to combine the ingredients. The color you are trying to achieve will determine how much ferrous sulfate and water need to be mixed together. Use 16 oz. of ferrous sulfate for every gallon of water if you want an orange-colored dye. Mix 2 lbs. of ferrous sulfate, 2 cups of coffee grounds and 1 gallon of water for a darker dye.
4 Strain the mixture through cheesecloth held over a second bucket. Pour the mixture slowly onto the cheesecloth, straining any big chunks that have formed. Enlist a helper to assist you with this task.
5 Apply the ferrous sulfate dye to the concrete using a large rag. Dip the rag into the mixture, and then bunch it up to spread the dye evenly over the concrete. Work in 10-by-10 foot sections when applying the dye. Don't worry about getting the industry grade ferrous sulfate mixture onto the concrete perfectly; there isn't a right or wrong way to apply the dye. Use your own preferences and creativity as a basis for applying the dye to the concrete.
Therefore, ferrous sulfate can be also used to dye concrete.