Unsealed concrete stains easily. You should be able to clean any stains or your surface will be unsightly in no time. You do not need expensive agents to do this, except for specific, tough stains. Most of the agents used to remove stains off concrete are commonly found in the house. Let's look at some of these common stains and their removal.
If your surface is stained by mildew and algae, you will need oxygenated bleach, hot water and a power washer. Oxygenated bleach is common in hardware stores. When mixed with water, it forms hydrogen peroxide which is very effective for clearing the mildew stain. Using the power washer, spray the moisture on the stain. The results will be immediate.
Another stain which is common especially in garage floors and driveways is oil and grease stains. If the oil is still fresh, it can be easily cleaned using dish soap. If the stain is tougher, you may have to repeat the procedure several times before it can clear. Wet the stain and pour some dish soap on the stain directly. Use enough soap to form lather. Then using a nylon scrub brush, scrub the stain thoroughly. After the stain has cleared, blot excess soap and water using an old towel. You can also use commercial products specifically for removing oil and grease from concrete. These work faster and do not require so much energy to use.
Rust is another common and unsightly type of stain. The best product to use on rust would be a commercial product specifically for removing rust. Oxalic acid works well. It is toxic and should be used with caution. Remember to wear protective gear when handling it. Mix the amount as specified in the instruction manual with water, dip your nylon scrub and scour the stained area. Let it sit for 10 to 15 minutes before rinsing off using plenty of water.