Stained concrete adds visual appeal and interest to an otherwise drab building material. Although many commercial staining products are available, make your own custom stains. Acid-based stains rely on a chemical reaction to stain the concrete. Concrete will absorb stains at different rates, so make more stain as your project progresses. Add different metal, such as copper wire, to the acid instead of iron oxide, to get different colours, but the chemical reaction can take weeks and even months to complete. Regardless of the stain used, keep in mind that the age of the concrete and the amount of exposed aggregate will vary the appearance of the finished product.
Put on your rubber gloves and mask. Acid is a highly corrosive material and can cause burns to you or your work area if you spill it.
Measure the acid into a large container with a screw top lid.
Sprinkle the iron oxide over the acid. Do not mix it. The mixture will heat up due to the chemical reaction between the iron oxide and the acid.
Wait a few minutes. When the chemical reaction is complete, the stain is ready for use.
Dilute the stain with water until it is a light straw colour, this stain will result in a dark brown colour. Your colour preference for the finished product will guide the amount of water you choose to add. Do not use the stain at full strength.
Apply the stain to a test area of concrete to check the finished colour. Add more stain or water to your finished mixture until you get a colour you like. The more water you add, the more rust-coloured the stain will be. Keep in mind that the stain is often absorbed into the concrete at different rates giving a mottled appearance to the finished product.
Cover the mixture so the fumes do not corrode any nearby metal.
Record the ratio of stain to water used to achieve the colour you like so you can repeat the results as you work on your project.
Mix the iron sulphate and warm water together in a glass or plastic container using a non-metal spoon.
Mix until the powder is completely dissolved.
Use the stain immediately. If the stain sits unused for too long, the rust particles will separate from the solution and the stain will not work.
Avoid metal containers and spoons because they can interfere with the chemical reaction needed to make the stain.
Wash muratic acid off immediately with soap and water and seek medical attention if a burn occurs.