Why use dangerous chemicals like acid to stain concrete when you can get beautiful results for less money without acid? Use iron sulfate (also known as copperas, iron sulphate, or ferrous sulfate) to stain your concrete a warm terracotta or rust color for a fraction of the economic and environmental cost of acid stain. Here's why and how.
Advantages of Iron Sulfate as Concrete Stain
There are many advantages to using iron sulfate as a concrete stain:
- Beautiful, natural colors and variations in shades
- No fumes
- Non-toxic, "green" characteristics
- Very low cost of the materials
- Very little time required
- Ease of use
A 15-pound bag of Hi-Yield Copper as Iron Sulfate costs about $15 and will stain approximately 1,600 square feet of concrete. If you prefer blue shades, use copper sulfate, both products are available at some garden, feed and hardware stores.
Prepare the Surface
Thoroughly sweep and clean the surface to which you'll apply the concrete stain. Use a mild cleaning solution such as Murphy's Soap. With a putty knife or other scraper, remove any surface grime or irregularities that you don't want to show on your finished project. Rinse with clear water and sweep the surface again. Carefully tape or drape plastic sheeting over any areas you don't want to stain.
Concrete Stain Recipe
1 Pound Iron Sulfate
1 Gallon Water
Combine ingredients in a non-metallic bucket or bowl using a wooden paint stick. Brush, spray (see note) or roll the mixture over the concrete. For spraying, save money by using the inexpensive lawn and garden pump handle types that cost about $10.
Mix only what you will apply within one hour since the colors fade after the solution has been prepared. For a darker, richer brown tone, add a pot of very strong coffee for every 3 gallons of the recipe.
Create Visual Interest
For variations in shades, allow some areas to puddle and dry (requires a longer drying time) or sprinkle the area with sawdust or other absorbent materials you have around the house. If your back permits, use crumpled newspaper or a sponge to dab the color off random areas.
For deeper colors, apply a second coat of stain after the first application has dried overnight.
If you want to get even more creative, crisscross the area with duct tape or create a grid or other design. Use duct tape to produce a firm seal so the stain won't run and ruin your design.
Spray or paint the area in thin coats with your iron sulfate solution and allow to dry. Repeat. Remove the tape as soon as the floor is dry to prevent the tape residue from adhering. The gray concrete will create interesting outlines for your "tile" floor.
Seal and Protect the Surface
Consider water-based, low- or zero-VOC (Volatile Organic Compound) concrete sealers, available in gloss or stain finishes. One gallon covers 300 to 400 square feet. Always read the manufacturer's guidelines. For example, to achieve a satin finish, some products require a coat of gloss to be applied first.
Note: To prevent clogging your sprayer, strain the solution through a cotton cloth.
For expert help with concrete installation or finishing, contact a professional concrete contractor.
Updated January 31, 2018.