How to remove a plant food stain on white granite?
Estimated Reading Time: 2 MinutesQ. Stain on white granite is plant food for flowers. Color of stain is blue. Have tried stone cleaner at least 3 time with no success.
A. Blue stains from water-soluble fertilizer can be surprisingly stubborn on light granite. The color usually comes from strong dyes and sometimes metal minerals in the fertilizer. These can soak into the stone, especially if the granite has a honed finish or if the spill sat for a while. Normal granite cleaner is not producing the results you want, because the staining agents have made their way into the porous surface of the stone. Here’s what you should try next.
Apply a poultice. For detailed, step-by-step instructions on how to mix and apply a poultice correctly, check out our free Stain Management App. A poultice will draw the stain out of the stone over time, especially if the stone is fairly new or if the granite is polished. Polished stone tends to keep the stain closer to the surface. The chemical ingredient for your poultice will be 30/40 volume hydrogen peroxide, available in a beauty supply store. Don't use the brown-bottle kind of peroxide. It isn't strong enough. Follow the manufacturer’s safety precautions.
Is the stain old? Has the staining agent penetrated more deeply because the top is honed or lightly textured? You may need to repeat the poultice method a few times.
Some fertilizers contain minerals like iron, zinc, or copper that can leave blue or green discoloration on stone. If the stain isn’t improving after a few rounds of hydrogen peroxide poultices, you can switch to a different approach by using a poultice made with an iron stain remover. This type of product is designed to target metal-based stains that peroxide may not lift.
Granite is generally resistant to acids, but for certain types of granite these products can cause dullness or an uneven appearance. It may be worth having a professional stone restoration contractor handle either the poultice work or schedule post-poultice services. To find a vetted PRO in your area, visit www.surfacecarepros.com and click on Find a PRO. They can restore the finish if the sealer is compromised or the surface loses its sheen.
ABOUT THE AUTHOR Fred Hueston is the Chief Technical Director at SurfaceCarePROS.com and Director at StoneForensics.com. He is also the author of Stone and Tile Restoration: The Manual, a comprehensive online manual for stone and tile restoration contractors. [Learn more about Fred.]