It doesn’t happen often, but certain colors of granite can rust. The image attached is an extreme example, but depending on the exposure, some granite (and other stone types) can rust when exposed to moisture.
I recently received a call from NY regarding a recent rust stain appearing on a grey granite. Granite being a natural stone is composed of many different minerals, and iron may be one of them. Untreated (non-resin sealed) granite is more likely to exhibit rust staining than resin-sealed granite. However, even resin-sealed slabs and tiles can rust if not properly protected using a quality stone impregnator.
Before you go to the hardware store and pick up a rust remover, you should understand that many rust removers are acid-based products, and it is vitally important that you test your ‘granite’ to make sure it will not be damaged by acid.
You may know that granite is a quartz and feldspar based stone and is acid-resistant, while marble, travertine, onyx and other stones may be largely calcium-based stone and acid-sensitive, and may be burned or etched.
Test in an inconspicuous area by applying the acid to the surface. If it immediately begins to fizz or bubble, you have an acid sensitive stone and you must remove the product immediately and flush with water. If the rust remover does not react with the stone, leave it sitting on the surface for 15 minutes, then wipe off, rinse and allow to dry. Observe if there is any noticeable change to the finish or color. If not, you may proceed to apply it directly to the rust stain. Follow the directions and dilution rate for your product and rinse.
Once the rust has been removed, it is important to immediately protect the area to prevent the rust from reappearing. When using acids, you are actually oxidizing the area and dissolving the rust. If not sealed, the freshly oxidized area will quickly rust again, and perhaps even worse than before. Sealing the stone (once clean and dry) will retard or even prevent rust from reoccurring. I suggest using a penetrating impregnator, not a topical sealer (acrylics).
HMK R77 Rust Remover is a Professional Grade Rust Remover for Natural Stone. Careful observance of directions is highly recommended.
R77 will remove rust stains from Granite, Bluestone, Fieldstone and other cast and natural stone surfaces. R77 may be used on both polished and textured stone. R77 is for acid resistant stone only.
Once area is clean, it is highly suggested that you treat the area with a quality stone sealer to prevent the return of rust.
HMK S31 is a Professional Grade Silane Impregnator. S31 is great for all natural stone but if your granite is in a kitchen application we suggest using HMK S34 Silicone Impregnator which has extra grease and oil protection properties for kitchen countertops.