Advice | Why are red clay stains so stubborn, and how can I get rid of them?

Q: We live in a new community where houses are still going up and red clay is on all the streets. During last winter’s storms, we tracked snow mixed with the clay onto our concrete garage floor. Where snow on the underside of our car melted, we were left with red stains. Is there a way to remove the stains, ideally without having to clear out items we’ve stored in the garage? Should we put some sort of surface on the concrete to prevent stains from happening again?

A: You’re not alone in facing this problem. Red clay soils are very common in a large swath of the Southeast, with narrower bands in western Oregon and Washington and in part of California. Red clay soil — categorized as “Ultisol” in the U.S. Department of Agriculture’s grouping of 12 broad types of soil in the country — gets its color from oxidized iron, otherwise known as rust. Rust doesn’t dissolve in water, which makes red clay stains very difficult to remove. And clay particles are very tiny, so they easily find their way deep into porous surfaces, including fabric, concrete and other masonry materials.

Chlorine bleach, which is alkaline, won’t eject rust stains, so it’s useless against red clay. Some acids, which have the opposite chemistry, do remove rust and red clay. Products labeled specifically about clay often contain both acids and surfactants — soap-like ingredients that help eject the clay particles and keep them suspended until they’re rinsed away.

If you’re dealing with fabric, presoaking with detergent and perhaps an oxygen bleach is the key to getting rid of red clay. Websites for Tide and Clorox suggest a similar process: Use cold, running water to rinse away any clay you can’t brush off, presoak or treat with a stain remover, then wash.

For the presoaking, Tide’s website recommends submerging the item in water with some Tide detergent, or pouring the detergent at full strength onto the stain and waiting five minutes before adding the item to a load of wash with one to three Tide Oxi Pods, depending on the load size. Clorox recommends using a scoop of “good powdered detergent” in 2 gallons of hot water for a presoak of one to eight hours, rinsing and then pretreating the stain for 10 minutes with Clorox 2 For Colors Stain and Laundry Additive. Then, Clorox says, launder on the hottest setting with detergent and more of the additive, which contains hydrogen peroxide, an oxygen bleach.

Or you can pretreat with a product labeled for red-clay or rust removal, such as CLR Laundry Stain & Odor Remover (the new name for what was CLR Sports Stain Remover, $3.99 for a 22-ounce squirt bottle at Do it Best Hardware) or Iron Out Rust Stain Remover ($8.99 for a 28-ounce bottle at Ace Hardware). The Iron Out product is safe for whites but may remove dye from colored fabrics. (One caution: Make sure ventilation is good enough so you can avoid breathing the vapors after you add water, and avoid using this product entirely if you have respiratory issues or are sensitive to sulfite.)

Whatever cleaning products you use, air-dry the items, if possible, so you can repeat the process if you later notice stains you missed. Dryer heat can make stains permanent.

Sorting through options for the best way to remove red clay stains from concrete is trickier, in part because concrete mixes and finishing methods vary. Always test a small area, rinse well and wait until the next day to evaluate whether the cleaner has done any damage.

If you already own a rust remover, including one for fabric, try that first. If you need to buy one, look for a statement that it’s effective against red clay and read the application instructions to make sure they suit your situation. Some stain removers are labeled for exterior use only, which minimizes the risk of inhaling dangerous fumes where ventilation isn’t as good. Some products need rinsing with a power washer — a problem in a garage with lots of stored boxes. Other stain removers carry warnings not to use them on tinted concrete or on concrete that’s less than a year old. Many are designed for use on vertical surfaces where rinse water runs off, not on horizontal surfaces like garage floors, where the rinse water can puddle.

EaCoChem, which sells a range of cleaners to pros, markets its OneRestore cleaner for removing red clay stains and for general cleaning of concrete, glass, unpolished stone and brick. It works without scrubbing, but the cleaner is very acidic, so it’s critical to pay attention to safety issues.

Lynn Peden, owner of EaCoChem, said that for homeowner application, especially in a setting such as a garage floor, a more suitable product would be the company’s HD Britenol ($41.99 a gallon at Britenol is less acidic and works more slowly than OneRestore, Peden said, but the safety benefits are worth it. He suggested diluting it, mixing 10 parts of water to 1 part Britenol. “If that doesn’t work, go up to using it straight.” For a test area, he suggested measuring the ratio by capfuls. Even though this cleaner is milder than OneRestore, it still contains hydrochloric acid, and it’s critical to protect your skin and eyes and avoid wearing contact lenses when you use it.

First dampen (but don’t saturate) the concrete with water. Spritz on the cleaner with a spray bottle. “Squirting might be slow, but that’s better,” Peden said. It increases the dwell time, especially if you go back and spritz a second time a few minutes later. Work in small enough areas so the cleaner doesn’t dry before you rinse using a bucket of water and a mop. Dump the water wrung out from the mop into a laundry sink or other drain, even if your house is on a septic system, but don’t dump it into a storm drain or onto pavement that leads to a drain, Peden said.

CLR Calcium, Lime and Rust Remover is a more commonly available cleaner that works on rust stains ($6.99 for a 28-ounce bottle at Ace). A spokeswoman for Jelmar, which owns the CLR brand, said the company hasn’t tested the product on red clay stains specifically but has heard from customers that it works. She suggested diluting it half and half with water for a test and then for a larger area if the test shows no damage. Dampen the concrete, apply the cleaner, wait no more than two minutes, then scrub with a brush and rinse with cold water. Avoid using this product if the concrete is tinted, sealed or less than a year old.

If your garage floor is sealed, water should bead up, rather than sink into it. If it’s not sealed, applying a sealer should help prevent future stains. Make sure the concrete is clean and dry first. has a good how-to.

If you aren’t able to remove the stains completely, consider applying a red concrete stain to the floor, then sealing it. The blotches look ugly, but they’d be far less noticeable against a reddish background. And any future stains from red clay would probably blend in better.

Have a problem in your home? Send questions to Put “How To” in the subject line, tell us where you live and try to include a photo.

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