Q: Any idea what we should use to remove birch tree leaf stains from concrete? We’ve tried Simple Green and CLR. I’ve also seen suggestions to use bleach and water (in a 1 to 16 ratio) with a bit of dishwashing detergent. What’s the best approach?
To minimize stains, spread a tarp before having a load of wood chips delivered, and clean leaves as soon as possible, especially when there may be a string of damp days. Tannins are water-soluble, so dry leaves hang on to their tannins and don’t stain.
If a little staining occurs before you clear the leaves, the stains will probably be minor and go away on their own, especially if the concrete gets direct sunshine. The ultraviolet rays in sunshine bleach tannin stains quite effectively, but you can’t control the rate, and you might not even notice at first that they are getting lighter. The stains fade little by little; it can take an especially long time in a community where the sun angle is low and the sun is out for only a short time each day.
If you don’t want to wait, there are other options. Simple Green and other nonacidic degreasers are safe to use on concrete, and a solution of bleach and water also works on bare concrete. But bleach can strip color and damage sealer if the concrete is stained or sealed. Be even more cautious about using CLR, a cleaner with initials that stand for calcium, limescale and rust — mineral deposits that can form on many surfaces and that are often difficult to remove.
CLR is very acidic, so it powers through those deposits and breaks them down. But strong acids also break down concrete, so it’s best to avoid using acidic cleaners on concrete. This includes benign-sounding ones such as vinegar, even though you will find advice online suggesting it as a way to remove tannin stains from concrete.
Instead, try OxiClean (the basic product, labeled as versatile stain remover). It’s carried by most hardware stores and home centers. At Ace, a five-pound tub costs $15.99. OxiClean’s active ingredient is sodium percarbonate, a powder that, when mixed with water, releases hydrogen peroxide and soda ash. They are the actual cleaners, assisted by the bubbling action of the hydrogen peroxide.
OxiClean can be used on many surfaces, indoors and out. For removing tannin stains from concrete, first sweep the surface and hose it off. Getting the concrete uniformly damp before you add a cleaner is always a good idea, because doing so will yield more even results.
Although it’s possible to scatter OxiClean powder on wet concrete, then scrub with a stiff broom, it’s better (and easier) to first mix the powder with water. Use 4 scoops of powder per 1 gallon of warm to hot water. Mop that onto the concrete, then wait five to 30 minutes. During that time, you can scrub the concrete to make the cleaning more effective, but that is not essential. The solution shouldn’t dry on the surface before it’s time to rinse, so tackle a relatively small area at a time and add more of the solution as needed to keep the surface damp.
After 30 minutes — or before, if the stains appear to be gone — rinse with plenty of water. You can use a spray nozzle on a hose, but skip hauling out a power washer, because the pressure can erode concrete.
Runoff from OxiClean generally doesn’t damage lawns or decorative plants, although it kills moss and algae. If you accidentally dump a bucketful of the cleaning solution or a pile of the powder in one place, dilute the concentration by running a hose there for a bit.
Although pictures on some marketing videos for OxiClean show bare hands scrubbing it into stained fabric, wear protective gloves, and avoid getting any powder or cleaning solution in your eyes. The product’s website, oxiclean.com, says the pH, when diluted, can be up to 11. That makes it’s just about as alkaline as chlorine bleach, which ranges between 11 and 13. No smart homeowner skips putting on gloves to clean with a chlorine bleach solution, and it shouldn’t be any different with OxiClean.
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