Redwoods are beautiful, shade-providing trees that can add drama and impact to your backyard landscape. They can drop a foliage and small limbs into your yard. Redwood also contains a high amount of tannin, which can stain your concrete patio a dark, unsightly color. If you are having problems with redwood staining your concrete, don't worry. With a few simple items and a little elbow grease you can remove those stains and restore the look of your patio.
Removing Tannins from a Concrete Patio
Hose down the patio. You can use a pressure nozzle in order to clean away any detritus or contamination that may be resting on the concrete surface.
Mix the wood brightener. I know it sounds strange to be using "wood brightener" on concrete, but what you are really looking for is the active ingredient "oxalic acid." Oxalic acid is a mild acid that neutralizes the tannins in redwood. Wood brightener is typically concentrated. Mix it according to the manufacturer's instructions.
Apply the brightener. You can use your nylon brush to spread the brightener over the concrete surface. Apply the brightener to wet concrete. This will help to keep the oxalic acid working. If the brightener is allowed to dry, it will become inert. Misting the concrete will reactivate the brightener.
Allow the brightener to sit for 15 to 30 minutes, then scrub the concrete thoroughly with your nylon brush.
Rinse the concrete. Hose it down with your pressure hose again. If the concrete is still dark, repeat the process. You can leave the brightener on longer if necessary.