Removing And Preventing Two Common Cedar Siding Stains

Posted on: 9 December 2015


If you have siding adhered to your home that is made out of cedar materials, then your home likely has a warm red appearance on the exterior. Cedar is a strong and resilient wood that is likely to remain beautiful for many years. However, you may see some stains appearing on the exterior of your siding over time. Most stains can be removed with a little elbow grease and the right cleaning solution. Keep reading to learn about some common cedar siding stains, how they can be removed, and how they can be prevented in the future.

Discoloration From Extractive Bleeding 

Cleaning Stains

Woods contain a variety of natural organic compounds called tannins that give trees their color. Most tannins are yellow or brown in color and they typically remain in the wood for some time. The tannins will leach out of the wood tissues eventually and you will see that your siding starts to appear more weathered or gray in color when this happens. Tannins can also be washed out of the siding if it is exposed to a great deal of moisture, and this is likely to cause dark brown blotches to appear on the siding. The stains are called extractive bleeding stains and they can be removed with a strong acid called oxalic acid. Look for a cleaner that contains this acid, like a product that is labeled as a wood bleach.

Since the cleaner is incredibly strong, you should make sure to purchase the appropriate gear to protect yourself. Long rubber gloves and some goggles will work well for this job. When you are ready, place about one and a half to two cups of the powder cleaning material in a bucket with one gallon of hot water. Use a rag or a scrub brush to apply the solution to the stains and watch them closely. Once the stains fade and appear close to the color of the unstained siding, rinse the acid with clean water from a hose. Allow the stream of water to flush the siding for about 5 to 10 minutes to make sure none of the acidic solution remains.

Preventing New Stains

Once you have removed the stains from the siding, look for a possible cause of the staining. The presence of a consistent moisture source will cause the stains to appear, so look for gutter leaks or missing downspouts that may cause water to cascade down the siding. Also, loose flashing may cause a moisture issue too. Leaking vents, as well as the presence of ground moisture absorbed by the siding, can be the source of the moisture as well. Once you find the source of the water, make necessary repairs or contact a contractor who can fix the areas for you. 

Iron Discoloration

Cleaning Stains

In some cases, you may see either reddish brown or blue and black stains appearing on the surface of your cedar siding planks. Both of these stains are caused by the oxidation of iron nails. Reddish stains are ones seen when the oxidation seeps into the top layer of the wood, and the blue stains are noted as the rust mixes with the wood tannins. These types of discoloration are usually seen in older homes where wrought iron nails were used on the siding. The stains can be removed with trisodium phosphate. Trisodium phosphate can be found at your local home store. 

Mix about one cup of the trisodium phosphate with two gallons of water in a bucket. The cleaning material is a strong base, so make sure to wear rubber gloves and a pair of goggles. Dip a scrub brush in the solution and lightly scrub at the stains. Leave the cleaning material on the stain afterward for about 10 minutes and rinse it away. You can repeat the process if the stain still remains. If the discoloration appears to be faded, then wait until the siding has dried and use a piece of fine grit sandpaper to get rid of the remaining oxidation.

Preventing New Stains

The only way to truly prevent new stains is to have old wrought iron nails replaced with galvanized aluminum or stainless steel varieties. If stains continually appear in the same areas across the cedar, then think about asking your siding professional to replace nails in these areas. You can also inspect your siding weekly to remove oxidation before stains have an opportunity to seep into the wood. Whenever you see a reddish brown or blue stain, use dish soap and water to clean the area immediately.