how to clean fiber cement siding on your homeEXOVATIONS is proud to be a James Hardie Preferred Remodeler. Along with installing beautiful siding, we also want to help you maintain your siding correctly. Fiber cement siding is designed to be extremely durable and need replacement less often than other siding materials. With that being said, it does require minimal upkeep to get the most of the product. With any type siding, prevention is always key to making it last for years to come.

(Not sure what kind of siding is on your home? See our blog post “How Can I Tell What Kind of Siding is On My Home?“)

So how and when should you clean fiber cement siding? The amount of maintenance needed will depend on the geographic location of your home. It is always recommended to clean your siding, as needed, to remove dirt, dust, mold, debris and build up that occurs over time.

Before completion of any siding repair or siding replacement project, EXOVATIONS removes any dust from the installation and construction process. From the beginning, you can expect to have a spectacular looking product when siding is installed by EXOVATIONS.

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As always, it is important to use appropriate safety apparel during cleaning. Always wear protective eyewear, gloves and respiratory protection. Depending on what debris is being cleaned from the siding, breathing in particles or debris coming in contact with your skin or eyes can be very dangerous. Always err on the side of caution when protecting yourself from dust, mold or mildew.

As well as protecting yourself during the cleaning process, be sure to cover any landscaping or plants. Using a thin poly or tarp will work fine. Just make sure your perennials and annuals are well protected from any spray or splatter of debris.

James Hardie recommends to first read any instructions outlined in your specific James Hardie product literature. After you’ve read up on the specific precautions to take with your product, it’s time to gather your tools. One of the most important things to remember is to never use a hard or abrasive brush. Using an abrasive scrub brush or sponge could damage the finish or siding.

Removing construction, cutting debris, dirt or chalk:
Recommended tools for removing any type of construction or cutting debris, dirt and chalk can be easily accomplished with an this method and with the following tools and solution.

  • Soft cloth,
  • Soft paint brush,
  • Chip brush,
  • Horsehair brush or
  • Siding brush
  • Water hose

In this case, we’ll only be using water as our solution to clean the siding. Simply brush the siding with the soft brush to free the surface of the culprit you’re trying to clean. Then, rinse with the garden hose. If using a soft cloth to remove the debris, with a wet cloth, wipe the siding clean and rinse with clean water. Change the cloth or rinse it often if there a lot of debris builds up on the rag.

Removing oil, grease or natural contaminants:
The recommended tools for removing any type of oil, grease or other non-chemical debris combined with a simple solution creates for an even simpler cleaning process. All you need is the following:

  • Soft cloth,
  • Water hose

We’ll be using a simple solution of a mild liquid dishwashing soap like Dawn®, Ivory® or Joy®. Just like you should never use an abrasive brush, never use any harsh chemicals to clean your siding. To clean your siding, wet your soft cloth with soapy water. Apply to the siding and use your water hose to rinse the area.

Removing mold and mildew:
The last contaminant you may need to remove from your siding is the dreaded mold and mildew. Mold and mildew thrive in moist, humid environments. Unfortunately your home will always be a target for mold and mildew. These similar fungi usually breed together so if you see one, you’ll more than likely see the other.

To tackle these fungi cousins, we’ll need the following tools:

  • Soft cloth or
  • Soft sponge,
  • Water hose

In this case, we’ll use something a little more pungent than water and liquid dish soap. Visit your local home improvement store and purchase a fiber cement siding safe mildew cleaner. James Hardie recommends using mildew cleaner like Jomax®, Mildew Check® or Mold Armor®. Mix the mildew cleaner with water as recommended on the mildew cleaner instructions. Strong mildew cleaners are often in concentrate form, so make sure to follow the directions correctly as not to damage your siding or yourself. It is extremely important to wear protective apparel when using chemicals and when in contact with mold or mildew. Lightly scrub the siding area covered with mildew with your sponge or cloth. After it’s sparkling and new again, rinse with the water hose.

Follow these recommended cleaning methods and the following pointers for any type debris removal. Always start work with small areas at a time and work your way from top to bottom. This will prevent streaking on already clean areas. When using your brush, cloth or sponge, always clean in the direction of the plank. Never allow the solution to dry on the siding; always keep the area wet with a water hose. If using a pressure washer, be aware high pressure water can damage the fiber cement. If you must use a pressure washer, always use a low pressure water spray with a wide tip, kept at a minimum of 6 feet from the siding and at a pressure under 1500 psi.

You can always ensure EXOVATIONS will do a fantastic job for your home. Contact us if you’re siding is beyond washing and you’re ready for new James Hardie fiber cement siding.

38 Thoughts on “How to Clean Fiber Cement Siding

  1. Joel Van Tassel on October 4, 2017 at 1:35 PM said:

    We just bought a 4 year old house that has Hardiboard. We heard the warranty is transferable. What do we need to do to get the siding in our name and how long is it warrantied?

    • ROONE UNGER on October 6, 2017 at 12:40 PM said:

      Joel – The warranty for hardiplank siding is 30 years. The details of the warranty can be found here.
      Based on the information, it does not appear you need to do anything to transfer the warranty. I hope this helps.

  2. Amy sangvai on September 20, 2017 at 8:18 AM said:

    1 coat of paint was sprayed on 2 of 3 sides of our Hardie Plank while it was still wet and partially dirty.
    I understand there may be issues with paint adherence when painting over a surface that was not fully prepared?
    Is there any safe way to remove that 1 layer of paint (solvent) and then start all over by properly cleaning, allowing time for it to sufficiently dry, and then painting?
    If not, we are left with cleaning what we can now and applying 2 coats of paint and waiting.
    If/ when we see paint failure such as blistering how is the paint then removed? Will it happen all at the same time?
    If reprinting areas are necessary will there be issues with color matching?
    I thought these kind of problems would be avoided using a reputable contractor but just as paint is only as good as the surface it’s applied to, contractors are only as good as the subs they use and supervise. In this case there was no supervision and the subs were even painting over trim that was raw, wet, not primed, and clearly had issues with rot in places. Thanks in advance, Amy

    • ROONE UNGER on September 24, 2017 at 9:43 AM said:

      Hello Amy –
      I reached out to the folks at James Hardie regarding your questions. Unfortunately as I suspected, there are no good ways to remove the paint without potentially damaging the board underneath. I would definitely not recommend solvents. Using a very High pressure spray to strip the paint also would run the risk of damaging the underlying board.

      If/when in the future it blisters/peels at the places where the dirt has been trapped, you should be able to remove any loose paint by brush or simply peeling it off or power wash. You should clean the affected areas, rinse and let dry before priming and painting. You would likely have to paint the entire wall to avoid color matching and gloss issues.

      I hope this answers your questions.

  3. John Douglas on August 16, 2017 at 2:52 PM said:


    We have had hail splatter all over the front and sides of our Hardi Plank siding and it has compromised the paint as it looks like I live in a speckeled house. The insurance company is telling us just to power wash the house and articles i have read said that can do more damage to the paint and siding?

  4. mary denzel on August 6, 2017 at 11:07 PM said:

    My hardie board siding (4′ X 8′ sheets) has weathered quite well for 17 years, but is showing signs of checking. How should I prepare it for painting over the original surface?

    • ROONE UNGER on August 7, 2017 at 9:36 AM said:

      Hello Mary –
      I have never seen hardie board “check” so I question whether you have the actual James Hardie product or another type of fiber cement siding. How you treat the checking board prior to painting depends on the width of the check. If it is under 1/4″, I would simply apply caulk. If the check is wider than 1/4″ then you could apply an all purpose bondo product and lightly sand after if dries to complete the finish. I hope this helps.

  5. Jamie Collins on July 22, 2017 at 6:06 PM said:

    Fiberboard siding/ cement siding.
    I hung a wire backed wreath and the wind blew the wreath back and forth and left marks in the siding. I have used soap and water and even some other cleaners and can’t remove the marks. Any suggestions?

    • ROONE UNGER on July 24, 2017 at 11:19 AM said:

      Hello Jamie-
      It sounds as if the surface of the paint has been compromised. In other words, you cleaned the siding but the paint has lost its color or has rubbed off by the wreath. I would recommend re-painting the area or the entire wall if necessary to avoid the potential for the new paint to stand out from the other areas. Painted surfaces, especially dark colors, will fade over time.

  6. Trena Radley on July 15, 2017 at 11:27 PM said:

    We have a burgundy color hardy board and have bat poop stains. White on burgundy stands out quite a bit. I’ve tried pressure washer and a scrub brush and a cloth all with Scott’s outdoor cleaner but nothing takes it away 🙁 what do you suggest?

    • ROONE UNGER on July 18, 2017 at 10:58 AM said:

      Hello Trena –
      It sounds as if the surface of the paint has been compromised. In other words, you cleaned the bat poop off but the paint has lost its color. I would recommend re-painting the stained/discolored area or the entire wall if necessary to avoid the potential for the new paint to stand out from the other areas. Painted surfaces, especially dark colors, will fade over time.

  7. Eryn on July 2, 2017 at 3:14 PM said:

    We have a BBQ that flared up and the smoke went up the siding wall, leaving soot mark. any thoughts on how to clean that? I tried Dawn and water and it cleaned up a little, but not completely. Should I use straight Dawn, leaving it on longer?


    • ROONE UNGER on July 3, 2017 at 9:00 AM said:

      Hello Eryn – I would try adding 1 part bleach to 10 parts water to the current Dawn mixture. Use a soft bristle brush to apply and scrub. It may take several applications to get it clean. If it will not come clean or get back to the original color, you can repaint the affected area. That may be the easier and quicker solution.

  8. Amanda on May 31, 2017 at 2:28 PM said:

    How do you remove eggs? Yes, we got egged. The joy of a corner lot on a busy street during senior week.

    • ROONE UNGER on June 1, 2017 at 9:56 AM said:

      Amanda – I’m sorry to hear about the egging. It could be worse. The cleaning instructions in the article should remove the egg. If you need to use anything stronger, it may remove the paint. However, it is difficult to damage the fiber cement siding itself. So worse case, you may have to repaint a few boards or possibly the entire wall. Depending on how old the painted surface is will determine how well the new paint color will match the aged paint color. I hope this helps.

  9. Stacey on May 25, 2017 at 4:48 PM said:

    How can you remove honeysuckle “suckers” from the siding without damaging it? We tore the honeysuckle down, but the suckers are very much attached to the concrete siding

    • ROONE UNGER on May 27, 2017 at 7:48 PM said:

      Hello Stacey – the instructions listed in this post are the manufacturers recommendations. Any cleaning solution or cleaning utensil stronger than what is stated may remove the paint. However, that may be your only option. Good luck.

  10. Kathryn on May 19, 2017 at 8:05 AM said:

    I decided to use pots in my window cages this year. I had the contractors who installed our James Hardie siding put them on so as not to nullify the warranty by doing it myself and perhaps doing it incorrectly. Last year one fell off almost hitting me in the head (luckly I was several feet away when it landed with a huge thump). The contractor came and put it back up. On the initial installment the worker had not placed in i the studs. But my question is this. I use the pvc fiberglass pot appropriate for the cages so they aren’t heavy…and I cleaned them with ‘wet tire’…what you use to clean the tires on your car…well…there were was so much water scale and ‘fading below the cages from 3 previous years and I had a microfiber cloth with a thin spray of ‘Armorall Wet Tire’…I thought I would wipe the boards under the boxes all the way down to the ground level where also mineral deposits were from watering the garden. Wow…really cleaned them up well. Also we have a split level home and the lower windows are at ground level and take a beating when it rains or I water or try to clean the ‘finish’ flashing that gets dirt in and on the separation between the planks and the flashing and the foundation. Is this a huge No No? It worked really well. I used it on the down spouts and they look great too. What is your ideas as to this form of ‘cleaning’ the water minerals from the lower part of the house? We live in an area where the water is extremely hard. Even washing my car it is a challenge. The water spots were horrible and I’m still trying to get rid of them from my windshield. We bought the Marven Prestige windows (not too pleased with them BTW) that were put in when the siding was put on and the lower windows around the house are all spotted. I have tried vinegar…windex…409…even glass stove top cleaner just on one because I wasn’t sure if that was appropriate or not. Could you advise me on this? Tire Wet or Maguire Cleaner/Protectant? is this just wrong? Hope to hear from you. Also would like instructions or advice on painting the exterior of one window. I called Marvin last year for this and never got the correct answer…they thought I was painting the inside….long story…no answer. A quote from a painter suggested by contractor who installed the Hardie board was 10,000 dollars…for one window….I don’t think so. I await the answers to these question if possible.

    • ROONE UNGER on June 1, 2017 at 10:09 AM said:

      Kathryn – I have never heard of using the “wet tire” products to clean hard water stains. I question whether is removed the stains or just temporarily covered them from being visually noticeable. If it works, I think using this on your fiber cement siding is not going to damage the siding, but could possibly damage or compromise the paint over time. I would not recommend using any of these products on your windows or glass. I think this would void your warranty. I have hard water in my area and the only product we have found to remove the deposits from glass is “Lime Away”. I would say it removes most of the stain, but if the build up is too great it doesn’t remove it all. Before using any products that are not recommended by Marvin on their windows, you should get confirmation that this will not void any warranties. I hope this helps.

  11. Paul Grice on May 17, 2017 at 8:52 PM said:

    We have a new home with hardy board siding, the siding has hard water stains from sprinklers that were set up by landscapers to water new sod. This issue affects every house in my new neighborhood. Any ideas how to remove these hard water stains? Thank you.

    • ROONE UNGER on May 18, 2017 at 2:39 PM said:

      Paul – That is a great question. I have the same issue at my home but have yet to do anything about it. So I did some research and talked with a few folks and here are the recommendations.

      Hard water has a high mineral content. When the minerals harden, the lingering stain is referred to as scale. Hard water scaling can occur on almost any surface, and it can be frustrating to clean due to the hardness of the minerals. You must use particular caution when trying to clean scale from painted surfaces because harsh chemicals can destroy a paint job.
      Using Vinegar
      1) Mix water and white vinegar in equal concentrations in a spray bottle. White vinegar is a weak acid, strong enough to dissolve hard-water scale but not strong enough to ruin a paint job. Because your problem pertains to hard-water stains, you may want to use distilled water in your mixture. Distilled water has very few minerals.
      2) Spray the water stain or stains directly and allow the vinegar to penetrate the scale. Wait about 10 to 15 minutes before proceeding, as the hard-water scale will take some time to soften.
      3) Wipe away the vinegar with a soft, damp cloth. If the hard-water stain begins to lift but refuses to disappear entirely, try spraying the scale again with full strength white vinegar. Wait another few minutes and wipe away the excess. If vinegar alone fails to do the trick, proceed to the next section.
      Using Baking Soda
      1) Mix a paste of baking soda using a concentration of about 3 parts baking soda and 1 part distilled water. Baking soda is another safe, natural product that softens hard-water scale without damaging paint. Add a few drops of white vinegar to your paste for even greater strength.
      2) Apply the baking soda paste to a sponge and gently scrub the hard-water scale. Allow the solution to penetrate the hard water for about 15 minutes before proceeding.
      3) Wipe the area with a damp sponge to rinse away the baking soda and hard-water remnants. Apply the solution a second time if necessary.
      Things You Will Need:
      Distilled water
      Spray bottle
      Soft cloths
      Baking soda

      Warning- Avoid using harsh chemicals like bleach and commercial limescale cleaners. While these may work wonders on metallic and unpainted surfaces, they can sometimes wreak havoc on painted surfaces.

      I hope this helps and please let us know how it goes!

  12. Sarah Cameron on May 14, 2017 at 2:43 PM said:

    Could you help us source a painter in our area, qualified to paint our James Hardie Fibre Cement siding . Closest towns are Owen Sound, Collingwood or Hanover Ontario

    • ROONE UNGER on May 17, 2017 at 10:05 AM said:

      Hello Sarah – I reached out to the folks at James Hardie for recommendations in your area. Here is the one company they referred us to.
      Spray-Net Guelph-Wellington
      (519) 968-3209
      RR # 2,
      Tottenham, ON L0G 1W0
      I wish you the best of luck with your project. Let us know how it turns out!

  13. Steve Vanaman on May 7, 2017 at 7:57 PM said:

    When hardie plank was installed the company used Henkel Corp Osi Quad Max Sealant 1868684. Its been 6 months and you can see where they wiped it on a few boards. it feels like putty, what can I use to wipe it off the boards. Thanks

    • ROONE UNGER on May 8, 2017 at 2:48 PM said:

      Hello Steve – here is my recommendation. I would use Goof Off to remove the caulk that was smeared on the board. Because the caulk was applied prior to painting, you will have to re-caulk and touch up the paint regardless of what you use to remove the caulk. Hopefully you wont have to paint the entire board or the entire wall so it looks proper.

  14. I have painted Hardie board siding on my house. Small black dots are sticking to the siding and I can’t remove it. I believe it’s artillery fungus. Is there any method to remove the fungus without damaging the painted surface? Thanks

    • ROONE UNGER on May 1, 2017 at 9:14 AM said:

      Hello Fred – Thank you for your question. Here are the recommended cleaning instructions from James Hardie. Using a low pressure water spray with a soft medium bristle (nonmetal) brush is most suitable for cleaning fiber cement products. If you are using a pressure washer, use wide fan tips that are kept a minimum of 6 feet from the wall and at pressures under 1500 psi. This will minimize the chance of damaging the siding. For stubborn dirt or stains, a mild detergent and a soft brush may be used. I hope this helps.

  15. I’ve got glue stuck to my white hardie siding from fly tape. I tried a stiff brush and dish soap, but was only to remove about 50% of he glue. Is it safe to use goo off?

    • ROONE UNGER on September 25, 2016 at 7:34 PM said:

      Hello Stuart –
      You can use Goof Off to remove the glue and it will not hurt or damage the siding. However, you may remove the paint depending on how hard you have to scrub which would require some touch up.

  16. Sandra Keown on January 3, 2016 at 3:31 PM said:


    How do I clean soot from a built-in grill that has blackened my hardie plank exterior wall? Thanks!

    • ROONE UNGER on January 4, 2016 at 10:07 AM said:

      Sandra that is a great question. I assume you have tried the detergent and water mixture with a brush as described in the article and that did not remove it. Unfortunately, the only way to remove the black discoloration is to paint it. I hope this helps.

  17. Good evening, I just stained my deck and got some overspray on my cement board siding. What’s the best way to remove these spots of stain?

    Thank you!


    • ROONE UNGER on December 14, 2015 at 9:52 AM said:

      Jeff –

      If it is an oil based stain, you will need to try lacquer thinner. Hopefully it will come off without too much scrubbing or it could begin to remove the paint from the siding. If it is a water based stain, you will just have to paint over the spots on the siding. I hope this helps.

  18. James DeCastro on October 6, 2015 at 10:22 PM said:

    “Before completion of any siding repair or siding replacement project, EXOVATIONS removes any dust from the installation and construction process.” How do you remove the dust from cutting the Hardie planks. Do you wipe with wet cloth, rinse with water hose, before nailing them up or do you do something after they are nailed up?

    • ROONE UNGER on October 7, 2015 at 11:06 AM said:

      James – Thank you for your question. During the siding installation process, we use special cutting tools to limit the amount of dust transmitted into the air due to regulations regarding Silica. After the siding installation, we pressure wash the home to remove any remaining dust and debris prior to applying the finish paint.

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