Mold and Mildew on Log Walls

//Mold and Mildew on Log Walls

Mold and Mildew on Log Walls

Mold and mildew on log wallsDoes Bleach Really Kill Mold and Mildew?

Bleach has been used for years as the “cure” for mold and mildew problems on logs.  However, some question

its effectiveness as a fungicide on porous surfaces.  Does it really get to the root of the problem?  Is it safe?  Does it hurt the wood it is intended to protect?  The answer is yes and no.

Is there a difference between mold and mildew?

First, it is important to understand that there is no difference between the terms “mold” and “mildew.”  These words are interchangeable, and either is correct.  From this point, we will be using the term “mold,” simply because that is the term more commonly used in the log home industry.

Why does mold grow?

Mold thrives when it finds a moisture source.  This could be because there is an existing leak close to the area in which mold has begun to grow, or because of constant exposure to nature.  In either case, when moisture is allowed to seep into a porous surface, such as logs and wood or concrete trim, mold will likely follow.

Simply removing the mold from these surfaces will only act as a “band-aid.”  It is important to determine the cause of the moisture, as well.  If there is a leak, fixing it quickly will be an important first step to eliminating your mold problem. Mold and mildew on log walls is a common area where moisture can accumulate, if not treated properly.

What can be used to kill and treat mold?

While bleach will kill surface mold, it will not get to the roots of the mold.  Bleach itself is mostly water.  Therefore, if you use bleach to kill the mold, you must make sure the treated area dries quickly, ideally within 24-48 hours.  Be sure to spray your cleaning solution from the bottom log to the top log, or you will have streaks which are almost impossible to remove.  Once the area has been cleaned and washed, and after the wood is dry, immediately stain the area.  This will seal the wood and prevent future mold issues.  Many stains now include a fungicide.  After many years of searching for better products, we now recommend Sikkens, an oil-based stain that will protect your logs for years, and is backed by a very good warranty and knowledgable people to help when needed.

What are some alternatives to bleach?

There are several EPA-registered products on the market today that can be used as an alternative to bleach.  Concrobium Mold Control contains no bleach or ammonia. It is best used for pre-treating building materials for mold resistance. Shockwave is a concentrated ammonium chloride cleaner and disinfectant, which can be used to sanitize and treat porous surfaces, such as logs and wood treatments.  Other products include Sporicidin Disinfectant Solution, Microban, and Fosters 40-80.  These three are mold remediation products, which absorb into the wood and penetrate to the roots of the mold.  All of these products can be purchased at your local home improvement stores and are relatively inexpensive.  Be sure to check which cleaner works best with your desired stain, as this can cause stains or paints to fail.

Mold is unfortunately a common issue on, and in some cases inside, homes of all types.  While all materials will exhibit mold if the proper conditions arise, it is important to treat your logs and exposed wood or concrete based trim with the proper materials.   Be sure to use good quality, kiln dried, or approved air dry logs to bring the moisture content down before treating.  Also important is the amount of time your home build is left open and susceptible to moisture.  Be sure to clean, dry, and stain before mold has the opportunity to become an issue.  If, however, the build takes longer, or your site conditions are prone to mold, there are many methods available to combat this problem.  For more information, please give us a call.  We would be happy to help you decide which process is right for removing any occurance of mold and mildew.

By |2016-11-30T11:59:55+00:00December 5th, 2013|Log Home Learning|66 Comments

About the Author:

Chris Sparks is an architectural designer specializing in residential log and timber homes. Practically growing up on job sites, he has been around construction and on sites since the age of seven (shhh! don't tell OSHA, it was okay back then). After graduating from the University of Tennessee, he began putting his construction knowledge and love of computers to use in the field of computer-aided design. Chris specializes in ArchiCAD. Chris lives in the Knoxville, TN area with his two children.


  1. Melissa Hall January 18, 2015 at 9:27 pm - Reply

    Hello, We recently purchased a log home that had been vacant for several years. Some of the interior walls have a mildew looking substance on them. It is whitish and spotty. What is the best way to clean this. I have used Murphy’s Oil Soap, but it came right back. Thanks for your time.

    • Chris Sparks January 20, 2015 at 12:14 pm - Reply

      Hi Melissa,

      Thanks for contacting us! The best way we have found to remove this type of growth is to use a 50/50 mix of bleach water. If it is on the outside of the home, a pump sprayer with the mix works well if used properly and in the correct direction. Shoot us over your email address and a few pics for reference and we can send more info, or get you in touch with one of our stain reps so you can ‘pick their brain.’ Give us a shout at [email protected] and we will hook you up.



      • Samantha April 30, 2016 at 5:49 pm - Reply

        I have the same problem. The cabin has been vacant for a few years. There are small white mold spots all over the inside bedroom walls. I’m a little grossed out! Bleach won’t hurt the wood? Would running a dehumidifier help?

        • Chris Sparks May 2, 2016 at 11:38 am - Reply

          Hi Samantha,

          Yes, running a dehumidifier will almost always improve the situation. The first step is getting rid of the moisture that is causing the problem. Running the HVAC while you are away should keep the problem from getting any worse, or coming back after cleaning. If you use bleach inside the home, make sure you follow the recommendations of the manufacturer and leave everything as open as possible to avoid contact with fumes. Best to contact a company familiar with the situation, but we have seen many people take care of the issue themselves. Let us know where you are and we can see about a company near you for a look.

          Thanks for contacting us!


          • Scott September 24, 2016 at 11:11 am

            Hi Chris
            We closed our cottage up, turned off the heat, and drained the pipes for the first time in years. The entire inside of the place is lined with cedar. This past spring we discovered white mold on the ceilings. We cleaned it all off with bleach…this did a nice job. What can we do to prevent this from coming back this winter? This past winter there were a lot of temperature fluctuations with the weather and the humidity in the place changed often because of this. A woodworker friend suggested we wipe all the walls down with bleach this Fall and also thought having a couple of fans running all winter to move air might help. Any other thoughts?
            Thanks, Scott

          • Chris Sparks November 28, 2016 at 10:10 am

            Hi Scott,

            If you are planning on keeping the HVAC off during a portion of the year, you will probably need to invest in a whole home dehumidifier with a permanent drain. This will keep the moisture content below 60%, as mold only grows over that mark. Might want to set it at 50 and see how it does.

      • Cam May 21, 2017 at 8:52 am - Reply

        Chris – I have a dresser that I have started to refinish. I had only painted the outside and stain to the top, before I started using it temporarily. However, I noticed an orange powdery mold on the inside of some of the drawers that I did not notice before I started. What would you recommend? Should I treat and then stain the inside of the drawers?

        • Chris Sparks May 30, 2017 at 11:26 am - Reply

          Hi Cam,

          Thanks for the email and the additional follow-up call. I hope we were able to help.

          Thanks again,


  2. Tanya January 5, 2016 at 10:15 pm - Reply

    Our issue is a tough one, the logs have “raw hide” sticky stain and are cedar. The issue is rotting wood beneath the stain. Turning wood black. The only thing that has worked is oven cleaner by previous owners. Grinders and sanders just gum up and strippers are extremely expensive, the wood logs are cedar so heavy grinding or blasting is not the way we want to go. Any thoughts anyone.?

    • Chris Sparks January 6, 2016 at 11:50 am - Reply

      Hi Tanya,

      Do you happen to know what type of stain is on there? It sounds like the chemicals may have compromised the structure of the topcoat.

      Generally, these types of stains can be removed with media blasting. While these stains are tougher to remove, if they are applied in the correct manner, they should last 6-10 years depending on the amount of weather and UV rays to which they are exposed.

      Could you send over a picture of the topcoat for us to take a look? Other than trying to figure out what type of stain is in need of removal, there are a few companies that specialize in this type of stain removal. The most important thing to do, besides the research you are already doing, is to test whichever method you choose on an inconspicuous area to be certain it is going to work as expected.

      Hope that helps some, but feel free to send over any pics or questions and we will do our best to help where we can.



      You may also try looking on the website. Many people voice their opinions on the best methods and practices in this area. Here is an example of a common page where you can begin looking into more info:

  3. Katy Quirrion January 8, 2016 at 4:23 pm - Reply

    So what is your suggestion to treat mold on logs that have polyurethane? They are very coated and shiny.

    • Chris Sparks January 8, 2016 at 4:54 pm - Reply

      Hi Katy,

      Assuming this is on the exterior of the home, the best way we have found is to clean them with 50/50 bleach or one of the cleaners listed above. Then wash them with clear water to remove the cleaner. Once the moisture content is back down to normal, then you are ready to recaulk and stain. Do you happen to know the brand of the stain used? There are several companies that specialize in this process. Let us know if we can help.



    • Chris Sparks February 18, 2016 at 11:08 am - Reply

      If the mold is on top of the treated logs, it should be as simple as testing a few cleaners in inconspicuous spots on the home and determining a best fit. There are several companies that specialize in this treatment, but we find a ton of people are more than capable of taking care of most of these situations. Please let us know if you need additional help. Will give it our best shot to help you come up with a suitable solution.

      Thanks again,


  4. cheryl February 14, 2016 at 7:00 pm - Reply

    I am interested in buying a log cabin house that was built in 1984 but theres dark stains in the bdrms in the corners & around the windows. Does this mean there`s mold in the walls? Is it possable to fix it & is it worth it?

    • Chris Sparks February 18, 2016 at 10:58 am - Reply

      Hi Cheryl,

      Could you send a few pictures of the areas? It is difficult to tell just by the description, but the most common issues we see in these area are typically mold. Unfortunately, without seeing them we are just guessing without more info. In homes with mold, assuming it is actually mold, we have found that pinpointing the source of the water is step one. It sounds like the home may have issues with stain or caulk failing due to time (given the age of the home). If this is the case, the fix is sometimes as simple as recaulking. Also, something to consider would be the HVAC in the home. These units not only control the temperature in the home, but also the humidity. Is the HVAC unit in use year round? If not, this could also cause moisture issues. Just let us know and, if possible, shoot over a few pics and we will try our best to help.



  5. Leslie June 5, 2016 at 12:46 am - Reply

    My frame house has log beams and cross beams and wood boards above that. There is widespread black mold. I’d be happy to send a picture that shows the problem.

    • Chris Sparks June 20, 2016 at 11:05 am - Reply

      Hi Leslie,

      Thanks for reaching out. I have emailed your personal address with more info. If you can give us a few pics we would be glad to take a look.

      Thanks again,


  6. Amy and Tom June 17, 2016 at 1:28 pm - Reply

    Hi Chris
    We live in Northeast Wisconsin. We have a log home that is 21 years old. 3 years ago we spent money on sand blasting our log home. After a lot of research and talk with various log home companies in the area, we decided to use Sikkens stain- Sikkens SRD, Natural light translucent wood finish. We were interested in having a lighter finish.

    We have mildew/mold (dark areas) all around various spots and we also have unsightly “drip marks”. No area on our home is shaded all day, but each area get about 4 hours of shade.

    We are so disheartened,angry and frustrated with the time and money we have spent and now at a loss to proceed with cleaning up the marks and mold.
    I can send pictures if you respond to our email.

    Any recommendations?

  7. Beth June 23, 2016 at 2:51 pm - Reply

    We have a log home that was black with mold and to clean it we use a 50/50 mixture of bleach and washed it off. As it has dried this week, there are apparent streaks from the bleach running down the walls. The walls were kept wet and we started at the bottom. This isn’t the first time we have cleaned our home and we haven’t had this problem before. We always re-apply Penofin stain. What can we do to get rid of the streaking? We can’t stain over this. It looks awful.

    • Chris Sparks June 23, 2016 at 3:45 pm - Reply

      Did you do the cleaning in the sun, or while there way shade? Did you keep the logs wet while you were cleaning on the upper portion? You should be able to bleach the wall again, while keeping it wet so it doesn’t dry out, scrub the logs to clean the bleach off once cleaned and you should be ok. Can you send a few pics of the problem? We can give more info after taking a look at what you have.

      • Chris Sparks June 23, 2016 at 4:48 pm - Reply

        Thanks for the pics, Beth. I have replied to your email directly with some comments.

        Thanks again,


  8. Robert Dreeszen June 24, 2016 at 11:54 am - Reply

    I am helping a friend/neighbor deal with the problems described above. The log home is 9 years old and located on a remote area of the Alaska Peninsula.The area is noted for its high winds and rain and we recently experienced a wind rain storm with 100 mph + winds that increased the problem we have been experiencing for several years with the moss/mildew described above. You offer several suggestions for the moss/mildew problem but I have concerns about how we can prevent future issues by dealing most importantly with the water entry from the exterior. My friend is shipping the most heavy duty exterior sealer he can find but my concern is how to deal with existing moisture currently in the logs. Because of the location we do not have access to most of the heavy duty drying mechanism’s and are open to any suggestions on how to deal with it . Will send photos and additional info to your email address. Appreciate any suggestions you might have.

    • Chris Sparks November 28, 2016 at 10:05 am - Reply

      Hi Robert,

      I have sent you a personal email on this. Was a bit long for the posts here. Hope the info helped.


  9. GENE GARLOCK July 13, 2016 at 11:43 am - Reply

    Chris, in the loft of our log home were getting mildew along the RIDGE BEAM and down two or three strips of the wood vaulted ceiling. We’ve been in the house for 15 years and this problem just started ? i was wondering if the ridge vents
    along the ridges need to be removed. With the way the vaulted roof is constructed with thick foam panels I always wondered what good the ridge vents did. WOULD APPRECIATE YOUR ASSESSMENT.

    • Dave Thomas March 29, 2017 at 8:08 pm - Reply


      This is our situation EXACTLY. I could have written this description myself. 20 years in our home, beam construction with T&G 2×6 yellow pine ceiling, ACFoam Nailbase on top of that, then metal roof. Mold growing on ridge or and down four courses of the T&G. We thought it was a leaking roof, but we also have moms on dry log interior walls. We are now running a dehumidifier in the winter, but why JUST NOW HAPPENING, after all these years?

      [email protected]

  10. GENE GARLOCK July 13, 2016 at 11:56 am - Reply

    Chris, Gene Garlock again. I forgot to mention that our air conditioner quit working and its only been recently that it hasn’t been constantly running. could it be that the moisture isn’t being drawn out of the air? having said that , the loft has never
    hah HVAC vents or been conditioned.

  11. GENE GARLOCK July 13, 2016 at 2:58 pm - Reply

    Chris, thanks foe getting back with the info. one additional question: is an attic fan useful in conjunction with a ridge vent system? or dose the ridge venting make the fan ineffective?

    • Chris Sparks November 28, 2016 at 10:01 am - Reply

      Hi Gene,

      The vent system would depend on the construction of the home. In a normal vented roof that we complete, it would have a ridge vent and a vent system inside the roof construction itself. If it is an attic area, then you would need a fan if the area is too “tight” and doesn’t have much venting.

  12. Moe Detmar August 4, 2016 at 4:14 pm - Reply

    Chris: I have a log home in southwest Idaho, built in 2007/2008, we coated the home with Sikkens Srd natural light in 2007 when finishing the framing of the cabin. We had a second coat applied in 2009, also Sikkens, natural light only this time it was the siding and log stain.
    As we prepared to stain this cabin again, we found severe mold exactly as shown on in your picture in this site. I have tried several chemicals to clean the logs, prior to staining, but each process does not seem to penetrate or remove all of the mold markings. I even have the beginnings of mold in my soffits and facia.
    The logs and siding boards are soft eastern pine and it concerns me to consider sand blasting to start over.
    Your thoughts, please

    • Chris Sparks November 28, 2016 at 10:06 am - Reply

      Hi Moe,

      Can you send a few pics up close? Sometimes the mold growth is under the layer of topcoat. This may happen if the logs aren’t cleaned and properly dried before reapplying the sealer.


  13. Becky Jensen September 5, 2016 at 10:23 am - Reply

    Hello I have a rustic little log screen house that really wasn’t taken care of. Has some rot and really dried out. I have sanded it, caulked the bigger cracks, and stained. But there is one side that has some blacks spots on the outside looks like mildew. Would you suggest to just sand it off or use a bleach solution before I caulk and stain that side. I don’t plan on spending big money just thought I would Dr it up a little and get some use out of it.

    • Chris Sparks November 28, 2016 at 10:04 am - Reply

      Hi Becky,

      We usually try to kill/stop the mold and let it dry before any sanding. This will help keep things from spreading in the sanding process. The most important part is resealing the area to not allow for air or moisture penetration. Without moisture mold will not grow, so use that to your advantage. Hope that helps, but if I am missing the mark shoot over a few pics of the areas and we will do our best to help.


  14. Mike Rizzo September 6, 2016 at 7:18 am - Reply

    Hi Chris! I have a 25 year old log home with a 20′ cathedral ceiling. At the top(roof) of the ceiling there is mildew/mold starting down the logs. Is this possibly rain blowing in my metal peak? How do I get rid of it and possibly stop it? Please email me. Thanks.


    • Chris Sparks November 28, 2016 at 10:08 am - Reply

      Hi Mike,

      Step one is ending the leak. It would probably be best to have a metal roof contractor to take a look and see where the water is coming inside the home. Once that is completed the mold can be treated with bleach or one of the cleaners listed in the article. After this it is crucial to reseal the areas to keep the moisture and air out to keep the mold from returning. If the stains are too heavy you can sand after bleaching and properly drying, then seal as usual.

  15. JKaren Barnrs September 27, 2016 at 10:43 am - Reply

    Hi Chris – Have a tongue and grove log cabin in northern Michigan. In areas the sun doesn’t melt the snow fast enough. We have some pretty bad areas of mold. In some areas, it’s 2-1/2 feet high. If we lived there, we could shovel the snow away from these areas.. It is a spring, summer and a few months in the fall cabin. In the past we used bleach, Bleach is part water. Would like to know a product to use – how to use it- and what kind a sealer to use. If I knew how to send pictures, I would. Please HELP

    • Chris Sparks November 28, 2016 at 10:11 am - Reply

      Hi Karen,

      I think I replied to this via email, but if I haven’t please let me know and we will do our best to help.

  16. Karen Barnes September 27, 2016 at 10:47 am - Reply

    Previous comment

  17. Lori Hilderbrant October 13, 2016 at 6:12 am - Reply

    What is the proper way to clean w bleach mixture. In sun or shade and i noticed the bottom to top and something about keeping it wet. Do u spray it on and let set for a few or immediately spray it off. Do u just spray one small area at a time w bleach or what

    • Chris Sparks December 2, 2016 at 4:27 pm - Reply

      You have to leave the bleach mixture on long enough for it to kill the active mold spores. The tricky part is not letting it dry in the middle of working with the wall. Only do as much as you can finish with rinsing to keep the bleach from filming up on the log. Sometimes you can’t cover areas and make shade, so the trick is to keep more water on the wall to ensure the area you are working with doesn’t dry before you finish. Hope that helps… If not, just let me know. There are some decent tutorials on youtube.

  18. Brian October 26, 2016 at 6:28 pm - Reply

    Hi Chris,
    I am having some mold problems on roundwood timber I am hoping you might be able to help with.

    Building is an octagonal structure, using roundwood timbers for the posts, beams, and rafters. We are located in the maritime Pacific Northwest. When I initially cut down the trees for this project, it was late spring. Soon after cutting them down, I used a draw knife to strip the bark, then left them in a part sun-part shade area to dry out sitting on some alder logs (as stickers). They were not rained on. In late summer we started seeing some black moldy growth on many of the logs. We washed all the logs with soap & water. They continued to get moldy. We tried treating them with white vinegar/water mixture & it did not seem to help. The only timbers that did not mold were ones where I stripped the bark later (brutal process where the bark & underlying wood had fused strongly together making the draw knife work very, very difficult; wood after stripping is very dry). The timbers that did mold were the ones that I stripped right away (draw knife more easily gets under the bark, exposing a very slick wood surface). Wood is doug fir & hemlock. Any ideas on what I can do to prevent this from happening in the first place?

    Thanks in advance for your time & help. Much appreciated.

    • Chris Sparks May 30, 2017 at 11:25 am - Reply

      Hi Brian,

      I sent an email on this one for some additional information. Please let me know if you didn’t get it.



  19. Karen November 11, 2016 at 10:08 pm - Reply

    I cleaned the interior walls of our log home with an oily orange spray furniture cleaner. They looked really great after cleaning because the wood looked so dry and was so dusty. One day later it appears the wood is a bit darker from the furniture spray. Did I mess up by using this? Someone told me this may increase the risk of mold.

    • Chris Sparks November 28, 2016 at 9:56 am - Reply

      Hi Karen,

      I sent you a personal email on this. Hopefully that will help.



      • Shirley Ernewin December 29, 2016 at 12:49 pm - Reply

        hi – I did the same thing with the oily orange spray furniture cleaner and got the same result with the darker wood. I wasn’t looking for darker wood, just hoped to help the dried out wood. Thanks.

  20. Fred November 28, 2016 at 8:12 am - Reply

    Hey Chris,

    I have mold forming on the ceiling in my home in a room that we mainly use for a storage room upstairs, I live in a log home.
    Would it be best if I scrub it by hand or am I able to just use a small sprayer with a cleaning mixture in it, and do I need to rinse with plain water after which ever way I do it?

    • Chris Sparks November 28, 2016 at 9:44 am - Reply

      Hi Fred,

      What material is the ceiling? Is it exposed timber or sheetrock, etc?



  21. Ginger Maltman December 1, 2016 at 4:24 pm - Reply

    Hi Chris – I am reading this thread with great interest. We have a 40 yr old home, but added an addition 25 years ago. The large upstairs bedroom is walled inside with pine t&g, floor to ceiling. We used penofin for stain, but nothing else over that. Over the past many years, I notice that there is a white “film” buildup, mold of some kind, on the walls. This is typically around windows and behind and near furniture pieces that are on or near the walls. I wipe it down with orange oil, but have never resorted to anything else. We are on the Oregon coast, so moisture in the air is certainly a factor. Only a cadet wall heater in the room (used rarely). Would you suggest the bleach/water for a good cleaning? Get a good dehumidifier? I am not opposed to adding a satin finish varnish/sealer of some kind once we get all the mold removed, but would that be reasonable to do, not really knowing what is actually causing it? We replaced windows in the room a couple of years ago, but don’t seem to notice much difference as far as the mold… my gut tells me it is simply excess humidity. If I were to add a varnish/sealer inside over the stained wood, how would I know when would be an appropriate time to do so? Thanks so much.

    • Chris Sparks December 2, 2016 at 10:21 am - Reply

      Hi Ginger,
      Sorry to hear you are having issues with mold in your home. It sounds like you have the right idea.

      Usually the perfect trifecta of defense in these situations is clean, dry and seal:
      1. Cleaning with a bleach water solution.
      2. Use a dehumidifier large enough to adequately dry the given square footage.
      3. Test for moisture content in the wood, if possible. If not, make sure you wait long enough for the dehumidifier to do the job. It never hurts to wait a little while longer if in doubt.
      4. Prepare the surface with a light abrasive. This should be recommended by your varnish supplier as it varies in more ways that many of us can imagine…
      5. Thoroughly clean all surfaces and even the carpets and ceilings, if possible.
      6. Seal the wood areas you are working with to help keep the old mold from growing again.
      7. Make sure the dehumidifier is set below 60% to keep that area from having any issues in the future. We recommend a little lower just to make sure.

      I takes some work, but mold is bad news and well worth the effort to remove.

      Hope that helps.

  22. Mark Dotson March 10, 2017 at 6:27 pm - Reply

    Hello Chris
    I have a 35 year old log cabin we built from loblolly pine. We have no water or electricity. I don’t have the ability to rinse the logs after cleaning with bleach. After cleaning I plan to spray Woodlife Copper Coat. Will not rinsing the logs after cleaning cause problems.
    Thank you
    PS great site for wood related info

    • Chris Sparks March 13, 2017 at 2:12 pm - Reply

      Hi Mark,

      Thanks for contacting us!

      Leaving bleach on the logs is possible without rinsing, but not recommended. The best way with that is to do small areas at a time with a hand sprayer on mist setting, then wipe that off with a sponge before it has a chance to dry. The important thing is to keep the areas small so you don’t get ahead of yourself too much and cause streaking in the logs.

      If you need any additional info, please don’t hesitate to ask.



  23. Dave Thomas March 29, 2017 at 8:14 pm - Reply

    Hi Chris,

    We thought our house was unusual, concerning mold on the INSIDE wood surfaces. See my response to Gene, several posts above. Are you getting more inquiries on this issue? We only have minwax stain on the interior surfaces, no sealers,etc. But why, after 15+years is this just now happening?

    • Chris Sparks May 30, 2017 at 11:35 am - Reply

      Hi Dave,

      Sorry for the delay. The conditions may have changed as far as the moisture content, the number of sunny days to combat the moisture, etc. Sometimes a leak letting just a little water in will be the reason that acts as a catalyst. Was the HVAC used and kept above 60 degrees all year? If not, that can cause issues if the home isn’t occupied for long periods of time.

      Hope that helps,


  24. anna levis April 29, 2017 at 3:49 am - Reply

    Mildew can be found on many different surfaces. It is a thin, black, or sometimes white, growth produced by mold. Molds are simple plants belonging to the group known as fungi. Though molds are always present in the air, those that cause mildew need moisture and certain temperatures to grow. They commonly develop in humid summer weather, especially in closed houses.These molds grow on anything from which they can get enough food. In homes they develop most often on cotton, linen, rayon, silk, wool, leather, wood and paper. Many synthetic fibers resist mildew.

  25. Cheryl Impagliatelli June 3, 2018 at 8:47 am - Reply

    Hi Chris,
    I have a small Cape Cod cottage in Truro, ma. It is close up for the winter. I noticed one of the small pine beams at the peak of the main room had some black spots. I just had a new roof put on last summer and there were no leaks. I also had a new ceiling with insulation put in the peaked ceiling. I cleaned it with bleach and was told to get a spray to prevent it from coming back. My concern is, could it be under the ceiling, can it grow on 1/4 inch insulation. Cape Cod had Terrible storms this past March and I wonder if that had something to do with it.

    • Chris Sparks June 4, 2018 at 3:34 pm - Reply

      Hi Cheryl,

      Most of the time, when a home is closed up with no air flow or circulation, the problem will show up eventually. It is recommended to keep a dehumidifier running if the HVAC isn’t on all the time. This will keep the moisture out of the air and keep mold from growing. You can plumb a full-time dehumidifier into a drain system to keep the moisture level down, or keep the HVAC on at a reasonable temperature so it will run when the conditions dictate. Hope that makes sense.



  26. Peggy July 3, 2018 at 8:16 pm - Reply

    Hi Chris,
    I have a log cabin in which a few of the logs have a green substance on it (algae?). I powerwashed it and most of it came off but there are a few areas that are still lightly green. Would you recommend using a 50/50 water/bleach solution on algae or just soap and water? Also, the cabin was coated with Penofin two years ago but I am thinking of using an oil based Cabot – do you have any thoughts on this?

    • Chris Sparks July 5, 2018 at 6:09 pm - Reply

      Hi Peggy,
      Thanks for reaching out. You could always use the bleach/water solution to clean the area, but make sure you follow the directions we have listed. As far as the stain goes, you may want to contact the company to find out if they have worked on an existing home under the same conditions. If you can’t get any info, please be sure to spot test it first in an area that doesn’t show as much. That should give you an indication of what to expect. Hope that helps, but if not shoot over an email and we will try to help the best we can.

  27. Deborah August 9, 2018 at 11:52 pm - Reply

    Hello Chris, we have white mold only on the inside large logs that run across the roof .Our HVAC is up in the loft laying on its side .We have lived in our log cabin for 30 yrs. but we are surrounded by tress and we have a Dam – water shed behind us. this has never happen before . We live in Maryland and we have had so much rain our roof on the out side is great, and the roof in side is good. We leave the temperature on 72 during the day and 67 at night. Do you have any ideas and is it toxin ? I would not want my family to get sick thank you so much for your help

    • Chris Sparks August 13, 2018 at 3:39 pm - Reply

      While we aren’t exactly mold experts, we have seen our share over the years. Could you send us some pictures of the area? That might help give us a better idea of what you have going on there. in the meantime, take a look here: Mold Facts for a fairly simple way to distinguish between mold and efflorescence. What you are doing with your HVAC system should be enough to combat mold in most situations, but sometimes water can come in from other areas, or not be properly disposed of through the condensation drain inside the HVAC unit. Let us know and we will do our best to help. Thanks, Chris

  28. Liz August 13, 2018 at 2:46 pm - Reply

    Hi Chris,

    Thanks for the post. I have a 20 year old cabin, purchased 4 years ago. I live in the finger lakes region of NY (very humid, also prone to abrupt temperature changes), and have a terrible condensation problem on the lofted ceiling of my cabin (wood paneling supported by log beams). It seems to be worst when temperatures are very high outside (i.e. air in cabin is cooler than air outside). I have a dehumidifier in the area that can control the situation most of the time, but its created a bit of a mold nightmare: because of the general humidity in the area, when these boards become saturated, it leads to mold proliferation all over the cabin. My questions: do you have an opinion about the best topical antifungal that can be applied to my cabin interiot? Is there anything I can take care of when resealing the exterior of the cabin (due to happen this year) that could help? Is there anything I can do in terms of insulation (currently have blown cellulose between my roof and ceiling)?

    • Chris Sparks August 13, 2018 at 3:33 pm - Reply

      It sounds like there may be penetrations from the exterior to go along with the condensation, but that is just a guess. For topical antifungal, the only thing not mentioned in the article would be a new product we are currently testing called RMR-86. We have just started testing this product, but so far it has worked very well. If there is any penetration of moisture coming from the roof, or even through the log walls themselves (this can sometimes be the case if the gasket materials were missed during construction) caulking any areas and then sealing with a product like Sikkens stain products will help keep the moisture out. If there is air penetration through these areas, along with your humidity levels, this can cause issues. With Sikkens, the last layer of the system acts as a membrane which will help keep air or moisture out of the interior. If the boards are becoming saturated, it sounds like it might be more than just condensation. You might get a pro in your area to do a leak test with smoke for air penetration. This may also be completed with thermal imaging, but that might be a little costly. To be honest, I am not entirely sure how much either of these would cost in your area. For insulation, what you have should be sufficient, assuming it was installed correctly. I hope that helps. let us know if we can help. Thanks again, Chris

  29. Wendell Nelson September 7, 2018 at 11:36 pm - Reply

    40 year old log home (log Pole Pine) – black mold on log ends primarily – clean off?? What can you tell me about RMR-86??

    • Chris Sparks October 2, 2018 at 11:29 am - Reply

      Hi Wendell,

      I may have already spoken with you via email, if so I apologize. We are still testing RMR-86 and so far, we have had positive results. I would recommend giving it a shot on a small area that isn’t easily seen first, just to make sure you do not have any issues with prior treatments or interactions with surfaces, etc. We are testing this now, and will update with any additional areas of concern. If you have any additional questions, please feel free to email and we will do our best to help.

      Thanks again,


  30. Peter Porter October 1, 2018 at 4:36 pm - Reply

    We just bought a log cabin in North Carolina that was built in 1993 and NEVER touched. It has 25′ ceilings and all of the above is grey with a mold. Down below you can use a vac and wire brush. If I hire a painter this winter, what should we do? Thanks, Peter

    • Chris Sparks October 2, 2018 at 11:26 am - Reply

      Hi Peter,
      Thanks for reaching out! And Aaah! Please hold off on the wire brush. Is this the plan for the log wall? If so, I would recommend another alternative. The wire brush would almost certainly mess up the surface of the wood. I would recommend using a cleaning agent like RMR-86. We haven’t been able to test the product long term yet as we recently discovered it, but the initial testing has yielded very positive results. If you would like, shoot over some pics to our main email and I can try to be of more help.
      Thanks again,

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