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How to remove black fungus from window trim.

Post in 'DIY and General non-hearth advice' started by John_M, Nov 9, 2012.

  1. John_M

    John_M Minister of Fire

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    My window trims are coated with exterior Polyurethane over bare wood. Since installing energy efficient pleated shades, each morning after sub-freezing overnight temps, there is heavy moisture on the windows at the edges where the glass meets the trim. A quick wipe with a dedicated towel cleares the moisture but over the last two years or so, mold has grown where the window meets the trim.

    This mold does not occur on windows when the pleated shades are kept in the "up" position. So, I am going to keep the shades in the "up" position during winter months.

    I want to eliminate the stain and apply 3-5 coats of new Polyurethane for continued protection. The question is this: How do I eliminate the fungus which seems to have grown under the polyurethane and stained the wood? Bleach? Scrapng with razor, etc. ?

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  2. Backwoods Savage

    Backwoods Savage Minister of Fire

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    I'd try some white vinegar before scraping.
  3. semipro

    semipro Minister of Fire

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    There is anti fungal additive that you buy for paint. You can also buy bathroom paint that should already contain that additive.
  4. woodgeek

    woodgeek Minister of Fire

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    try reducing indoor humidity.....is your house 'tight' with no forced ventilation?
  5. nate379

    nate379 Guest

    Yup. Winter months you should keep it around 25-30%
  6. Highbeam

    Highbeam Minister of Fire

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    Still, you can get condensation on windows when it is cold enough outside. You can't stop the water. Bleach to kill the mold, it will come back eventually. Most mildew killing chemicals have bleach of some sort in them. Don't expect that your nice wood trim will always look new. That trim is in a pretty harsh location.
  7. John_M

    John_M Minister of Fire

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    Sorry about my temporary absence. Other issues have preoccupied my precious time.

    woodgeek, My house is tight with little humidity. However, I do keep a window near the woodstove open about 3/8" during winter months to allow a slight transfer of outside/inside air.

    Nate, Dry heat from the woodstove keeps inside air quite dry. I do not own a hygrometer but would estimate the indoor humidity to be less than 50%.

    I am able to eliminate evening condensation on windows by keeping the energy efficient shades "up" about 4". However, that 4" reduces energy efficiency of the shades. It appears I am in a "catch-22" situation; raising the shades eliminates condensation but reduces energy efficiency. Fully closing the shades increases energy efficiency but increases condensation.

    My next step is to keep the shades in the 4" "up" position to eliminate condensation. Will then attempt Dennis's suggestion to use white vinegar to clean the fungus areas. After cleaning, I will tape the window edges and gently sand the trim with "0000" steel wool. Will also determine if the anti-fungal additive suggested by semipro is available for semi-gloss polyurethane. Applying 3 or 4 coats of polyurethane is the final step.

    Thank you, all, for the suggestions. :)

    Best wishes and good luck.
  8. TradEddie

    TradEddie Minister of Fire

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    If this is happening overnight in rooms other than bedrooms/bathrooms, then you may have higher humidity than you think. Having a tight house means that interior humidity will increase in winter, because you are getting less of the very dry outside air coming in, and the humidity you generate by breathing, cooking etc stays inside. Conventional wisdom that a stove "dries out" the air is misleading, nothing about a stove can remove moisture from the air. (Stove heated air does have a lower Relative Humidity, and in the absence of OAK, stoves will draw dry outside air into the house).

    I expect that you are using shades to compensate for poor exterior windows, we have the same problem in our bedrooms, where the moisture we breathe out condenses on the cool glass. If your room air is at 70F and 40% RH, it will condense on any surface below about 40F, but reduce that humidity to 20% and it won't condense until the interior of the window is about 25F. To solve the problem, warm the windows, or dehumidify the air.

    Overnight, if you want to keep the heat in, there's not much you can do, but we find that opening the bottom of the shades just a few inches each morning will dry out the condensation very quickly, and drastically reduce the rate of mold formation.

    TE
  9. semipro

    semipro Minister of Fire

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    John, have you considered installing some shrink plastic on the windows to increase energy efficiency and decrease window contact with water?

    Gary, a member here has a great site with some info on doing this, even using removable frames which may work well for you.
    http://www.builditsolar.com/Projects/Conservation/conservation.htm#WindowTreatments
    midwestcoast likes this.
  10. heat seeker

    heat seeker Minister of Fire

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    Lack of air circulation encourages mold, so that's another reason that leaving the shades down helped the mold grow.
  11. midwestcoast

    midwestcoast Minister of Fire

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    If the mold really has gone through the poly & stained the wood it'll be a slow process. I'd first try to just clean with the poly in place without bleaching the wood tone. I'd try vinegar first as Sav suggests, or a vinegar & blue Dawn mixture applied warm or hot, if those don't work try an oxygen bleach like Oxy-clean (amazing stuff). If none of that works I'd assume you have to remove the poly. Personally I'd go with a good scraper. Chemical strippers for poly are pretty nasty & I'm averse. Sanding through poly takes a lot of time & sandpaper.
    Once finish is off try the above cleaners.
    Once the stains are gone I'd still give a quick spray with DILLUTED bleach to kill the mold & apply a new coat or 2 of poly.

    IF your windows are old single pane you could look at storm windows as a cheaper alternative to replacing. You can also get double pane glass retro-fitted into your wood windows if you're keeping them for architectural reasons.
  12. John_M

    John_M Minister of Fire

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    Thank you all for the suggestions. I have already started raising the shades about 4" each evening, hoping this will allow some air circulation and prevent condensation build-up on the bedroom windows.

    My home was built by me (and others) during 2004. The windows are the latest double glazed by Anderson with Argon gas between the glazings. They are quite energy efficient. The house envelope is tightly wrapped with Tyvek with taped seams. This is covered with 3/4" rigid board insulation with taped seams. All door and window opening gaps are properly insulated to prevent air intrusion.

    One can see in my signature below that an OAK feeds outside air to the stove. Also be aware that the upper half of a double-hung window behind the stove is kept open about 3/8" all winter. This small opening provides a little inside/outside transfer of air intended to prevent inside air stagnation. Cold outside air entering the house through this window is immediately heated by the woodstove.

    Perhaps temperatures this evening will be below freezing. If so, the 4" opening of the shades will test the air circulation theory of preventing condensation
    on the bedroom windows.

    The results of this test will be posted after a few nights of sub-freeqing temps. Once the condensation is eliminated I will repair the fungus issue.

    Happy Thanksgiving, good luck and best wishes to all. :)
  13. woodgeek

    woodgeek Minister of Fire

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    With all due respect it sounds like you have a great energy efficient house with a totally inadequate ventilation system. The science on this has come a long way since 2004. If the windows were single pane, sure, but condensation on the inside of good double panes is a classic warning sign. The simplest solution would be to upgrade a single bathroom vent to run at a low speed (20-40 cfm) all the time. A more energy eff and modern solution would be an HRV.

    I gather you crack the window b/c of other issues you noticed. The windows are telling you it is not enough. The cracked window is ok, but not really controlled. That is, a fixed crack might let in too little air (<20-40 cfm) during mild weather (as now), and too much during really cold weather, wasting energy.
  14. John_M

    John_M Minister of Fire

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    woodgeek posted: "...condensation on the inside of good double panes is a classic warning sign." Perhaps I wasn't clear enough in an earlier post: The condensation is not between the double panes, but on the bedroom side of the inside pane. The condensation is easily eliminated with a utility towel I have on hand for just that purpose.

    Regarding the slightly cracked window: I keep it that way +/- a teensy bit because it seems to allow easier breathing during winter months. My breathing is never difficult (have never smoked and do not have asthma) but that slight crack SEEMS to contribute to a feeling of overall wellness. I will be the first to admit the PERCEIVED benefit could be more mental than physical.

    My woodstove is located in the "great room" of the house. Two ceiling fans in that room run at their lowest speed 24/7 during winter months. It is all very comfortable. The only condensation "problem" I notice anywhere in the house is in the master bedroom. I believe you and others have suggested the proper solution: Allow some air movement to those three windows.

    A temporary "For what it is worth" comment: Outside temperatures here were in the high 20's last evening. Shades in the master bedroom were kept open about 2" and there was no condensation on the windows this morning. However, we all know a one time event does not a miracle make. I'll have to wait a few more days/weeks to determine if something as simple as opening a shade a few inches has solved the condensation problem.

    Good luck and best wishes to all. ;)
  15. TradEddie

    TradEddie Minister of Fire

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    I think woodgeek's point is that you would not be getting condensation on the inside of your windows if everything else was working correctly. If your windows are as efficient as you say, shades should not be needed. I think that the inside of even the most efficient windows would fall below the interior dewpoint if heavy shades block air circulation (the circulating air isn't really drying off the water, it's warming the glass above the dewpoint).

    Even if opening the shades slightly eliminates condensation, you might want to look into your house ventilation, if opening a window improves your air quality, this also suggests that overall ventilation is inadequate. You may have sealed that house up too much, you need fresh air, the ASHRAE requirement is 0.35 air changes per hour. This is necessary to reduce indoor pollutants, the carbon dioxide and humidity you breathe out, etc. This isn't some government bureaucracy thing, you need fresh air.

    One simple way to start would be to disconnect and temporarily seal that OAK inlet, if your stove doesn't draft well, you may be too tight, and the HRV suggested above might be a good idea. If it still drafts well, you are drawing fresh air into the house, that's good. Also, check your indoor humidity, opinions vary on what is considered 'good', but if living spaces are over 50%RH at 70F in winter, you're not getting enough fresh air. A closed bedroom is likely to be much higher than 50% overnight, but that can be improved by using doors with a larger air gap underneath, or louvers from room to room, or by leaving that door open.

    TE
  16. John_M

    John_M Minister of Fire

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    TradEddie, The compromise solution I will try is to keep the shades up 2" - 4" at night and run the bathroom fan located farthest from the open window near the woodstove for about ten minutes a few times each day. That will move outside air through the open window, draw it through much of the house, and exhaust it via the bathroom exhaust system. The conceptual solution is to transfer a limited amout of inside and outside air and keep the inside air moving. I use Vornado brand floor fans to circulate air during showers and they work very well. Except for occasional moments of needed privacy, all interior doors in the house are kept open 24 hours. With two ceiling fans, Vornado floor fans, and one bathroom fan, there should be enough circulation of inside air and perhaps an adequate amount of inside/outside air transfer.

    I do not want to get into the expense of a Heating Recovery Ventilation system or any other house modifications.

    Good luck and best wishes. :)
  17. heat seeker

    heat seeker Minister of Fire

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    I think that having the insulated shades covering the windows allows even the inside pane to get cold, argon not withstanding. Thus, any moisture will condense on the cold glass. Leaving the shades up a tad will allow some room air to warm the inside pane enough to prevent condensation.
  18. John_M

    John_M Minister of Fire

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    heat seeker, So far, my little experiment (shades about 2" up) last evening does prove your point. I will try the same experiment this evening and look for condenstion in the morning. After a week or so of these experiments I'll post the results for others to learn a little as I did.

    Best wishes and good luck.:)
  19. woodgeek

    woodgeek Minister of Fire

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    Yeah. I get it. Not condensation betwen the panes, but on the inside, when you have the insulated shades drawn.

    I personally think that the 0.35 ACH (forced) ASHRAE requirement is overkill (including cases like smokers, etc) and I would
    be comfortable with 0.2 ACH for house I lived in. I also think the payback on an HRV to provide that low of a cfm is not that
    great.

    Just saying that there are lots of folks in airsealed houses that just 'feel stuffy' or 'not well' in the house, and the only non-subjective
    thing that they mention is unexpected condensation inside windows. If you buy a cheapo hygrometer and the RH is 30% I'll drop
    the issue....if you're running 50% in january, I still think you have a problem.

    They make inexpensive timers that cycle bathroom fans on a small adjustable duty cycle for this purpose. It would be a cheap/easy retrofit.
  20. John_M

    John_M Minister of Fire

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    Update: There is no morning condensation on bedroom windows when I have the shades "up" all night. So, the condensation problem has been solved in the least expensive way. My next chore, perhaps during warm weather this spring, is to repair the staining on window trim caused by earlier fungus contamination. The recommendations of vinegar or bleach followed by light use of steel wool sound safest to me. Follow this with three coats of exterior polyurethane should bring all trim back to like-new condition.

    Thanks all for the helpful tips.

    Good luck and best wishes. :)
  21. heat seeker

    heat seeker Minister of Fire

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    And thanks for the update - I love to hear the end of a story!

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