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Black Mildew on white wood


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We have a recurring problem, after treatment (JoMax, bleach) and even fresh paint, with a black mildew that shows up on the side of our house every year (some years better/worse than others).Oddly, the sunniest side gets the most... it IS the side that faces a river, about three blocks away. Cleaning it every year is crazy, and almost has us thinking about siding (Hardi Plank maybe?). It's a 3 story house, 1800s, wood... New England. We don't notice it so much on other houses but many of them are vinyl sided.

Any suggestions? Is this just something that happens? Thanks!

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Hey LorLee,

Welcome to the board. It would be quite helpful if you have a photo of the affected area. A "long" establishing shot and a close one.

There could be dozens of answers and solutions, so photos are good!

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Hey LorLee,

Welcome to the board. It would be quite helpful if you have a photo of the affected area. A "long" establishing shot and a close one.

There could be dozens of answers and solutions, so photos are good!

Thank you! Here are two photos, and the close-up photo shows clearly where we stopped cleaning one wall last year... over the winter/early spring, the clapboards we didn't bleach clean got pretty dark in this particular spot.

We need to pay somebody to get up high on these ladders and clean... I really don't want my husband doing it year after year. It's driving us crazy. ! (NO mildew or mold issues inside the house.)

Thanks for any ideas....

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We have a recurring problem, after treatment (JoMax, bleach) and even fresh paint, with a black mildew that shows up on the side of our house every year (some years better/worse than others).Oddly, the sunniest side gets the most... it IS the side that faces a river, about three blocks away. Cleaning it every year is crazy, and almost has us thinking about siding (Hardi Plank maybe?). It's a 3 story house, 1800s, wood... New England. We don't notice it so much on other houses but many of them are vinyl sided.

Any suggestions? Is this just something that happens? Thanks!

Back in about 1990 or so, the government told paint/stain manufacturers that if they put a mildewcide in their exterior paint or stain, they had to start jumping through a gazillion EPA hoops not present prior to that time. So, the manufacturers simply quit putting the mildewcide in their products. What you're seeing is a result of that.

Oddly enough, the paint stores were still allowed to sell packets of mildewcide right next to the new-formula paint/stain; all the customer had to do was pour it in the paint/stain. I suspect that's why you say the staining recurs even after re-painting; no mildewcide in the paint/stain you used.

The *mildew* on the house is feeding off organics in the paint/stain; you need to apply a mildewcide.

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Wow, thanks! We painted about ... 4-5 years ago. Then noticed the mildew coming back each year, in different places (patches).... the painter INSISTED he put mildewcide in the paint. Maybe he forgot? He was... not the most um... top of the line painter around here, we think.

We cleaned last year and the year before, with JoMax ... and the places where it's coming back are both in some of those spots and in new spots.

We are in need of paint in some places and thought maybe we'd hire a top notch painter, to scrape all the way down, "treat" the wood (and I have no idea what that means but it sounds good), apply primer and paint with mildewcide mixed in. Is it possible that could take care of the problem? We hate to pay for paint where we only need cleaning, and was thinking of asking the painter if he'd do that, once they're up on scaffold or ladders. ?

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LorLee,

It is painful, but Jerry and Scott likely are correct!

I am a great believer in good paint and good painters. I certainly can't see the entire job from your photos, but what I see looks a little on the skimpy side.

The solution now would be; scrape, prime and repaint with the good stuff. I don't know of any magic product.

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LorLee,

It is painful, but Jerry and Scott likely are correct!

I am a great believer in good paint and good painters. I certainly can't see the entire job from your photos, but what I see looks a little on the skimpy side.

The solution now would be; scrape, prime and repaint with the good stuff. I don't know of any magic product.

Good stuff really cant't be found at Lowes or Home Depot! Sherwin Williams, Ben Moore and Pratt & Lambert make some of the better paints, IMVHO.

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LorLee,

It is painful, but Jerry and Scott likely are correct!

I am a great believer in good paint and good painters. I certainly can't see the entire job from your photos, but what I see looks a little on the skimpy side.

The solution now would be; scrape, prime and repaint with the good stuff. I don't know of any magic product.

Good stuff really cant't be found at Lowes or Home Depot! Sherwin Williams, Ben Moore and Pratt & Lambert make some of the better paints, IMVHO.

Agreed! I like Sherwin-Wms and a local company.

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Thank you so much. I really appreciate it. I read elsewhere on this site about the importance of good paint,and the brands you like. We do have a Sherwin Wms store nearby... We'll make sure whoever we hire does it right this time.

Have a great weekend, and thanks again!

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I agree with John, condensation inside the wall due to lack or bad insulation and/or vapor barrier. Who knows what these boards are hiding.

As you all know, mildew is the product of a combination of many factors. Absence of mildewcide in the paint will not make mildew appear out of the blue. It simply protects the cellulose in the paint film from being eaten away by those micro-organisms.

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As you all know, mildew is the product of a combination of many factors. Absence of mildewcide in the paint will not make mildew appear out of the blue. It simply protects the cellulose in the paint film from being eaten away by those micro-organisms.

I still think it is a paint issue. The paint is peeling along the edges.

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We have a recurring problem, after treatment (JoMax, bleach) and even fresh paint, with a black mildew that shows up on the side of our house every year (some years better/worse than others).Oddly, the sunniest side gets the most... it IS the side that faces a river, about three blocks away. Cleaning it every year is crazy, and almost has us thinking about siding (Hardi Plank maybe?). It's a 3 story house, 1800s, wood... New England. We don't notice it so much on other houses but many of them are vinyl sided.

It's algae. The original posts sez the sunniest side gets it the most - it's not from moisture or condensation. Replacing wood with fiber cement siding won't fix it. The best brand of paint won't fix it.
Any suggestions? Is this just something that happens? Thanks!
I've got it on the southwest facing sides of my home, that happen to be facing a large pond. Spray sodium hypochlorite to kill it and scrub with TSP to clean it but, it will come back again.
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I agree with John, condensation inside the wall due to lack or bad insulation and/or vapor barrier. Who knows what these boards are hiding.

As you all know, mildew is the product of a combination of many factors. Absence of mildewcide in the paint will not make mildew appear out of the blue. It simply protects the cellulose in the paint film from being eaten away by those micro-organisms.

A casual conversation with a 'house guy' also made us wonder about condensation. We have zero insulation in the walls. Perhaps no vapor barrier. So IF that's it, the answer is to ... pull off the boards, insulate and put them back on, 'treat' them and paint them? (By 'treat' I mean, kill with a solution I guess?)

If that's the issue and we don't do the insulation, and pay for an expensive painting job, it will just keep coming back, right? I wonder how much we would pay someone to spot clean each year... ? Hmm.

Should an insulation specialist be able to tell us if this is the problem?

Thank you all for the awesome help!

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It's algae. The original posts sez the sunniest side gets it the most - it's not from moisture or condensation. Replacing wood with fiber cement siding won't fix it. The best brand of paint won't fix it.

Any suggestions? Is this just something that happens? Thanks!
I've got it on the southwest facing sides of my home, that happen to be facing a large pond. Spray sodium hypochlorite to kill it and scrub with TSP to clean it but, it will come back again.

Is your black in color? Interesting we both face bodies of water ...

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We have zero insulation in the walls. Perhaps no vapor barrier.

Well, if that is the case, don't look any further. You need an envelope specialist.

Umm... what does that mean? Do you mean insulation specialist? Does that seem crazy? Our house is surprisingly cozy, we use less oil than many people, but we know the walls don't have insulation. Not any more than the bare minimum needed, i guess. Will double check w/husband on that. Do you think that's it? Are you saying that if there is no insulation, this kind of mildew is common?

Feeling like such an ignoramus... Appreciating the feedback!

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It's algae. The original posts sez the sunniest side gets it the most - it's not from moisture or condensation. Replacing wood with fiber cement siding won't fix it. The best brand of paint won't fix it.

Any suggestions? Is this just something that happens? Thanks!
I've got it on the southwest facing sides of my home, that happen to be facing a large pond. Spray sodium hypochlorite to kill it and scrub with TSP to clean it but, it will come back again.

Is your black in color? Interesting we both face bodies of water ...

Yes, it's black. We've also got 2 shades of green in other areas on unpainted wood.
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It'd be surprising not to have insulation at all but there could be some missing or could simply be inadequate and the absence of vapor barrier is quite possible also. Those plankboards could also have been installed without any air space behind.

The walls, ceilings, floors and roof of a house are what we call the envelope. Those components have to meet minimum construction standards. If the envelope is compromised in any way or does not meet minimum standards, that can lead to problems.

As far as the paint is concerned, I used to own a small paint manufacture back in the 80s and it's true that the mildewcide was removed from the formulas. Some had problems adjusting back then but it's not supposed to pose any problems today. For the mildew problem to be recurrent every year, it means humidity is coming from behind (inside the wall). The paint will act as a vapor barrier and emprison it until mildew appears and will then be eaten away. Humidity will also make it peel off due to lack of adherance.

You need to find out how this humidity is formed in the first place. This is why an envelope specialist would be needed in your case. He will check the construction of the walls by doing a localized deconstrutive investigation and will make recommendations.

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