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Old 03-08-2011, 09:48 PM   #1
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Mold strategy


I'm attaching below a photo of a joist cavity with mold, this cavity is in the floor under my kid's bedroom and it is also the ceiling above the bathroom below. The bathroom has an exhaust fan in the exterior wall and it works and is not obstructed. I've fogged Concrobium into the joist cavity.

So I'm looking for suggestions as to what the sources of moisture I need to deal with could be, if any, before I do air sealing on this joist cavity (or will that help?)
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Old 03-09-2011, 12:33 PM   #2
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Mold strategy


Wow! If it were me, I would try to find/eliminate the source of moisture, but the ceiling in the bathroom would have to come down, and possibly a complete gut of the bathroom. You more than likely have a lot more mold/fungus growth than that in adjacent joist bays and possibly in your bathroom wall cavities if you have that much of a moisture problem in that bathroom. Hopefully someone with more mold removal experience will chime in, but from my experience with tearing out improperly built bathrooms/showers/tubs the only way to remediate is to tear it out, clean it up, and rebuild it properly.

I think I'd move the kids to another bedroom in the meantime. I've never used Concrobium before, is that a picture prior to using the concrobium, or after?


Last edited by littlecleo; 03-09-2011 at 12:39 PM.
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Old 03-09-2011, 02:38 PM   #3
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Mold strategy


You have got a serious mold issue there. First you need some moisture testing to help pinpoint the source. Mold needs 60% or greater humidity to thrive. Finding the source of that much water should not be difficult. Next you need to probably tear out the ceiling. Any drywall ceiling that has been exposed to that degree needs to be gotten out. Fogging has not been proven to be particularly successful in killing mold in porous materials such as you have. In addition, even if you've killed it, you need to remove it. Even dead mold carcasses can be allergens. Scrub it down with a good cleaner. That means scrub brush, wipe down, HEPA vac it, and get it dry. Then apply a fungicide. After that dries, apply a sealer. Install a new ceiling. First and foremost, you need to control the moisture. Otherwise, it will all be back again. I would not be surprised to find the same conditions in the wall cavities as well. And remember, bathroom exhaust fans don't do anything until you turn them on.
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Old 03-09-2011, 03:20 PM   #4
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Mold strategy


As far as the source of moisture, what about someone not running the fan?

As to removal -- if it's contained within the cavity/ies, then it's contained. Is it manifesting itself on the other side of the drywall? If you can solve the moisture problem, then the mold will stop growing. It won't go away, but neither will it spread -- assuming you don't have openings that connect the interior of the cavity to your living space.

Now if you want to tear it out for peace of mind, go for it.
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Old 03-09-2011, 05:13 PM   #5
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I wonder if the moisture source is from the bathroom only? You have a side wall vent but what if its suckage is just not good enough to get the moisture out? I would want to vent at the ceiling close to the shower/tub area to get that moisture out asap. What if the vent itself is leaky within the sidewall and it is sending moisture up to this area? If that were the case, I would say remove the drywall very carefully at the vent location and see if mold exists. If leaky, i would expect a lot of mold there.

If the mold is contained, and it is not being fed anymore, maybe no harm. If kids are sick a lot, then remediation is called for.

Other moisture getting in there: What about openings from the basement. A very damp crawlspace or basement? Any kitchen vents? I am reaching a bit but if the main source is the bathroom moisture, you have to go after that. Is it possible that outside air is getting in and condensing in warm spaces?
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Old 03-09-2011, 07:40 PM   #6
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Really, identifying the moisture source is the kind of guidance I am looking for here. I actually plan to build a new bathroom at a different location, after which I will tear out this bathroom to build a stairway at the bathrroom location. I'm looking to see what I can do in the mean time where it can be done quickly and easily.

So I don't know the history before we purchased the house in August of last year (2010), we've been consistently using the exhaust fan during showers because it's a somewhat smaller bathroom and the mirror fogs up. I can't speak for how well this was done before.

The shower head is located very close to the ceiling, the previous owner was tall so we suspect that's why the shower head is so high. We're talking the pipe coming out of the wall at about 4-6" below the ceiling. This is on the suspect.

There are 4 adjacent ceiling joist cavities with mold. The cavity pictured is the worst cavity. The wall cavities have fiberglass batt insulation with kraft faced paper. From the portion of the floor cavity exposed in the side attic, I can see that the bathroom drywall of the ceiling seems to have a plastic sheet vapor barrier.

The roof was in very bad shape when we bought the house, I have redone the roof. I'm not sure this was related because the mold problem is focussed above this bathroom.

I do know that I need to work on roof ventilation. I installed ridge vents while working on the roof and I installed rafter baffles, but I need to increase my intake ventilation.

I don't have a basement, I have a crawlspace with a dirt floor. The driveway immediately next to the house is in very bad shape, and it slopes towards the house. Under the driveway is a collapsed sewer main. At the time the house was purchased, the sewer pipe was obstructed and when water was used in the house, the system backed up onto the crawlspace dirt out of the drainage point for the humidifier, which is mounted to the furnace which is in the crawlspace. The plumbing is clear and has been rebuilt so the humidifier operates with a condensate pump so it has a higher drainage point and is less likely to allow a backed up sewer to result in backflow into the crawlspace.

All but one floor joist under the first floor have been sistered due to rot at the rim joist. All of these rotted joists are replacements. Floor joists under the bathroom are mostly 3 boards thick except for 1 which is 4 boards thick and 2 which are single boards which are cut at the toilet and bathtub drain without proper support.

I suspect it is possible that moist air might be drawn through these cavities and out the ridge vents, and if so I might stop the flow by air sealing the joist cavities. On the other hand, my concern was that this would only impair my access to do anything about the mold.

I also suspect it might be possible that this mold has been there a long time and isn't related to any existing conditions or might be related to something I've already corrected.
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Old 03-10-2011, 07:38 AM   #7
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You mention that the drywall ceiling has a plastic vapor barrier. In post #1, you say that the area above is the floor of your son's bedroom. If I read this right, you have a vapor barrier on an inside ceiling. That may help you to pinpoint. Is there mold only in the space above the plastic or is it also below (both sides)? Have you tested anything for moisture content? That should be a first step. Find out what materials are damp enough to support mold growth. Test several areas, both in the moldy areas and outside, so you can get a baseline. That will help greatly in pinpointing a source. As far as the existing mold, if the moisture test shows that everything is normal, then you have a dormant colony. The problem is that even dormant, it will continue to spew high levels of spores and bits of mold components into the air. Remember, these are microscopic so they'll move through the tiniest holes and cracks. That volume of mold needs to be cleaned up and eliminated. You don't want to be breathing that kind of crap. Secondly, even if dormant, it is not dead. If you happen to have another moisture episode, it will reactivate. Even if the fogging was effective on the stuff you see on the surface, I would bet that it is not 100% dead. And what is dead will break down sending fragments everywhere.
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Old 03-11-2011, 08:51 AM   #8
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Well, again access is an issue, I don't know that I can get my arm far enough into there to reach all of this, maybe some of this, but I would definitely be working blind... When it gets to the point I tear things open for access, I intend to just go to town replacing anything and everything that is affected.

Is there anything short of replacing the joists and subfloor that would eliminate the mold?
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Old 03-11-2011, 09:18 AM   #9
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If you open it up, your best best may be to call a pro out. It may be expensive but this is one of those times... : - (

There are sprays that can be applied but I don't know if an avg joe get that type of stuff. Maybe you can. I see no reason to remove any structure or wood at this point. It appears that all the mold is just on the surface.
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Old 03-11-2011, 02:11 PM   #10
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There is really plenty of reason, mostly structural, and it's in the plans but before I start that level of work on the second floor I need to get the foundation then the first floor in order.

It's almost remarkable that the floor under the bathrrom doesn't have mold since it's over the area where water seeps up from the ground and the whole floor has seen numerous repairs to rotted structure, but aside from disintigration the wood under the bathroom doesn't have signs of mold. Other floor joists under the living room have some whitening, but not as extensive as these photos. These floor joists are also planned to be replaced.


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