Black Mold & Air Return?


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Old 10-02-08, 03:19 AM
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Black Mold & Air Return?

Hello. This is my first post here. I did searches of previous threads but didn't find anything I thought applied to my situation. Sorry if this is a repeat.

I live in a climate that's very humid in summer and has long, frigid winters. Our home is only a few years old. One bathroom is over the garage and it has a black mold problem. It's under the chalk, in grout, and grows inside the toilet. Very concerned about the health issues associated w/this type of mold.

We've done the typical things, such as replacing the chalk, using the bleach tablets in the toilet, using the vent, using an air purifier, and spraying peroxide in the shower after use. The mold comes back.

We've also got what the builder calls an "air return vent" next to the toilet, where the mold is worst. All it is is a hole in the wall covered with a metal grate. We've put filter paper over it to control dust and debris.

So my questions are:
  1. Is it likely this air vent is causing the mold? I've read sealing things up is a way to prevent mold, while others say venting is needed.
  2. Should I change anything about the vent, and if so, what?
  3. Is there anything else I should do to control the mold? I am thinking I need to remove the chalk again, clean everything with a bleach-water solution, and re-grout. Do I need a specialist at this point? Do I also need to repaint using a mildew inhibitor paint, even though there is no mold on the walls?
:helpme 2:
 
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Old 10-02-08, 04:51 AM
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There should be no return grille in a bathroom. This is against code in most areas and I would bet it is in your as well. 2nd by a cheap humidity gage and set in in this room. Knowing what the RH is is the most important thing. Does this bath get used? How long do you keep the bath fan on after showering? My first reaction is you have an infiltration problem from the garage because you are saying there is mold on the floor. Is the floor Insulated? Is there sheet rock in the garage? Is the sheet rock sealed?
 
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Old 10-03-08, 07:38 AM
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Thanks for your reply.

I questioned the builder about the vent at the time and he insisted it is necessary to get fresh air inside. I've never seen anything like this. I insisted upon an independent inspection and nothing was said about the vent. I just checked our building codes online and can't find anything about venting. So do you recommend I seal it up?

Also--I want to clarify. This grille does not attach to any sort of ductwork. It opens into an empty wall (wall between a tub and the toilet room). I can see the bottom of the tub when I look into the grille. Is this normal? (FWIW, the tub is on the outside wall of the building.)

The tub does not get used often but the shower (in the same room as the tub) gets used daily. The vent is used daily too.

The garage is sheetrocked and I believe the floor is insulated. The mold is mainly in the toilet and in the caulk of the shower (which I obviously misspelled earlier!). There is one spot on the wall grout it regularly appears too, but the mold is not on the floor except in the caulk.
 
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Old 10-03-08, 07:29 PM
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Return in a wall cavity is fine! Can you post a pick! Sure would like to know the RH in the room.
 
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Old 10-05-08, 08:31 AM
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My camera is broken....I have no way to measure the RH, which I am guessing means "relative humidity", but it always feels damp in there.

Now my roommate says the builder told her the purpose of the hole was to allow access to the Jacuzzi motor in case it needed repair. This does not sound plausible to me. The hole isn't big enough for a person to access the motor.

I guess we are going to find some way to cover up the grille, remove and replace the caulk, and possibly regrouting.

We've also discovered the toilet has been leaking a bit so we are working on that too.
GI2
 
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Old 10-05-08, 09:00 AM
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Make sure when you use the shower bath fan runs for at least 20 minutes after you finish.
 
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Old 10-05-08, 02:10 PM
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Some years back the Washington state building or energy code specified that new construction had to have what they called a wall port. This was a vent from the outside to allow the exhaust fans to work in the well sealed houses that the code mandated. I think that has now been superseded by a requirement for either some kind of fresh air intake on the heating / cooling system or maybe air-to-air heat exchangers.

It's possible that this is what your "air return vent" was for.
 
 

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