Mold Prevention Strategy

[TromboneAl]

In our humid environment, I'm always battling rust and mold.

I'm mostly winning, by using a dehumidifier in the bathroom, making sure there are no pictures on exterior walls, and moving furniture a foot from the wall.

I recently discovered some new mold on the wall in a room we rarely use.

Remember that the theory is that air hits the colder surface of an exterior wall, and moisture condenses onto the surface.

Here's my new strategy for preventing it, which I haven't seen mentioned on any anti-mold web sites:

I put a small desk fan on the floor, aim it at a problematic location, and leave it running 24/7. The idea is that it circulates the air and prevents buildup of moisture in some locations.

With a 20 watt fan, this will cost about $24/year, but I'll put a fan speed control on it, and cut it down to about 10 watts.

Do you think this will be effective?

 

[samclem]

Do you think this will be effective?

It depends. If using the fan to push more room air against the wall causes the wall's surface to warm up to something above the dew point of the air, then the water vapor won't become liquid right inside the wall covering and you might avoid mold. But if the wall's inner surface remains below the dew point of the room air, then causing more air flow over the wall might >increase< the amount of water on the wall.

Decreasing the relative humidity of the air inside the house is the best solution--it takes care of moisture on the walls as wel as in the closets and everywhere else. Reducing the RH can be done by:
- Reducing introducton of water into the air inside (no unvented combustion appliances, use stove vent fans, venting clothes driers outside, use bathroom fans when showering, etc).
- Mechanically removing water (as you are doing with a dehumidifier or with an air conditioner)
- Increasing the temperature of the air inside the house
- Ventilating on the (rare) occasions when air inside the house has more moisture than air outside.

It's great to see your posts, Al!

 

[sailor]

In general air circulation helps, but if it just stirs highly saturated air from one place to another it will not.
For a quick test put a moisture meter in the troublesome spot and measure with fan off for a day and with the fan running.
I can recommend these: Amazon.com - AcuRite 00325 Home Comfort Monitor, Black
I used (and keep using) few of them placed in various places in the house to determine placement and operating schedule of the dehumidifier.
(And they are fine running on Eneloop batteries)

 

[TromboneAl]

Thanks for the help.

The fact that the mold only develops down low on the wall or behind a picture frame makes me feel that exchanging that air with that in other parts of the room will help.

Dehumidifying or heating the whole house would be pretty expensive.

I have a few moisture meters which I've calibrated, perhaps I'll try some experiments, but humidity changes from hour to hour.

I suspect I'll never know for sure what works. The room with the new mold has been fine for 14 years, and another room that used to have a problem is now in good shape.

 

[bld999]

What changed after 14 years? That would start me hunting for a reason. Did you re-roof or make any changes to the exterior, new paint for example?

 

[ERD50]

I have a few moisture meters which I've calibrated, perhaps I'll try some experiments, but humidity changes from hour to hour.

Since you aren't so averse to spending money these days (and this would be an 'investment' in your home), how about one of these (or something like it, I just did a quick search):

Lascar EL-USB-2-LCD Humidity, Temperature and Dew Point USB Data - Amazon.com

Looks like it can record standalone with a timing you set, then later collect all the data at the computer.

Interesting calibration technique you linked. I guess the water and air and the saturation point of salt all work together to provide 75% and still absorb anything higher.

-ERD50