Indoor Humidity and Building Materials?
 

Does anyone know if plaster keeps moisture/humidity in better than drywall? As opposed to the summer, when temps are high and RH plummets, I've had no problems keeping humidity up (45-65%) in my room this winter. Even when it's the same temp inside as outside, I can have humidity be 20-30% higher inside. I've noticed that if I open up my room for a couple hours for fresh air at night when humidity is higher here and then close my door and windows. The moisture will stay in the room for at least a day as long as I don't leave my door open to the rest of the apartment (if I do, the humidity will start dropping rapidly; more than 5% in a matter of minutes).

I've never experience this before, but I used to live in the desert and my house had drywall. The apartment I've been in for the last year has thick plaster walls and I'm wondering if this could be the reason the room holds moisture in so well. Does anyone else here have plaster walls and notice this effect?

I have plaster walls but it could just be the room. When the rest of my house is fine my study is always much warmer and more humid.

Plaster retains and evaporates moisture only when it's very new. Once it dries out, several months later, it's no different from painted drywall. Both plaster and drywall breathe, however, so if the walls of the house have a high moisture content, this humidity will be transmitted through the plaster or drywall to the living spaces inside.

If your walls are painted they most likely have been sealed with primer.

It seems to me that your room is sealed very well if your humidity is not fluctuating with it sealed(door and windows).

The most logical thing is that at night when the RH comes up it fills your room. Then you seal it so the moisture has no where to go but stay in the room. Open the door and the RH dissipates.

Now with that said... no air movement can be a bad thing. Make sure you have a fan running.

I grow my plants in my drywall bedroom with RH of 65%-70% and temps from 65F night to 75F-80F day. I have my door always closed and all vents are closed. I have a ceiling fan and fan on a stand always going on medium to high speed. I sleep in this room and have gotten used to the higher temps and humidity.

Building is at least a few decades old. There's a Wedgewood stove in the apartment next door; I wouldn't be too surprised if this building dates back to the late 50's-early 60's. So, the half-inch or so layer of plaster is definitely old. Didn't think about the paint being the cause, but that's probably it. It looks new and on the corner of the closet door, some of the paint is peeling and I think it might be latex-based, which I don't believe really breathes a lot and there are who knows how many more coats of old paint underneath it.

Haven't had any rot problems here but should probably have more air circulation than just the 7 fans in my computer :lol: or my space heater. *Sigh* need to see if I can get a new plastic retention clip from the manufacture that broke for my ceiling fan when it was taken down from my place. Works fine but the slight wobbly noise can be a little annoying when I want silence. Well, I've also got plenty of portable fans no one bothers to use in the winter :) . One or two of those should do the trick if the noise starts to bug me or when I'm sleeping.

Do people usually run their fans all day in the winter? Humidity is staying around 50-65% and temps 60-80F (inside, 40-80F outside)for now. Now, summer is a different story, my orchids (and I) had to deal with a range of 60-100F inside and humidity as low as 30% and I almost always had fans on for us.

I run my fans all day long, all year long.

I run one oscillating fan in my plant room 24/7, strictly for air circulation. Aimed so that there is slight leaf movement around the room.

Also have an exhaust fan and outside air intake fan. Both fans runs 24/7, but the outside air intake gets shut down in the winter and outside fresh air is allowed to enter the room passively.

Generally I would think a properly painted/sealed plaster would keep in moisture better than painted/primed drywall in an identical climate.

I thought that if you have constant high indoors RH you run the risk of having a mold problem develop ?
I only found this out when reading about my whole-house humidifier and why you cannot set the gauge on any setting above 50%....