Mold on Sheetrock - Contractor Talk - Professional Construction and Remodeling Forum

Tonyeo · 11-05-2009, 09:21 PM

Need some help, I noticed in my kids room some mold on the drywall, no problem I thought, tear the rock off, find the leak, repair it, re insulate and re rock, now what I was not expecting was condensation (water) on the poly on the warm side only on the bottom where the mold is, insulation completely dry, nothing running down the wall, any ideas as to what can be causing this, one thing I did notice is that the poly seems to be tucked under the hardwood floor, there is a basement underneath. There I was expecting to replace the insulation maybe the studs if they were wet and found this. Any ideas.

Tonyeo · 11-06-2009, 10:11 AM

I just pulled off another piece of rock on an adjacent wall and it is foil backed, with a poly vapor barrier as well, would this constitute a double vapor barrier ?

mics_54 · 11-06-2009, 04:28 PM

Quote:

I just pulled off another piece of rock on an adjacent wall and it is foil backed, with a poly vapor barrier as well, would this constitute a double vapor barrier ?

No.

Condensation can occur on wall with or with out a vapor barrier. The condensation is from warm air coming in contact with a cold surface. In your case warm moist air in your house is coming in contact with the cold surface located at the bottom of the walls.

The problem could be poor insulative values at the bottom wall plate or rim joist at the floor. And of course warm air tends to rise in your house making the floor cooler than the ceiling.

Exterior walls tend to stay cooler and this set up a downward air current at the exterior walls as the air cools. Warm air cooling as it contacts a cool surface is what causes moisture to form on the walls.

It has nothing to do with a vapor barrier. The vapor barrier is to keep warm moisture laden air from entering the wall cavity and condensing on the outer surface of the exterior walls.

The solution in your case is to make the bottom of the walls in the problem area stay warmer...or...adjust the humidity in your living space...or other wise eliminate the dew point from occurring.

KennMacMoragh · 11-06-2009, 04:39 PM

I would put some PVA primer on the drywall too when you replace it. Because it sounds like the vapor is going through the sheetrock then stopping at the plastic and then building up inside the sheetrock because it has no where to go. But PVA would stop it from even going into the sheetrock.

Tonyeo · 11-06-2009, 06:27 PM

This is in a closet so I am pretty sure the airflow is bad as well, I will get a humidity thermometer and see what that says, but I am thinking that is a problem as well. I am putting in blue board (moisture and mold resistant) so hopefully this will help. It flummoxed me last night but in the cold light of day I believe it is high humidity and a number of other factors like the airflow. I will pva it as well and just keep a closer eye on it.

KennMacMoragh · 11-06-2009, 07:59 PM

Sounds good, take all precautions when doing a fix. Not sure what you can do about the humidity though even if it is high, unless theres a water source coming from somewhere. I had an issue with my air conditioning leaking once which later created mold all over the wall. But it's obvious something is wrong when I see mold growing, don't really need a humidity detector.