Why is my neighbor's A/C causing my walls to sweat?

Question

Whenever my neighbor runs their air conditioner for an extended period, my room, which shares a concrete wall with theirs, experiences condensation issues (my wall starts to 'sweat'). After investigation, it appears that the concrete walls in the entire building are too thin, causing a temperature contrast between the cold air on their side and the warm air on mine.

Contractor's Idea: So, this contractor suggests doing this in both sides of the concrete wall

1. Scraping off the current stucco on the walls.
2. Washing the walls with bleach.
3. Applying three layers of wall waterproofing, with a 24-hour interval between each layer.
4. Applying at least three layers of plastic stucco.
5. Sanding the walls and preparing them for paint.
6. Applying paint.

They say it'll take about a week.

Wondering if you guys have dealt with this or have thoughts on the plan. Does the idea sound legit? Any tips would be gold.

Thanks a bunch!!!

Answer 1

This plan seems to assume that water is coming through the wall from the neighbor's side to yours.

If the problem is caused by temperature-based condensation, this has no hope of working, because the condensation will be using water from your side of the residence - there is no "passing through" of the water.

If you haven't done so, consider running a dehumidifier in (one of) the room with the common wall. Stripping the moisture from the air might show if the issue is purely condensation, or if some water passage is involved.

Another possibility is to install some kind of water-resistant insulation. For example, rock wool doesn't care about water. You might still have a condensation issue, though, so you would need some mechanism to capture and drain the water.

If you have the ability to make changes to the neighbor's side, installing insulation on that side might be a better option - trying to put the condensation line somewhere in their space.

Finally, have you any understanding of what temperature setting the neighbor is using on their air conditioning? Could this problem be solved by changing a damper or redirecting airflow on their side? Or just asking them to reduce the air conditioning amount?

Answer 2

A much simpler solution here would be to add thermal insulation to minimize the heat transfer pulling your side to below the dew point.

None of what that contractor is proposing is adding thermal insulation. All they are doing is trying to handle the moisture when it is going to happen again.

Adding thermal insulation can be done by Stickframing a wall next up to the concrete on one side (preferably their side), pulling the electrical boxes to the new wall surface, adding a vapor barrier, shoving in insulation and then drywalling over the entire thing.