# Moisture on backside of switch covers



## CountryB (Aug 4, 2016)

I don't know if this is right place to ask this question (is it an Electrical question or a Building/Construction question?) So feel free to move this post.

1) My wife noticed some drywall staining around the electrical light switch cover in the guest bedroom (on the wall next to the exterior sliding-glass door that leads to patio). I took the cover off, and the backside (inside) of the switch cover had moisture on it (like dew). I didn't see any moisture or corrosion on the switch itself.

2) In the 1/2 bath there is a water stain that runs down from the light switch for the outside door light. This switch is on an exterior wall next to a door that leads to patio. I thought someone with wet hands used the switch and left the stain - but wife says she cleaned that stain off once, and now its back.

My house is block/stucco on slab in central FL. I am the original owner and have been in the house for 26 years.

A) Is this moisture coming from inside the wall (transmitting through the stucco, perhaps)?

B) Could this moisture be from inside the room (high humidity in room)? But if so, why is on the inside of the light switch cover.

I'm thinking maybe the exterior paint on the stucco is too old now and letting moisture through it - and I need to repaint. However there should be a vapor barrier on the inside surface of the cinder block between block and drywall (I have seen this barrier in another room that I remodeled. It looks like craft paper with aluminum foil backing on the side facing the exterior).

Any thought or suggestions on how to figure out what is going on?


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## Windows on Wash (Aug 30, 2011)

I would start looking at source A. How has the weather been of late? 

How is the venting of the space handled?


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## SPS-1 (Oct 21, 2008)

What temperature do you keep your AC at?

You can sometimes get the situation where its hot and humid outside, and cold indoors, and an air leek from the outside can lead to condensation on interior surfaces.


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## CountryB (Aug 4, 2016)

Windows on Wash said:


> I would start looking at source A. How has the weather been of late?
> 
> How is the venting of the space handled?


I'm in central FL. Weather is hot 95 degrees and humid. There is an afternoon thunderstorm everyday. 

The house is single story block construction with vented soffits and a ridge vent. Attic insulation is installed on floor with blown on top of that.


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## CountryB (Aug 4, 2016)

SPS-1 said:


> What temperature do you keep your AC at?
> 
> You can sometimes get the situation where its hot and humid outside, and cold indoors, and an air leek from the outside can lead to condensation on interior surfaces.


AC is set to 76 degrees. 
I wouldn't be surprised if there were air leaks all over the place. The house was built in 1990 and "tight houses" weren't the norm. Maybe I should have a blower test done.

I'm surprised that I'm just now seeing this problem (maybe it has been going on for years).


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## SeniorSitizen (Sep 10, 2012)

It's rare that the dew point temperature reaches 80°F, but I'm seeing 81° DP in The Villages and 75° in Orlando at present. If outdoor air is reaching the back side of the plates dew forming there is a real possibility. Try raising stat temperature above DP temp. and run ceiling fans when those conditions occur.

http://www.usairnet.com/weather/maps/current/florida/dew-points/


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## hkstroud (Mar 17, 2011)

I suspect that you have a leak in the wall (or the roof) somewhere. Remove the cover plates for a time and see what happens when you have a thunderstorm. If you have a leak you will see the moisture. If it is condensation you won't.


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## Bud9051 (Nov 11, 2015)

Hi country,
Since you are not new to this home (26 years) I tend to think as hk said, a leak. But, being block construction, moisture that gets into the blocks can turn to moisture vapor and travel throughout the walls. Now, I'm from way up north and stucco hasn't been discovered as yet up here so I can't say as to whether the moisture is coming through the walls, as you questioned, or from the roof. But moisture is getting into the block walls and what you are seeing (as stated) is condensation.

Those more familiar with the protection the paint affords will have to answer that question.

Bud


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## FrodoOne (Mar 4, 2016)

CountryB said:


> 1) My wife noticed some drywall staining around the electrical light switch cover in the guest bedroom (on the wall next to the exterior sliding-glass door that leads to patio). I took the cover off, and the backside (inside) of the switch cover had moisture on it (like dew). I didn't see any moisture or corrosion on the switch itself.
> 
> 2) In the 1/2 bath there is a water stain that runs down from the light switch for the outside door light. This switch is on an exterior wall next to a door that leads to patio. I thought someone with wet hands used the switch and left the stain - but wife says she cleaned that stain off once, and now its back.
> 
> ...





CountryB said:


> Weather is hot 95 degrees and humid. There is an afternoon thunderstorm everyday.


You will note that I am in Australia and the only time that I was in transit via Miami airport to a Caribbean island was over 10 years ago.
However, at that time I was amazed that, before 9 AM - in late July - in Miami airport, with a "comfortable" temperature inside the terminal, the large glass windows were dripping with moisture on the outside, due to the condensation of the external humidly on the outside surface of the single glazed windows!

I suggest that with your "comfortable" inside temperature of 76˚F (24.5˚C), the cooling of (virtually "saturated") external humid air from 95˚F (35˚C) on the back of the plastic switch-plates is causing condensation of moisture, which then runs down the inside of the sheet-rock of your walls.

From this, I strongly suspect that outside humid air is leaking into any cavities in your walls and causing this problem.

(By the way, we run our A/C at 26˚C (about 79˚F), which we find quite comfortable - and economical - when dressed for Summer.)


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## SeniorSitizen (Sep 10, 2012)

To add to my original suggestion, there is another possibility to prevent this, but the list could also go on and on.

If a slight in house positive pressure could be created by running the blower during the high outdoor dew point temperatures, that humid air contacting the switch plate would be prevented from entering those switch cavities.


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## CountryB (Aug 4, 2016)

Thanks for all the suggestions. 
I'm pretty sure I don't have any roof leaks, but I wouldn't be surprised if there were many places where the hot damp outside air is leaking in. I suppose this issue has been going on a for while. I just didn't notice it until now. Maybe its normal for older FL homes.

I'll be watching these two switch boxes more closely now (and I'll check the others too). 

I can bump the AC up to 78 (small change) but might help. Anything higher than 78 won't be acceptable by family (mostly me).

Thanks again for the ideas and suggestions


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## Shakeyd36 (Jul 5, 2019)

Have you ever found out how moisture was getting behind your light switch covers ?
I’m having the same problems. Thanks in advance .


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## Bud9051 (Nov 11, 2015)

AC makes the inside of the house and those switch covers cool. Warm humid air from outside leaking into the wall cavity will form condensation on the back of those covers.

Bud


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## Shakeyd36 (Jul 5, 2019)

What would be the best way to solve this ?
It’s leaving marks on the drywall by the covers .


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## Bud9051 (Nov 11, 2015)

Simple problem but not easy to fix. Basically you need to stop the outside air from reaching that electrical box. First thing I would try, since you cannot remove the siding, would be to block the opening the electrical box is providing. You can stop the flow of water through a hose by blocking either end.

Here they make foam backers to fit behind the switch plate cover, that might help. I go a step further and cut out a piece of contact paper to cover the entire area behind the plate minus a cutout for the switch. The contact paper does a better job of sealing between the box and the drywall. In some cases I have left a 1" boarder around the plate to accommodate larger plates and ensure a good seal. In one case it reduced the fingerprints from the kids. Contact paper comes in a variety of colors.

Bud


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