# What's Causing Shadowing at Wall Studs ?



## CApainter (Jun 29, 2007)

I've noticed shadowing on interior walls that share exterior side exposures. I've explained it as some sort of static attraction that concentrates airborne particulates to where the steel studs are. 

The interesting thing is, I've painted over it with interior latex at other locations, and have not noticed any shadowing. Even seven years later. The picture attached is of an original painted wall about 18 years old.

Does anyone have an explanation for this?

Thanks, 

John


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## Delta Painting (Apr 27, 2010)

Lack of moisture barrier...


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## CApainter (Jun 29, 2007)

Delta Painting said:


> Lack of moisture barrier...


The shadowing is occuring on two different buildings with two different exterior finishes. One building is stucco and the other is metal. As far as I know, both have had a moisture barrier and insulation installed. It is also not showing any evidence of having moisture content. 

It is a strange anomoly in that it doesn't occur on divider walls, or ceilings. However, one metal ceiling that has little space between the roof sheathing and drywall ceiling, other than the width of the metal joists, shows the same shadowing.

As I mentioned, it does seem to be remedied with a coat of interior latex, but the phenomena is strange.


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## Allsurface (Aug 17, 2014)

It's called ghosting, I've have run into this a couple of times.
Poor insulation is the root of the cause.
The studs become cold and attract moisture from in the house and household dust will be attracted to that.
It is that simple. 
Stain blocking primer and regular paint, a higher sheen may wipe down better in future.
Metal stud or wood doesn't matter. High humidity inside adds to problem. 
Note, unless they fix the problem it will recur. 

Google ghosting.


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## Delta Painting (Apr 27, 2010)

CA, It may be lack of ventilation\ insulation allowing the the fine dust and and other indoor contaminants in the air to accumulate in the areas showing. I have only see this on exterior facing walls and on some ceilings..


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## CApainter (Jun 29, 2007)

Great feedback guys! It looks like it may be a combination of what you've explained. I certainly get the radiant cold issue and the lack of ventilation. 

It seems like this may be a tough one to guarantee without some reconstruction.

Thanks!


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## Gough (Nov 24, 2010)

Thermal bridging is what causes the ghosting. The studs, whether metal or wood, are more conductive than the stud bays. As Allsurface posted, the cooler surfaces by the studs allow more condensation than the other areas and collect more airborne particles. This become especially noticeable in houses with wood heat.

The ultimate solution is insulated sheathing on the outside of the house, something seen more often in new construction. That acts as a thermal break, slowing heat loss through the studs.

Here's a pair of images with the right-hand one taken with a thermal (infrared) imager. You can see the temperature difference.


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## Gough (Nov 24, 2010)

CApainter said:


> Great feedback guys! It looks like it may be a combination of what you've explained. I certainly get the radiant cold issue and the lack of ventilation.
> 
> It seems like this may be a tough one to guarantee without some reconstruction.
> 
> Thanks!


It's not radiant, it's conduction, and ventilation likely has nothing to do with it.

You're right, the solution is reconstruction...and it's not cheap.

What it typically involves: remove exterior cladding (siding, stucco, brick, etc) and exterior trim. Either replace all windows and doors, or reset them and add jamb extensions. Add thermal sheathing. We usually use foil-faced polyisocyanurate sheets. Either tape seams or install WRB. Install spacers for ventilated rain screen, if possible. Install new exterior cladding.

Unless there are a host of other issues, repainting periodically is cheaper, by several orders of magnitude.


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## slinger58 (Feb 11, 2013)

Gough said:


> Thermal bridging is what causes the ghosting. The studs, whether metal or wood, are more conductive than the stud bays. As Allsurface posted, the cooler surfaces by the studs allow more condensation than the other areas and collect more airborne particles. This become especially noticeable in houses with wood heat.
> 
> The ultimate solution is insulated sheathing on the outside of the house, something seen more often in new construction. That acts as a thermal break, slowing heat lose through the studs.
> 
> ...


Just curious, is that because of airborne ash/soot?


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## Gough (Nov 24, 2010)

slinger58 said:


> Just curious, is that because of airborne ash/soot?


'zactly. In some homes, it's bad enough that we can see where the GWB fasteners are.


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## hammerhead (Feb 18, 2014)

smokers or candle burners


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## slinger58 (Feb 11, 2013)

Gough said:


> 'zactly. In some homes, it's bad enough that we can see where the GWB fasteners are.


Due to the more conductive metal vs. wood, I assume. Amazing stuff.

What accounts for the cooler temps in the corner in the pic?


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## Gough (Nov 24, 2010)

hammerhead said:


> smokers or candle burners


Thanks, I totally forgot about them. It's been so long since we had clients that were either that it slipped my mind.


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## Gough (Nov 24, 2010)

slinger58 said:


> Due to the more conductive metal vs. wood, I assume. Amazing stuff.
> 
> What accounts for the cooler temps in the corner in the pic?


Typically extra framing or the lack of air movement ( boundary-layer effect).

We bought four thermal imagers a few years ago. Handy tools and fascinating to use. There are now some thermal imaging attachments for smart phones that make the technology a lot more accessible.


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## NACE (May 16, 2008)

hammerhead said:


> smokers or candle burners


And forced hot air oil heat.


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## CApainter (Jun 29, 2007)

Gough said:


> Typically extra framing or the lack of air movement ( boundary-layer effect).
> 
> We bought four thermal imagers a few years ago. Handy tools and fascinating to use. There are now some thermal imaging attachments for smart phones that make the technology a lot more accessible.


We are looking to purchase at least one of those this year. Apparently, they serve to identify excessive loads on electrical conductors.


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## Gough (Nov 24, 2010)

CApainter said:


> We are looking to purchase at least one of those this year. Apparently, they serve to identify excessive loads on electrical conductors.


All kinds of things that result in temperature differences: water leaks, settled insulation, where the dog has been sleeping....


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## PACman (Oct 24, 2014)

Gough said:


> All kinds of things that result in temperature differences: water leaks, settled insulation, where the dog has been sleeping....


...who really farted. it works!


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## Pete Martin the Painter (Nov 8, 2012)

CApainter said:


> Great feedback guys! It looks like it may be a combination of what you've explained. I certainly get the radiant cold issue and the lack of ventilation.
> 
> It seems like this may be a tough one to guarantee without some reconstruction.
> 
> Thanks!


I had this happen with a ceiling. And once I learned the probable cause (ghosting), I rewrote the contract that specified that I would not guarantee the ceiling. HO sdid not have a problem with it.


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## Gough (Nov 24, 2010)

NACE said:


> And forced hot air oil heat.


Forced air in general exacerbates the problem because of blowing household dust. If you're having a problem with ghosting because of soot, you have much bigger problems than ghosting, like CO poisoning. Combustion air and circulated air should be separate. If they're not, that most likely means a cracked heat exchanger.


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## CApainter (Jun 29, 2007)

Pete the Painter said:


> I had this happen with a ceiling. And once I learned the probable cause (ghosting), I rewrote the contract that specified that I would not guarantee the ceiling. HO sdid not have a problem with it.


As I mentioned earlier, about seven years ago I painted over a similar situation with one coat of BM regal Pearl. Not one bit of ghosting occurred. That's why it's puzzling to me. And I have only seen this with metal framing. 

I'm also wondering if the higher sheen prevents this from occuring.


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## PACman (Oct 24, 2014)

CApainter said:


> As I mentioned earlier, about seven years ago I painted over a similar situation with one coat of BM regal Pearl. Not one bit of ghosting occurred. That's why it's puzzling to me. And I have only seen this with metal framing.
> 
> I'm also wondering if the higher sheen prevents this from occuring.


A higher volume of resin solids in the paint helps quite a bit. Another reason to be cognizant of the actual quality of the paint. Cheap paints, specifically flats, are much more prone to this. (there! I can make a product post without bashing SW or Behr!) (DAMN! I did it didn't I?)


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## Gough (Nov 24, 2010)

CApainter said:


> As I mentioned earlier, about seven years ago I painted over a similar situation with one coat of BM regal Pearl. Not one bit of ghosting occurred. That's why it's puzzling to me. And I have only seen this with metal framing.
> 
> I'm also wondering if the higher sheen prevents this from occuring.


Have you always worked in the Bay Area? That might explain why you've only seen ghosting with metal framing. The temperature difference with wood-framed walls in more moderate climates is probably low enough to eliminate the problem.

I think the difference with higher sheens may reflect the difference in "stickiness" of flat versus pearl. At the microscopic scale, the flats are rougher and more likely to catch dust/soot particles.


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## PACman (Oct 24, 2014)

Gough said:


> Have you always worked in the Bay Area? That might explain why you've only seen ghosting with metal framing. The temperature difference with wood-framed walls in more moderate climates is probably low enough to eliminate the problem.
> 
> I think the difference with higher sheens may reflect the difference in "stickiness" of flat versus pearl. At the microscopic scale, the flats are rougher and more likely to catch dust/soot particles.


AND, the cheap stuff is the roughest and has less of any sealing properties. A perfect storm in certain climates.


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## CApainter (Jun 29, 2007)

Gough said:


> Have you always worked in the Bay Area? That might explain why you've only seen ghosting with metal framing. The temperature difference with wood-framed walls in more moderate climates is probably low enough to eliminate the problem.
> 
> I think the difference with higher sheens may reflect the difference in "stickiness" of flat versus pearl. At the microscopic scale, the flats are rougher and more likely to catch dust/soot particles.


I _have_ only worked in the Bay Area. Except for a few stints in Monterey, Yosemite, and Nevada. Your explanation makes sense.


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## CApainter (Jun 29, 2007)

PACman said:


> AND, the cheap stuff is the roughest and has less of any sealing properties. A perfect storm in certain climates.


I'll take the lateral pass I believe the original paint was spec'd for SW Promar 200. Majin Dat!


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## PACman (Oct 24, 2014)

CApainter said:


> I'll take the lateral pass I believe the original paint was spec'd for SW Promar 200. Majin Dat!


What? You're kidding right?


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## PACman (Oct 24, 2014)

I'm reminded of a time, standing at the end of a 200 foot hallway at the Bentree Nursing home with a SW tech rep, looking at the lovely reflection of the afternoon sun off the new linoleum floor, and wondering why after two coats of eggshell Promar 200 on bare drywall we could see every tape joint, patch, touch-up, and stud ghosting all the way down that 200 foot hallway. 

so we went to the other three hallways.....and when the light was juuuuust right, we could see every tape joint,patch,touch-up, and stud on every foot of them too.

This was PM 200 eggshell Dover white, two coats sprayed AND backrolled on bare drywall with no primer.

So the painter put another coat on using $8 a gallon Old Quacker eggshell and we never heard from him again. Funny how that works huh?


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## matt19422 (Oct 2, 2009)

Candle soot... seen it many times. Soot sticks to stud lines usually from no vapor barrier or moisture problem.


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## pacific paint (Nov 21, 2015)

Candle wax causes a lot of problems that are hard to detect.
Not sure that was the problem here, could be an explanation.

A candle melts away and the wax goes right on the walls, trim and doors.
More of a problem on doors when painting.


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## PACman (Oct 24, 2014)

PACman said:


> I'm reminded of a time, standing at the end of a 200 foot hallway at the Bentree Nursing home with a SW tech rep, looking at the lovely reflection of the afternoon sun off the new linoleum floor, and wondering why after two coats of eggshell Promar 200 on bare drywall we could see every tape joint, patch, touch-up, and stud ghosting all the way down that 200 foot hallway.
> 
> so we went to the other three hallways.....and when the light was juuuuust right, we could see every tape joint,patch,touch-up, and stud on every foot of them too.
> 
> ...


 Awww, what good times! You wouldn't believe how much I miss having customers scream at me like that painter did.


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## Gough (Nov 24, 2010)

matt19422 said:


> Candle soot... seen it many times. Soot sticks to stud lines usually from no vapor barrier or moisture problem.


A missing vapor barrier isn't the issue. The studs are cold and the moisture condensing on the GWB is from inside the building.


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## CApainter (Jun 29, 2007)

Gough said:


> A missing vapor barrier isn't the issue. The studs are cold and the moisture condensing on the GWB is from inside the building.


And since a combustion source is not the problem for the airborne contaminates, the ghosting must be occurring from poor filtration in the HVAC units. It sure is evident on the supply air registers.

Good stuff! Thanks again people! I'll explain the phenomenon to the occupants as if I'm a real expert on the subject. I apologize in advance that I won't be sourcing PT. I only have so much I can provide these days. They're already on to me


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## stelzerpaintinginc. (May 9, 2012)

Really good info on this thread. Thanks for the post CA and thanks to all who contributed. I had to subscribe. Gough's thermal imaging pic was icing on the cake.


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