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Discussion Starter · #1 ·
5 yrs ago I remodeled my empty attic in my 1927 bungalow. I had closed cell insulation foarm sprayed between the studs and the rafters all the way from the ceiling peak to the bottom of the roof (roof overhang/soffet/facia). I built knee walls. I put 1" rigid foam insulation onto the studs and rafters of end walls, built out ceiling, slanted ceilings/walls and also on the living space side of the knee walls. I red taped all the rigid foam seams. I put drywall on the inside of all the rigid foam and used black drywall screws that were long enough to anchor the sheetrock well.
Now, almost overnight fuzzy dark grey spots appeared on the painted sheetrock where each of the sheetrock screws are on all the exterior walls, including the knee walls in the well heater central area and the cool closets, but not on any built out inside walls.
The spot color does not wipe off. When I use a sharp object and scratch the spot slowly to look for layers, the mud over the screws is the same color all the way from screw to surface. The screw does not look corroded at all and nothing wipes off it.
I hope you can shed some light on this, and perhaps what to do.
 

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My wild guess? Cold screws and condensation is starting to corode the heads of the screws----

Have you experienced some unusually cold weather this year?

A solution is likely this---a new paint job---to add a vapor barrier.


Check the settings on your humidifier----
 

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What you're seeing is one of the few instances of Quantum Mechanics at work in real life. Those dark marks over the drywall screw heads are a combination of dirt and soot from smoking cigarettes and/or burning candles or incense.

In Newtonian physics, if you bounce a ball against a wall, the temperature of the wall doesn't matter; the ball bounces off the wall and back to you regardless of how hot or cold the wall is. In quantum mechanics, as the ball gets smaller and smaller and smaller, the kinetic energy of the ball increases or decreases as a result of it bouncing off a warm or cold wall. In this case, the extremely fine particles of soot are small enough that their energy is entirely lost as a result of coming into contact with a cold surface. In this case, the coldest surface on your walls and ceilings are the spots directly over your drywall screws because metal conducts heat very much better than wood, drywall or insulation. So, the spots over your drywall screws are the coldest spots on your exterior walls, and so that's where tiny particles of soot collect.

Some people claim that the soot accumulates on those spots as a result of minute amounts of condensation forming over those spots. They claim that the soot sticks to the tiny amounts of liquid water at those locations. All you have to do is recognize that the surface tension of water is strong enough that you can float a razor blade or paper clip on the surface of water. In fact, many bugs are able to "walk" on water because they have 6 or 8 legs and and their weight is supported by the surface tension times 6 or 8. Something as tiny as a particle of soot wouldn't have enough energy to break that surface tension and become engulfed in the water. So, the particle of soot should simply bounce off the surface of the water instead of penetrating into it.

Your best bet at removing those spots is to use a damp Magic Eraser to clean them off.
 
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Discussion Starter · #4 ·
Hey guys thanks for your replies.
Last year was much colder than this year.
I have no humidifier on that floor.
The spots don't wipe off w a magic sponge (tho I love then).
The color is all the way thru the drywall and not just on the surface, and the raw uncovered screw heads don't seem to have any rust or other corrosion.
:grin:
 

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Discussion Starter · #5 ·
A trademan measured 60% and another 70% humidity in the space (attic). I probably sealed it too tight. So I'm guessing it's the humidity. 3 mold tradesmen said it wasn't mold for sure. Either there's some chemical interaction of the black sheetrock screws (am told I should've used zinc screws), with possibly a bad batch of nails, or the screws getting cold even though I insulated so well (the studs are not insulated on their exterior, just stucco) are attracting dust and candle smoke. One tradeswoman with the word Custom in her company's name, said I need a whole house fan in the roof. She said it would be good for the whole house (bungalow built in 1927 with new windows). She said it would be extremely quiet and would cost $700-1000. I have a few other tradesmen coming over tomorrow to get opions and bids from. Wish me luck.
 

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If your attic is sealed that tight she is right. An attic needs to breath that is why we vent it with soffit vents and ridge vents.
 

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Sounds like thermal bridging ->http://en.wikipedia.org/wiki/Thermal_bridge

Here's a snippet from the link above:
Thermal bridging is created when materials that are poor thermal insulators come into contact, allowing heat to flow through the path of least thermal resistance created, although nearby layers of material separated by airspace allow little heat transfer.
 

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Discussion Starter · #8 ·
Thanks Paul and ToolSeeker.
Any tips you can tell me about getting a whole house fan?
It may either go through a kneewall or through the attic ceiling (which would likely then have to span a space to the roof.
Thanks, Lisa
 

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A whole house fan sucks the warm air out of the living space and pushes it into the attic----very nice things as long as the attic has enough vents to exhaust that volume of air----you mentioned high humidity in the attic---so I'm sure that adding a roof vent (powered or convection) will be needed before you add a 'whole house' fan.
 

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A whole house fan is used for house ventilation not humidity control. The whole house goes in the ceiling and pulls air through open windows and pushes up through the attic and through the attic vents. You have to open most of the windos while it is running. I have one and use it in the summer instead of AC when it gets cool enough at night.

Sounds like your attic needs better venting . I would look at passive methods (soffit vents, gable vents, and or ridge vents). Your attic needs to be as close to the outside air temp as possible. If for some reasons passive vents won't work then look at powered ventilators . But you will still need soffit vents for the air intakes.
 

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Antiwingnut:

No, you read my statement incorrectly.

It was supposed to be read as:

"What you're seeing is one of the few instances of Quantum Mechanics at work in real life that I can somewhat explain."

It appears that I merely overlooked including some of the words that were meant to be in that sentence.

Please try to be more careful in future.
 

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Seeing as quantum mechanics is used to explain sub atomic particles and the like, it doesn't seem applicable or correct to use it to explain something which is due to surface tension, convection and static electricity
 

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Welcome to Quantum Mechanics 101

Back in the 1890's, physicists were confident that they understood matter and energy. Atoms were understood to be particles of matter, and energy consisted of electromagnetic waves like light and heat.

One of the problem with this understanding of atoms as billiard balls and waves as energy was that it couldn't explain one of the most perplexing problems of the time, something known as "cavity radiation".

The problem of cavity radiation was that if you took ANY hollow solid object, drilled a hole through it's wall into the hollow interior, and then heated that object, the spectrum of the electromagnetic radiation that was emitted from the exterior of the object was dependant on both the temperature you heated the object to and the material the object was made of. That seemed to make perfect sense.

But, the spectrum of the radiation emitted from the hole in the object was solely dependant on the temperature, and was the same regardless of what material the object was made of.

WTF?

The radiation emitted from the hole originated at the interior surface of the body, which was exactly the same as the exterior surface of the body, so why would the spectrum of the radiation emitted from the hole be so uncharacteristically different?

At the time, a well established physicist by the name of Wilhelm Wiens was working on the problem of cavity radiation and was able to derive a theoretical equation based on the assumptions of atoms as particles and energy as waves that partially predicted cavity radiation at relatively low temperatures. The equation Wiens came up with was:

http://upload.wikimedia.org/math/3/5/e/35e692d3a95d53e219af39cabfe47021.png

And at the same time, a young Physicist in Germany named Max Planck was working with emperical formulae that predicted the spectrum of the radiation emitted from the cavity very precisely . These emperical formulae had no theoretical basis, but were simply equations generated which simply happened to match the results observed from laboratory measurements very accurately. The emperical equation Max Planck had was:

http://upload.wikimedia.org/math/d/e/4/de49247c3e38ac7ef9a3c713d822d308.png

Max Planck noticed that Wiens' theoretical equation bore a striking similarity to the emperical equations that he had been working with, and decided to try to work backward through Wiens' theoretical derivation using his emperical equation as a starting (er, ending) point to see if he could come up with a theoretically sound derivation of his emperical equation.

And, he found he could do it.

All he had to do was make the contentious assumption that the energy emitted from the cavity was "quantized", or in distinct individual packets. This is much like saying that you cannot have ANY amount of money in your wallet, only certain distinct quantized amounts. For example, you cannot have Pi dollars in your wallet. You can have #3.14 or you can have $3.15, but you cannot have $ Pi.

That is, if energy was money, Planck had discovered the penny.

Planck subsequently received the 1917 Nobel Prize in Physics for his discovery of the "Elemental Quanta", and this was the origin of the branch of physics we call "Quantum Mechanics".
http://upload.wikimedia.org/math/d/e/4/de49247c3e38ac7ef9a3c713d822d308.png
 

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I did not realize that drywall was so complicated. No wonder some guys charge so much to hang and finish it. They have to be PHD theoretical physicists. LOL
 
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