Science of Evaporation - General & Personal Questions

[kyphysics]

Wasn't sure where to categorize this thread, but thought chemistry would be the most appropriate (mods: feel free to move as you see fit).

I have some questions on the science of water evaporation - first in general terms and then within the context of something that happened to me.
General Questions:
If there is water in liquid form, is the basic science/cause of evaporation (the water transforming into a gas) heat and/or air flow? Obviously, after it rains, water on the ground will evaporate over time and it seems to do so faster if the sun is out. What about the effects (if any) of air flow. For example, if you had rain droplets on the ground after a light shower/sprinkle and there was high wind, would that also cause or speed up the process of evaporation?

And, lastly, is there some temperature threshold for which water can or cannot evaporate?

Specific & Personalized Questions:
I had a repair guy discover a moist/damp area of exterior wall sheathing behind the vinyl siding of my house. For those not familiar with housing wall layers, you have - starting from the interior to exterior:

drywall (interior - basically this is what you see when you're inside your home) --> insulation and studs (in between the interior drywall and exterior sheathing & siding) --> sheathing ---> exterior home siding (be it brick, wood, vinyl or what have you)

The main posited cause (there could be others, but this is the immediate culprit) is several relatively small nail-sized (the width - NOT the length) holes left behind by a lamp installation contractor a month ago, who did not seal them up (he should have caulked them). Those holes penetrated through the vinyl and through the sheathing entirely, b/c they were nail and screw holes. Over the course of that month (after he left those holes), we've had rain maybe twice a week (some downpours being very heavy and windy).

The wet area of sheathing (that was immediately seen/felt - we did not unfortunately try to look further) was about the size of half a loaf of bread. It's unclear if the insulation behind it was wet or not (it was not checked***). And it's unclear if other areas of sheathing were wet as well. Only the immediate "hole" he opened up where the lamp was installed was seen. That hole size was about the size of a loaf of bread (I have pictures if that helps).

Anyhow, the repair guy said the dampness wasn't too bad and felt it was safe to seal up the vinyl area. I asked if it was really okay (having doubts about whether it could dry in a sealed up environment) and he said he believed so. Note: he was an electrician, so it's unclear if he was qualified to say this.

Questions (A): Given the science of evaporation, could a slight to moderately damp piece of material (in this case wall sheathing - if you don't know what it's like, ours was like a piece of cork board - those boards that you put pins in) dry out in a sealed up environment (i.e., inside a wall cavity)? After the repair guy left, I started second guessing his decision-making and thinking about possible mold growth.

Questions (B): This is just for pure curiosity and educational fun. Suppose I had a completely sealed glass jar - meaning no air flow - and it's 12 inches tall and 6 inches wide. Inside of it, I have a small layer of water - 1 mm deep and the full 6 inches wide. Would that 1 mm of water thin out or completely evaporate over time in that sealed condition? You can assume it's at room temperature too. I feel like a random case like this would also help me understand QA's possibilities too (and it's just independently interesting to ask/ponder).

Appreciate any responses/feedback you all can offer.

***at least not with touch, the repair guy said it just looked dry (visually - which I'm not sure is reliable, esp. in a dark space)

 

[Borek]

I would start with reading about the liquid/vapor equilibrium and its temperature dependece. Saturated vapor, dew point, such things, they make a good starting point to understand what is going on and what is possible.

In the end these are equilibrium processes with unknown kinetics, so while technically it is often reasonably easy to predict the final state, finding out how long it will take the system to get there is much, much more difficult, to the point were it is typically easier to measure than calculate.

Edit: note that "sealed" in the context of building doesn't actually mean water is not lost. Every air space is connected so there is always some minute air circulation (and diffusion through materials) that is perfectly enough for water to dry out. It is just a matter of how long it takes.

 

[kyphysics]

additional point: that damp sheathing was identified 4 days after it last rained, so it could have been even more wet prior to discovery

 

[kyphysics]

Edit: note that "sealed" in the context of building doesn't actually mean water is not lost. Every air space is connected so there is always some minute air circulation (and diffusion through materials) that is perfectly enough for water to dry out. It is just a matter of how long it takes.

Thanks for the full re: I'll check out those concepts when I can.

A random thought/question I had while reading your post: What about a sealed jar of OJ? Does the surface layer of OJ evaporate into the small air space at the top over time (say 10 years)?

 

[Borek]

Sealed jar case is what you will be able to answer by yourself once you get concepts I listed

(Edit: it requires some math and some data checking, but is in general not that difficult to calculate, with one problem: you need to know partial pressure of water in the air at the time jar was closed).

 

[jrmichler]

Questions (A): Given the science of evaporation, could a slight to moderately damp piece of material (in this case wall sheathing - if you don't know what it's like, ours was like a piece of cork board - those boards that you put pins in) dry out in a sealed up environment (i.e., inside a wall cavity)? After the repair guy left, I started second guessing his decision-making and thinking about possible mold growth.

Short answer: Yes, no, or maybe, depending on the construction of the complete wall assembly.

Long answer: Spend some time surfing this site: https://buildingscience.com/. They have a lot of information on moisture flow in walls. Moisture can get into walls from the inside or outside, and walls can dry to the inside or outside, or not dry at all. A more complete answer is far beyond the scope of a few forum posts, but that web site will completely answer your question.

 

[kyphysics]

Short answer: Yes, no, or maybe, depending on the construction of the complete wall assembly.

Long answer: Spend some time surfing this site: https://buildingscience.com/. They have a lot of information on moisture flow in walls. Moisture can get into walls from the inside or outside, and walls can dry to the inside or outside, or not dry at all. A more complete answer is far beyond the scope of a few forum posts, but that web site will completely answer your question.

Thanks, I actually will check it out too. On the personal/practical side, I also called my insurance company and local water damage/mold companies, who said (aggregated answers):
a.) it depends
b.) on? .....the amount of water soaked into your sheathing (or elsewhere) primarily and house construction secondarily
c.) the best solution is to probably do an on-site assessment (which I've set up for next week) to have experts SEE the condition things are in and they can even tear out a tiny piece of wall or exterior siding to peak inside (this is a low cost solution vs. like tearing down a whole side of house wall) to gauge/deduce conditions
d.) trusting a non-trained water damage/mold person (i.e., the repair guy) isn't reliable, b/c you need people licensed and trained in this area

So, on the practical side of things, there are TRAINED professionals who deal specifically with this...One offered me a free assessment and the other offered a paid one.

I'll report back what they say after they review things on-site!

 

[berkeman]

(I have pictures if that helps)

Pictures would be helpful, at least for me. Are there any openings in the interior drywall through which you could access that space or near to it? Like openings for AC wall outlets, wall switches, vents, etc.? If there are, you might be able to insert some small packets of desiccant into that interior space to help speed the drying process.

 

[kyphysics]

Pictures would be helpful, at least for me. Are there any openings in the interior drywall through which you could access that space or near to it? Like openings for AC wall outlets, wall switches, vents, etc.? If there are, you might be able to insert some small packets of desiccant into that interior space to help speed the drying process.

Sure, here is one that shows the vinyl siding cut open with the wet sheathing material (the black stuff on left)...it's black on top (maybe paint), but yellow/brown-ish behind it. . .and then "deeper" into that wall cavity you can maybe faintly see some yellow insulation (probably blurry). We dunno if insulation got wet or not, but that sheathing was mushy and damp.

I'm in between calls with lots of ppl still talking just about this subject, so I can post more later, but this was just a quick pic for understanding. As for "openings in the wall," yeah we do have some outlets and a clothes dryer duct, but I'm not super confident about "doing stuff" around those to not damage things if you know what I mean.

 

[Tom.G]

That wiring looks suspicious for U.S. standards. Any idea what that Brown wire is for?

From the absence of weather proofing around that hole, I would suggest using a different contractor for the next project.

Cheers,
Tom

 

[JT Smith]

I had similar concerns once when we had handyman repair a broken tile in our shower. Moisture had most certainly managed to get behind into the wall and after he repaired the tile I wondered if it would result in mold/mildew/rot.

I guess I'll never know because it's inside the wall. :-)

The sealed bottle thing is a much simpler problem. Basically you get an equilibrium of liquid water and water vapor where the amounts of each depend on the details. High school physics.

 

[BillTre]

Moisture had most certainly managed to get behind into the wall and after he repaired the tile I wondered if it would result in mold/mildew/rot.

I guess I'll never know because it's inside the wall. :-)

When remodelling a fish room (warm and humid with a history of a lot of water getting everywhere) we found mold behind the walls in some places. In subsequent discussions, the campus EHS (Environmental Health and Safety) people said that if mold (or asbestos) where suspected to be somewhere, their optimal solution would be to leave it alone if it was well sealed up.

 

[kyphysics]

I had similar concerns once when we had handyman repair a broken tile in our shower. Moisture had most certainly managed to get behind into the wall and after he repaired the tile I wondered if it would result in mold/mildew/rot.

I guess I'll never know because it's inside the wall. :-)

One of the water damage/mold/restoration companies I'm working with said they plan to poke a small hole in the drywall and/or vinyl siding and thread a "snake camera" in between the walls. This allows them to see inside without having to tear out large swaths of wall.

Perhaps in you situation, such a move can be done too?

This is standard practice, because it's cheap (Home Depot's 10 foot x 2.5 foot drywall is $10.99 a sheet...but the labor to put it up might be expensive.....but still just "construction worker" wages so not that bad) vs. tearing out the entire wall to inspect behind it.

 

[kyphysics]

That wiring looks suspicious for U.S. standards. Any idea what that Brown wire is for?

From the absence of weather proofing around that hole, I would suggest using a different contractor for the next project.

Not an electrician, so dunno about brown wire. Re: weather proofing. IT IS that silver/aluminum foil looking stuff, that degraded I guess over time. You see it on the right side a bit and perhaps the wet sheathing on the left made it slide off? . . .It's not contemporary standard (it was used 30+ years ago in building homes), which has more of a traditional vapor barrier behind vinyl siding. . . .In the old days, I'm told, they used that weird silver-ish looking thin layer.....which does look cheap and like it'd crumble JUST like aluminum foil LOL.

 

[hutchphd]

Any idea what that Brown wire is for?

I think that may be old tarnished bare copper ground wire. If so then wiring is not suspect but I'll bet it has been intermittantly wet for some time.
If you put a box there seal around the top and sides but leave the bottom open for a while. This is how it should have been done originally IMHO

 

[gmax137]

I think that may be old tarnished bare copper ground wire.

That's what I think too.

 

[JT Smith]

One of the water damage/mold/restoration companies I'm working with said they plan to poke a small hole in the drywall and/or vinyl siding and thread a "snake camera" in between the walls. This allows them to see inside without having to tear out large swaths of wall.

Perhaps in you situation, such a move can be done too?

I'm not opening up that Pandora's box. Until it makes itself known there's no problem as far as I'm concerned.

 

[hutchphd]

Unfortunately, given the legal stipulations if you have knowledge of mold, that may be the smart attitude. Personally I would want to know and remediate as necessary.

 

[kyphysics]

Unfortunately, given the legal stipulations if you have knowledge of mold, that may be the smart attitude. Personally I would want to know and remediate as necessary.

For clarification, is it the case that if a homeowner knows they have mold, then must remediate it and/or disclose it (to a potential buyer), but that if they don't know for sure, then they don't have to say anything.

Suppose a person suspects they could have mold, but doesn't know for sure. . . .Is that seller required to let the buyer know they might have mold in x/y/z spot?

 

[kyphysics]

I'm not opening up that Pandora's box. Until it makes itself known there's no problem as far as I'm concerned.

I guess in terms of probabilities and risk, I'd think if there was a known high probability of mold (I'm not saying your situation is like that), then the risk would be it spreading further and causing much more damage (physically and financially) later down the line.

Aside from the physical housing damage, it could cause severe health problems.

In my case, the damp wall (that my electrician may have errantly sealed) was very recently known to me, so it's something I can potentially stop in its tracks right away. Your situation is tougher. If your case happened like years ago, then it's hard to tell and it's maybe reasonable to think things have dried already.

 

[JT Smith]

I guess in terms of probabilities and risk, I'd think if there was a known high probability of mold (I'm not saying your situation is like that), then the risk would be it spreading further and causing much more damage (physically and financially) later down the line.

There is no external evidence of a problem. If there were mold inside a semi-sealed wall how is that going to affect my health? Even if correcting a mold issue isn't an extensive process by Pandora's box what I mean is that there may be other issues within that wall. By opening it up we might then feel compelled to replace studs that show sign of dry rot. Maybe the plumbing the incompetent contractor installed years ago has been slowly leaking. Perhaps the 90 year old wiring is substandard. It's like peeling back a piece of loose paint. You think it's a tiny blemish but next thing you know you're repainting the room, the halls, and the kitchen too. Maybe we should demolish the entire house?

 

[hutchphd]

This exactly mirrors my natural inclination regarding routine medical exams.
I fight these natural inclinations at every turn. Knowledge is power.

 

[JT Smith]

Guilty as charged to sticking my head in the sand. But I don't think it's the wrong choice in this particular instance. "Knowledge is power" is a cliché, not that it's wrong, just that it isn't always true. "Ignorance is bliss" is another one.

Maybe some math is needed:

Knowledge = Power
Money = Root of All Evil
Money = Power
Hence,
Knowledge = Root of All Evil

Best not to look sometimes. :-)

 

[hutchphd]

Ray Charles is (was) blind
Love is blind
God is Love
Ray Charles is God.