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Ambient humidity vs. RH

#1
Hi all. First time on the thread. I'm involved in the timber flooring industry down here in Australia (pronounced: Oz-stray-ya), where our standards are yet to catch up to the US. Subsequently, RH moisture testing is a very under-utilized practice at the moment. I look forward to joining the discussions here.

Question, and apologies if it has been asked a million times: I note the instructional video on temperatures having little effect on the RH of the slab. What about the ambient humidity of the area?

A major adhesives manufacturer rep mentioned to me that the highest number of moisture-related flooring failures occurred in a state which is known for its hot, dry climate. This is particularly telling as this area is a much smaller market than the eastern states, with areas known for their higher humidity.

Pardon my ignorance, does this imply that the inherent slab moisture (roughly the same in all locations, give or take differing mixing techniques between concrete layers) will translate to greater RH at the floor covering area, when exposed to a drier hot climate, as opposed to a more humid environment?

Or should it mean that the RH of the slab in a drier, hotter area will decrease more quickly?

Cheers
Pat of Oz
The problem with socialism is that you soon run out of other people's money.
- Margaret Thatcher

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#2
G'Day Mate!!!

Always nice to meet a new fellow from the land of roos. Glad you posted, please pull up a chair, grab a cup of coffee and enjoy! Smile

Concrete and moisture. Let's step back and take a look at the big picture before we get into details. It's really not as mysterious as some folks think it is, you just have to look at what is happening.

When concrete is poured in place, it has a lot of extra water in the mix that helps the workers put it in place and finish it. Even at a low water / cement ratio of .45, the concrete has twice as much water as it will ever need to fully hydrate. So what we have with all concrete slabs is a tendency for moisture in the concrete to want to come out of the concrete allowing the slab to equilibrate with its environment.

Now here's where the environment plays a role. A slab that is poured under water (bridge columns for instance) will not tend to emit water vapor (technically they could due to the heat of the cement reaction, but let's keep this simple for now). The underwater concrete piers are in equilibrium with their underwater environment when they are extremely wet.

A slab poured on a raised deck in the sahara desert where the average humidity is between 3% and 30% will emit water vapor until it is in equilibrium with the environment there.

Concrete poured in more hospitable living climates will tend to equilibrate somewhere around 50% -75% relative humidity.

The amount of moisture in a slab and its predisposition to absorb or emit moisture to equilibrate with the environment varies based on just a few factors. The RH of the slab and the RH of the environment. And of course these two factors change constantly, not just seasonally, but daily, even hourly. Now we can factor in moisture from the ground that slowly moves into the slab, slab porosity, floor covering porosity, temperature variations, I think the list of influences is quite long, but I don't need to worry about all that. Let the scientists work on the technicalities, let us keep our eye on the big picture.

So to answer your question, I would tell you that a slab poured in a drier climate will obviously dry faster than one poured in a damp location, but the slab in the dry climate is doing the same thing the damp climate slab is doing, they are both trying to equilibrate with their environment.
While the damp climate slab may be at equilibrium at 75% RH or 80% RH, the dry climate slab may need to be at a much lower RH before it reduces its push to rid itself of excess water.

Note: I almost said 'before the vapor loss is low enough to install a moisture sensitive floor' but I don't want to muddy that creek.... Here in Beaver Dam, we understand that even with a low vapor emission if we have a high RH pushing moisture, we have a high potential for failure.

And one more point if I may, when we say the temperature has little effect on the RH testing, we need to qualify that statement... put a little asterisk next to it...

RH, relative humidity, is a function of the amount of water in a sample of air and the temperature of the air. Obviously temperature will affect an RH reading. But the ambient temperature swings a room experiences will have little effect on the slab RH reading. What we have found in our area is that slabs poured on grade in a commercial facility generally stay at 67*F to 69*F. If I take an RH reading and my slab is at that temperature, I have a trusted reading, even if the room I'm in is being blasted by a heater temporarily and the air temp is 85.

On the other hand I have refused to allow installation on slabs that read 75% RH but they are very warm, say 85*F. This can happen in multi story structures where heat is being forced directly under the slab being tested. In those cases as the slab cools to the expected operating temperature of 72*F the RH reading will increase.

Sorry I'm so long winded... Tongue
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#3
Quote:A major adhesives manufacturer rep mentioned to me that the highest number of moisture-related flooring failures occurred in a state which is known for its hot, dry climate.

Thats where I live! It's allot like the Australian desert down here. I think he was talking about Arizona...aka arid-zone.
Stephen Perrera dba
Top Floor Installation Co.
http://www.tucsonazflooring.com
http://www.floorsavior.com
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#4
Don't apologise! The devil's in the details. Plus I've been enjoying your work as a spectator for some time, JD. Thanks for the response.

Perhaps I need to go back to school on the meteorology, but I think I understand these alleged failures in the drier climate, if I'm getting my head around it right.

a) Perhaps installers are taking RH readings (in the cases where they even bother) with a higher slab temperature. When the slab cools to what is, presumably, its normal "operating" temp the RH increases and thus the likelihood of a related failure.

b) Or, in your words "the dry climate slab may need to be at a much lower RH before it reduces its push to rid itself of excess water." because the environment's RH is naturally lower. ("push"= vapour emission). So it is emitting more flooring-unfriendly vapour for a longer period before equillibrium with the surroundings, if you'll excuse my child-like layman's terminology.

Should this mean that the required acceptable RH for our flooring neighbours out west where its drier and hotter, should be lower? Or have I still missed something? This is quite possible, as I am Australian, and we have only just graduated from Paul Hogan to Hugh Jackman as our chief ambassador.








(10-06-2011, 03:43 PM)Ernesto Wrote:  
Quote:A major adhesives manufacturer rep mentioned to me that the highest number of moisture-related flooring failures occurred in a state which is known for its hot, dry climate.

Thats where I live! It's allot like the Australian desert down here. I think he was talking about Arizona...aka arid-zone.

Funnily enough the town I was referring to, Adelaide, is "sister city" to Austin, TX. I grew up in Adelaide, and once applied for a job in Austin. No correlation between these two trivialities, nor with the fact that I totally want to come to Austin for that F1 race!

I'd believe that the South Oz climate is much more like Arizona, though. It's pretty hot and dry. Now I live in the eastern states where we have four seasons in one morning. Ugh.

The problem with socialism is that you soon run out of other people's money.
- Margaret Thatcher

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#5
(10-06-2011, 05:16 PM)Rubensgt40 Wrote:  I've been enjoying your work as a spectator for some time, JD. Thanks for the response.

Well it is quite obvious you are an extremely intelligent man Rubensgt40, by the way do you mind if I put your quote on a t-shirt that I can give to my compadres here on the forum?? Tongue

I believe you have the idea down pat already. Do you have any friends you could bring on the forum? Big Grin

As for regional differences in acceptable RH levels, I have not experienced such a thing. I do know that 75% is regarded as safe in the states, but I also know it is very safe in the areas I work. I haven't seen problems at 80% and probably never will. Maybe even 85% would work, but one must keep in mind that ignoring the manufacturer's recommended installation parameters will most likely void any warranty on the materials.
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#6
If you get t-shirts printed, send me one Tongue

We're in the process of tightening up the standards now. BTW we reference ASTM F2170 in ours (or we will, fairly soon). As I see happens in the US, the more the standards are refined, the more manufacturers get on board and write up their specs accordingly.

At the moment, we are still emerging from moisture content as the testing requirement and formally moving to RH. The hood method is catching on.

After studying this forum (and Wagner's products) that will have to change.
The problem with socialism is that you soon run out of other people's money.
- Margaret Thatcher

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#7
Pat,
How do you measure moisture content now?
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#8
(10-07-2011, 06:07 AM)CC Solutions Wrote:  Pat,
How do you measure moisture content now?

Good question! I am in the area of wholesale to the trade, installers and finishers of Timber flooring. I presume the bigger installers/ timber flooring shops use moisture meters. You wouldn't know it from my vantage point, because we haven't sold a meter in yonks. Having said that, it has never been our core business. That will change, and this is one of many reasons why I'm keen to catch up in the knowledge stakes.

Another, as I said above, is that the AU/NZ standards are moving to RH and improving generally. Bear in mind I'm talking about the Timber Flooring game specifically. General and resilient flooring has always had more active industry association standards etc. We're catching up.

I'd really like to pop over for the ICRI Cert, at least. I think the trade here are drastically behind.




The problem with socialism is that you soon run out of other people's money.
- Margaret Thatcher

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#9
I know of a New Zealander who just came over for the ICRI cert.

Have you ever heard or seen rh testing in lumber? I found a site that has pics of tiny sensors embedded in lumber. Kinda neat. I hear it is much more accurate than a pin meter.
Stephen Perrera dba
Top Floor Installation Co.
http://www.tucsonazflooring.com
http://www.floorsavior.com
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#10
(10-08-2011, 01:42 PM)Ernesto Wrote:  I know of a New Zealander who just came over for the ICRI cert.

Have you ever heard or seen rh testing in lumber? I found a site that has pics of tiny sensors embedded in lumber. Kinda neat. I hear it is much more accurate than a pin meter.

I know the Kiwi you're referring to. She's very busy now!

No, I haven't heard or seen that with lumber. With the wide range of applications for timber generally, I presume the technology that industry is more acute.

Obviously our customer base use timber moisture meters more, pins and resistance. But even then, we don't see many sold.
The problem with socialism is that you soon run out of other people's money.
- Margaret Thatcher

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