Testing Cost - Printable Version
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RE: Testing Cost - CCR - 06-15-2012 05:48 AM
I remember that one too...fairly recent I believe.
Kinda proves my point about improper testing done out there by too many just trying to save a buck by not calling in qualified testing technicians. I've been immersed in this problem for almost 10 years now and firmly believe my contribution to all parties concerned on a jobsite has value.
RE: Testing Cost - CCR - 07-26-2012 08:36 AM
Anyone done any exterior RH testing on structural concrete being renovated for application of coating systems? Just finished placing Wagner Sensors on 40 year old, 5" slab and got readings from the mid 70s to mid 80s. It was 86 degrees and 68% relative humidity at 9 am (sweat my a#! off). I got a hunch they're going to climb. Previous coating had no problems, this work is just part of a complete renovation.
RE: Testing Cost - CC Solutions - 07-26-2012 08:49 AM
Exterior rH will fluctuate quite a bit. It will be lower at higher temps and higher at lower temps with the same moisture content. Look at a psychrometric chart for reference.
RE: Testing Cost - CCR - 07-26-2012 08:53 AM
RE: Testing Cost - CC Solutions - 07-26-2012 09:48 AM
Actually you need that 'r' in there or it relates to mental issues, which may not be completely improper when it comes to concrete drying...
A psychrometric chart displays the relationship between air, temp and moisture. Let's see if I can post one here....
Now using that chart it is quite easy to see your concrete is too wet....
Or too dry.... Or maybe it's too gray or hard.....
The chart looks confusing but really it is quite simple to use.
RE: Testing Cost - CCR - 07-26-2012 10:16 AM
Thanks! That's gonna take some major desipherin (sp?). But I'm sure I'll figure it out.
RE: Testing Cost - CC Solutions - 07-26-2012 10:54 AM
The curved lines going from lower left to upper right are the RH.
The vertical scale is moisture content in grains.
Horizontal scale is temperature in F.
Now here's an easy example. Let's say your air is 80 degrees and 60%RH. If you plot the 80 degrees by going to the right on the bottom of the chart to 80 and follow that line up, find where it intersects with the 60%RH curved line. Mark that point. Now if you go straight left or right you can see what the RH is at various temperatures.
At 75 degrees you will have 70%RH. At 100 degrees it would be 32%RH.
When you measure slab RH, you are measuring the relative humidity in the air in the bottom of the hole. While this sounds like a slam dunk for calculating the RH at any given temp if you know a starting temp, unfortunately it doesn't quite work that way.
I have tested slabs for months as they go through temperature swings and my numbers did not match the chart. Some of this may have to do with hysteresis, some may have to do with moisture suppression, or maybe it's something with moisture releasing from the concrete and reabsorption, I haven't studied the issue yet. Howard Kanare was rumored to be working on it so I'm sure not going to...
What I am getting at is you can't extrapolate that a slab at 80 degrees and 60%RH will read 90%RH at 68 degrees. While it works well in the atmosphere, it hasn't been working in the test hole.... This is also why it is important to take your readings under service conditions! If you say a slab is fine to put flooring on when it is at 80 degrees and 60%RH, then the building is cooled and running at 68 degree slab temp, you can bet your RH will NOT be at 60% in that slab. If you have a failure and someone tests after you at the lower temperature, they will get a higher reading.
I test at service conditions and use extrapolation very carefully. I'm sure Jason can jump in here and explain the relation between temp and humidity in the space read by the probes, and tell us if we have a method to extrapolate to different temperatures accurately yet.
RE: Testing Cost - CCR - 07-26-2012 12:57 PM
All makes sense. Obvious testing challenge with garages and concrete roofs (a previous thread), is that service conditions have a huge swing. Today was about as hot and steamy as we get here. Come January, it could be 0 degrees. The particular manufacturer of the coating system specifies ASTM 1869 for testing, which makes no sense to me (except for that's what everyone did for years). However, they also recognize RH testing now and accept readings of 80%. It would be great to get input from Jason on this subject. It would make for a very good article in the online newsletter.
I think the best thing for me to do is include my standard disclaimer about readings being accurate at time of test and future results may vary, etc., etc.
RE: Testing Cost - CC Solutions - 07-26-2012 02:36 PM
I'd ask the manufacturer 80% at what temperature???
Sounds like they haven't thought things through yet......
RE: Testing Cost - rapidrhrep - 07-27-2012 08:07 AM
@CCR-The interesting thing about the topic you bring up is that within a certain temp range (not sure what the range is) the concrete has a certain insulatory capacity, making ambient condition swings less impactful on RH readings at 40%. Notice I say LESS! In our webinar, Howard actually alludes to information that is being reviewed that may allow for a correction factor, taking into account ambient conditions. The interesting thing about the whole topic is that you have exterior products, like garage floors and roofing material, that are specifying F2170 already. They are experiencing the same problems as the flooring industry. I do agree with CC that, at this point, I would grill the manufacturer on ambient condition requirements.