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Preparation of Concrete for Moisture Testing - is it REALLY necessary?
One of the most debated and controversial subjects regarding moisture testing, is the preparation of a concrete surface before testing.
Each side has its compelling reasons for testing or not testing...I am one of those who is a supporter of preparation, and am quite adamant about it.
Before the flooring contractor even steps onto the project, so much can happen to the concrete he isn't aware of, same goes for the testing/inspector and even the project managers themselves.
Here are photos of a project we were involved with several years ago, where, during the preparation, this nasty surprise surfaced..we stopped immediately, called the project manager and in the second photo, more area was ground..needless to say, the General Contractor was NOT happy! This condition repeated itself throughout most of the 600,000 s.f. of concrete scheduled for moisture sensitive flooring materials!
Each side has its compelling reasons for testing or not testing...I am one of those who is a supporter of preparation, and am quite adamant about it.
Before the flooring contractor even steps onto the project, so much can happen to the concrete he isn't aware of, same goes for the testing/inspector and even the project managers themselves.
Here are photos of a project we were involved with several years ago, where, during the preparation, this nasty surprise surfaced..we stopped immediately, called the project manager and in the second photo, more area was ground..needless to say, the General Contractor was NOT happy! This condition repeated itself throughout most of the 600,000 s.f. of concrete scheduled for moisture sensitive flooring materials!
Replies to This Discussion
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Permalink Reply by Stephen on -
Looks like thats an extreme situation there Bob. Is that a topping?
I still must respectfully disagree. On a regular ole slab you do the water drop test for sealers, no sealers go to cacl test on top of the surface you plan to adhere to. Otherwise if you grind the surface your getting a false reading than what your adhering to. Unless of course your going to grind down the entire floor.
For instance lets say you have a steel trowled surface, you get slower absorption of the water, still it does not bead up....much or as long. Then to be sure do a bond test.
Thats my compelling reason.
Now if I could only get this ring on my faucet to come off thats been on there for 25 years I'll be in a better mood! Ahhh! :)
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Permalink Reply by Bob Higgins on -
That is a "regular" concrete surface...finishing techniques (such as what was used in the photos) can hide a myriad of problems waiting to ambush the other trades....this was a "polished" surface, leading us to believe it was a good quality concrete....
The grinding removes foreign contaminants and removes what amount to an eggshell..revealing what the "egg" actually consists of!
Not grinding the concrete to reveal what the potential permeability is..is not much different than trying to identify the quality of steel reinforcement by using surface grading devices. Those were breifly popular in the mid to late 1980's when laboratory tests indicated that the amount of charge passed, was correlative to the amount of corrosion being experienced by the contained steel reinforcement. That came to a screeching halt when some researchers mapped a bridge in New York..opened an area that was supposedly suffering from "extreme corrosion" according to the device and found NO corrosion!!
The surface finish of concrete could also be likened to a coat of paint..hard to judge what condition the surface is until you remove the paint
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Permalink Reply by Stephen on
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Bob, so the part in the corner had been ground off (top pic) ? Thats amazing that the cracks did not go all the way to the surface, How much of the surface was taken off?
Another question...how would this effect any MVER if not ground off?
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Permalink Reply by Bob Higgins on
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In this project..the "skin" was very shallow, less than 1/64th of an inch. If you look VERY carefully, you can see hints of the cracks where the concrete had no yet been prepped.
Although no tests were taken prior to the grindiing...about a year before this project, I was asked to take a look at testing conducted on new concrete for a high tech facility. I was informed the moisture tests ranged from slightly over 5lbs to slightly over 9lbs, which seemed reasonable since the specified concrete was a 0.45 water-cement ratio.
When I inspected the facility, NONE of the tests were conducted over concrete "properly" prepped...the curing compound was still on there..and here is where I caution people, there was no obvious "beading" of the water. Some acrylic-based curing compounds do not "bead water" since they are not designed to be water repellent, and some of the so-called "dissipating" curing compounds will NOT dissipate unless exposed to direct sunlight.
To make a long story short, once the surface was ground, very few results were under 15lbs!!! Since these numbers didn't correlate with a low water-cement ratio, we reccomended the owner have a petrographic analysis be done..the concrete averaged a 0.62 - 0.65 water-cement ratio! Suffice it to say...the flooring contractor was VERY happy we had been there!!!
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Permalink Reply by Stephen on
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It's not abnormal to see cracks eminating from a central point going out in all different directions like the one in the corner.
What surprises me is the pattern of them in the second picture. I have never seen that in a slab with the exception of a few slab over slab pours for sunken livingrooms. Very weird indeed. But I would also say very rare in form.
OK, for now I will accept the fact that I need to prep, even though I feel I will get higher reading in both moisture levels and ph. But if those are within the zone I guess there is nothing to worry about....untill the next day. lol
This gives lots of creedence to why one should float a floor rather than glue one to concrete.
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Permalink Reply by Bob Higgins on
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Stephen..yoyu brought up an exceptionally good point...with the advent of water-based adhesives, which adds a "clean" water to an alkaline surface (concrete), and that cement is now more alkaline that in the past (EPA regulations have caused the cement producers to recover flue gases, reincorporated into the cement, increasing the alkalinity content by as much as 400% compared with cement prior to the year 2001)
Adhesives that are 100% solids would/should have less concern..it would be interesting to see if the manufacturers of these adhesives have been developing any statistics on this!
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Permalink Reply by Stephen on
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Just wanted to make sure ppl here read this other forum if you have any dealings with concrete and mositure testing. Some really good debates going on here and great info.
http://www.wagnermeters.com/concreteforum/moisture-measurement-in-c...
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Permalink Reply by Stephen on
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A little tidbit I found in some lit:
302.2R-18 ACI COMMITTEE REPORT
"shown that the adhesive strength decreases with an increase
in the concrete’s MVER. When these tests were conducted,
however, there were no criteria for acceptable bond strength,
and scatter in the test results did not indicate a clear dividing line
between acceptable and nonacceptable adhesive bond strength.
A report on recent testing that attempted to correlate moisture
in the concrete with floor covering performance concluded
that: “The evidence presented suggests that there is no
relationship between the relative humidity of a concrete base
or screed and adhesion of resilient floor coverings” (The
Concrete Society 2004).
While moisture criteria are often used, the relationship
between these criteria and floor covering performance is not
well understood."
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Created by Steve Simonson Nov 6, 2008 at 10:58am. Last updated by Steve Simonson Nov 6, 2008.
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