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insuti testing

#21
CC Magazine did a Concrete Curling Field Test.

In one store room they did a grid of many different finishes and they installed RH probes.

I can't find it online, it may have only been in the magazine, so I am going from memory that is a few years old. But, the result was marginal. There wasn't a statistically significant change in RH between different surface finishes.

However, I've heard this surface finish drying argument more and more. Our flooring manufacturer started saying it quite a bit. I worry because I do not think any studies have backed up the assertion. However, it is a nice one because it does put some of the 'why is the concrete still wet' blame back on the finisher.

http://www.concreteconstruction.net/on-the-job/cc-field-test.aspx

We have found in the past our contractors have hit slabs with an aggressive sanding disk or even a light beadblast and you can get CC test to drop quickly. However, I do not know about RH tests.
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#22
If the moisture is coming out of the concrete, the RH is going down.

Steel trowels seal concrete. That's what they do. That's why they are used.

Sealed concrete, either chemically sealed or mechanically sealed, will dry slower than porous concrete.

It works! Couple it with a 3 day wet cure and you have a great chance at having dry concrete when it's time to put the flooring down.
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#23
Steel trowels also make concrete flat.

The difficulty to make that slab flat goes way up if they can't machine it flat. Requires a lot more attention by designer and many of them do not have the skills. The answer from the 'industry' is to use type k cement. But that increases material costs bu 25%.
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#24
All the final trowel does is seal the concrete. The consolidation is done with mags and combo blades. By the time the steel blades are put on you can walk on the concrete.
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#25
So, consolidation creates flatness?

And the steel densifies the surface layer.

I learn something new every day. Love this forum!
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#26
(05-02-2013, 10:21 AM)eaadams Wrote:  So, consolidation creates flatness?

And the steel densifies the surface layer.

I learn something new every day. Love this forum!

Not exactly, but when concrete is poured it has voids in it and working the concrete works many of those voids out. While it is still plastic it can be moved around and shaped, including being 'flattened'.

Steel blades seal the surface and densify it. Much of this densification comes from the moisture being retained which then allows additional cement paste reaction.
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#27
I thought the top dark steel layer typically has lower cement hydration due to the water being pushed out.

ref: http://www.concreteconstruction.net/concrete/unexpected-results.aspx

" The process of squeezing most of the water and air voids out of the top 1/8-inch layer causes other changes too. Portland cement that doesn't hydrate soon after the initial mixing process doesn't hydrate in this layer either (see Photo D). "

[Image: tmp20.tmp_tcm45-627527.jpg]
"In this scanning electron microscope X45 magnification of the profile top ¼ in. of the slab unhydrated portland cement particles appear as white dots and air voids appear as black dots."
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#28
Incredible as they say TMI can confuse you. Have to figure out a way to index all this info. WOW!
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