Moisture level in concrete slab 2

[dylansdad]

I have a 31,000 sf concrete slab placed mid September to mid October in 2021. I an unaware when the roof structure was installed and it was finally covered.
It is 8" thick slab underlain with 15 mil poly vapor barrier and 4" gravel.
It will receive a bead blast and an epoxy coating in an aircraft hangar facility.
The problem is the moisture (I guess Rh is the better word) levels are running anywhere from 89%-94% and the specifications require 72% for placement of the epoxy floor.
We are overall CM for the project and the subcontractor is of course saying we are "holding him up" by not allowing him to proceed with his covering.
I understand there are materials that can be applied to alleviate this problem, but we do not want to go this route ($) or sign any type of waiver/release for him to proceed.
We have been running the air conditioning at 72 degrees (we are in MS, high relative humidities here) for several weeks, but this has not helped.
Does this group have any other suggestions for "drying" this floor other than to wait it out?
Thanks in advance.

 

[MotorCity]

Turn off the air conditioning and crank up the heat?

 

[LittleWheels]

Wouldn't you use dehumidifiers if the building is enclosed? AC may or may not reduce slab humidity, depending on the AC system and the environment.

https://www.wagnermeters.com/concre...te-info/dehumidification-and-drying-concrete/

might be a useful read.

 

[dylansdad]

Thanks for the responses and the link.

 

[EngineeringEric]

you may want to have the epoxy rep meet you. the project is big enough they will. I'd find it hard to believe the ambient room temparture or RH effects the vapor transmission and moisture content of the slab much, but i don't know your site.

You also could hire a forensic engineer and get legit response

 

[EdStainless]

You would be better off with a hot building and dehumifiers. Most AC systems are designed to limit the amount of moisture that they remove.

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P.E. Metallurgy, consulting work welcomed

 

[dylansdad]

Eric/Ed, thanks for your responses.

 

[XR250]

Most AC systems are designed to limit the amount of moisture that they remove.

I have never heard of this. Can you elaborate?

 

[EdStainless]

AC is optimized for chilling air, so they tend to use high air flow across the coils in order to improve overall heat transfer.
In a dehumidifier the air flow is much lower to allow for more sub-cooling and time for droplet formation.
This also results in fully wet coils which have lower heat transfer values.
Most dehumidifiers also simply reject all of the heat into the space that they are drying.
You can do this with an AC system running the air handler on low speed, sort of.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[epoxybot]

EngineeringEric is correct about contacting the manufacturer. The problems with high relative humidity and epoxy coatings have to do with how they react with the humid air and surface finish. The surface can take on an "Amine Blush", leaving a dull surface. It often has a greasy exudate that needs to be removed with a wash. The final surface will be dull and have reduced performance to abrasion and chemical resistance. Another problem, is that some formulations accelerate when humid air is mixed into the coating during..., mixing.

Amine blush is nothing new to epoxy formulators and some products perform better than others. There a good water-based epoxies that might handle the atmospheric moisture better and still deliver Airport Hanger Grade performance. You just may have to shop a different manufacturer and add a small amount to the project.

 

[XR250]

Thanks Ed

 

[dik]

True with most coating systems including paints... that's why most coatings other than a gloss have a reduced life expectancy.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik