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**EXPERT Advice Needed** - VERY Moist Slab With LOTS of Vapor! What to do?

#1
Good evening,

My name is Luis, and it is a pleasure to make the acquaintance of anyone kind enough to assist me in this predicament. I am a lowly homeowner and I request the advice of the fine minds that roam through this forum.

I am dealing with a slab that is internally moist that is releasing the moisture in the form of vapor. To make a very long story short, we had a leak beneath the slab which caused the slab to become quite wet. The wet slab over a period of time created a substantial amount of water vapor, ultimately leading to my having to remove my beautiful large porcelain tile (with very thin grout joints).

Now, the slab has been open for approximately 3 months (with nothing on it but some thinset residue) but it remains quite moist. Although the slab appears dry to the naked eye, there is a substantial amount of vapor being released. The results of the multiple calcium chloride tests have been in the HIGH teens.

I have recently employed the use of two industrial size dehumidifiers and five drying fans which have been on for about two weeks. The dehumidifiers bring down the ambient humidity within the room to about 35% when they are on (otherwise it is usually 45% in the house with the a/c set at 72 degrees).

What I am seeing is that when using a handheld moisture meter (the type with the two prongs that you use on top of the slab), the moisture content has gone down significantly on the slab (the digital display on the meter has gone from the high 80's to the 30's) as measured by that device.

However, I was smart enough to have installed 5 separate Wagner Rapid RH 4.0 relative humidity sensors at different locations in the slab (within this area where the tile was removed). Each of these sensors are showing a relative humidity of 99%! This relative humidity has remained at 99% for the past three weeks, and unfortunately the dehumidifiers have not changed the RH at all. (The slab is 5" thick, so they were installed 2" down, as that is 40% of the thickness of the slab, per Wagner specifications). In addition, in areas where I have tried the old plastic taped to the slab test, I see discoloration (darkening) in the slab within 24 hours and moisture beads on the inside side of plastic within 48 hours.

BOTTOM LINE: My slab is still moist. The top layer of the slab has clearly dried a bit with the dehumidifiers and fans, but nothing is drying the middle/bottom of the slab AT ALL!

So, what should I do?

I would like to put some sort of coating or product on the slab now before I put a new floor down (the slab is obviously too moist to put any floor down). I am particularly interested in Ditra by Schluter systems. The reason for this is because I know that I am experiencing significant vapor issues that will likely continue, and Ditra will allow that vapor to channel away from the slab. Also, I love the idea that it is an uncoupling membrane.

In addition, I am also considering: (a) bead blasting the slab or (b) scarifying the slab, to release the locked-in moisture within the slab.

QUESTIONS:

(1) Do you recommend Ditra? For my problem, would you recommend Ditra, or instead a sealer like one by Ardex or Laticrete? My concern with those products is that they may "pop up" after a number of years during the time that the heavy vapor is being released.

(2) Is there an issue with using Ditra considering that there is so much vapor coming up? Particularly, will my walls/baseboards (where the vapor would be funneling to with the Ditra) become saturated with vapor and ultimately become wet and moldy? Is there so much vapor coming up that it will condense into water (like it did previously beneath my old tile) and channel under the tile within the Ditra to the walls?

(3) Do you recommend doing something (scarify, bead blast) to the slab now, before I put down the Ditra? The theory is: if I scarify or bead blast the slab, it will allow all of the excess moisture to be released from the slab before I put down the Ditra, especially if I keep the dehumidifiers and fans on after the scarification/bead blasting. Please note that right now there is a thin layer of residue thinset on the slab likely inhibiting the drying. On the other hand, will scarifying or bead blasting the slab cause issues in the future? To be more clear as to my concern: since I know there are vapor issues, will doing this to the slab allow more areas for the vapor to easily rise up through the slab and cause it to condense into water that much quicker?

(4) Is there any benefit to having a french drain created around the perimeter of the slab? I have heard of others doing this for vapor issues within the slab (usually if they have a grading issue), but I was not sure if there is any benefit for my purposes (i.e., does it aid the drying process of the slab?). I can't see how a french drain could help me, but I thought I would ask the experts!

Thank you for any help you can provide! I appreciate it!
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#2
It sounds like there is moisture diffusion from extraneous sources. Is there any knowledge to the source of the moisture? Have you contacted a geo technical expert to determine the source?
There are a lot of avenues to explore once the source is determined.
Regards
Rayt
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#3
I would definetely start with # 2 and 3 right away. You must keep more water from reaching that slabs perimeter. And the bead blasting will open up the surface for faster drying.

Let us know if the rh drops.
Stephen Perrera dba
Top Floor Installation Co.
http://www.tucsonazflooring.com
http://www.floorsavior.com
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#4
My first thought is that no matter what you do, the slab is subject to ground water and humidity because you do not have a great vapor retarder under the slab. While this may not be a problem if you can keep the surrounding area very dry and use a porous flooring, anything short of those two options is playing with fire.

You can mitigate the slab with several permanent products made for this situation. The process would be to bead blast the surface, apply the epoxy and then put down a primer so your thinset will bond to the epoxy.

Some of these mitigation systems you can buy yourself, and some you must be a certified installer to buy.

This is the way I would go, but that is what I do, mitigation systems. Big Grin
It is relatively easy, fast and permanent. I did not say cheap did I?? Tongue
As for pricing, you can expect to pay $1.50 to $2 a square foot for the epoxy. If you want to self-perform, you can rent a bead blaster for $400 a day or hire someone to blast for you (highly recommended). Expect to pay around $2 per square foot for blasting and prep work.

Blasting and applying the epoxy should take a day, and you can begin flooring the next day without worry that your floor will ever have a moisture problem again. Smile
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#5
Yes, the source of the moisture was likely caused by a broken sprinkler pipe near the slab which caused the slab to become moist. My Wagner Rapid RH's are still showing 99%, and the slab has been open for months, with 2 giant dehumidifiers and 5 fans blowing for about 5 weeks.

People I talk to regarding french drains indicate that it is a bizarre thing to install in an old house that does not have standing water issues. Is this true?

Ultimately, I am trying to debate between Ditra, Koester, Ardex and Bonedry. They all sound great. I am worried that if I use Koester or Ardex, the very very high rh and vapor pressure will pop up the sealant or cause it to blister. If I use ditra, I am worried that my walls will become moist (but I heard this can be cured by ending the ditra before you hit the walls). Any advice?
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#6
It was great talking to you today!
I can alleviate your fears and promise you that Koster and Ardex epoxy mitigation systems WILL NOT pop off the floor. I have tested hundreds of installations with an Elcometer (pull tester) and the epoxy is much stronger than the concrete itself. Pulling the epoxy results in failure of the concrete it is bonded to, at a tensile strength of 300 psi to over 600 psi (depending on the strength of the concrete of course).
Another issue is the quality of the vapor retarder we are dealing with. Fixing a broken water line will remove much of the liquid water below the slab, but we always consider the ground to be at 100%RH. If the vapor retarder is damaged the slab will receive moisture from the soil forever. As long as the floor covering is more permeable than the slab there should be little problem, but a moisture sensitive floor may be problematic. And there could be a real issue with salts and alkalinity moving up through the slab, much like you see on brickwork where the vapor retarder is missing in a cool climate.
Regarding the drying time for a slab, your guess is as good as mine. I have had slabs poured at .50 and less water/cement ratio take many months to dry from 90%Rh to 75%Rh using professional dehumidifiers, and these slabs were raised and poured on steel pans so we know they were not absorbing ground moisture. If your concrete is rather porous it could hold a large amount of water in it that could conceivably take many many months to dry to 75% Rh, even years in your situation. And after the dehumidifiers are shut off the moisture may start climbing again.
I know you are trying to decide the right way to repair your problem, and I have a bias because that's what I do, but as you ask around I think you will find it really can be as easy as blasting and epoxying the floor with a top-shelf system. Wink

PS. Send me your email and I can send you some information....
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#7
I think you can install french drains outside the house as well especially if you have grading issues. Maybe they call them something else over there. Thats the first thing I look at when walking up to a house when I am going to give someone a bid. And it is usually the first thing a flooring inspector looks at. Been there done that.

But as far as wood and other moisture sensitive floorcoverings go the first step is to keep more water from getting to the slab!
Stephen Perrera dba
Top Floor Installation Co.
http://www.tucsonazflooring.com
http://www.floorsavior.com
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#8
Contact Ben Warner @ [email protected] Ben had a vapor transmission problem very similar to yours. He had installed an epoxy floor for a hospital, it failed 1 1/2 years later. He returned saw blisters, opened these and found water. He had installed this after confirming that the VT was 3lbs. The reading was now 8lbs and he could not understand this.

After calling all his contacts he was told to call me. I am not a flooring expert but a concrete hydration specialist. I asked him why he was surprised at the VT variation as OPC concrete is simply a hard sponge and any VT reading today can change tomorrow (as his did).

I am not going to tell you what I told Ben but if you call him tell him John Macdonald from Calgary told you to call him about water in your concrete and how to rectify this. After, if you believe Ben then call and I will explain to you how concrete without sealers, membranes or any other deflection technology can be it's own vapor barrier by simply managing the cement and water efficiently at the time of placement or reactvating the cement content 100 years later.

Best regards.
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#9
(11-01-2011, 11:19 PM)john macdonald Wrote:  Contact Ben Warner @ [email protected] Ben had a vapor transmission problem very similar to yours. He had installed an epoxy floor for a hospital, it failed 1 1/2 years later. He returned saw blisters, opened these and found water. He had installed this after confirming that the VT was 3lbs. The reading was now 8lbs and he could not understand this.

After calling all his contacts he was told to call me. I am not a flooring expert but a concrete hydration specialist. I asked him why he was surprised at the VT variation as OPC concrete is simply a hard sponge and any VT reading today can change tomorrow (as his did).

I am not going to tell you what I told Ben but if you call him tell him John Macdonald from Calgary told you to call him about water in your concrete and how to rectify this. After, if you believe Ben then call and I will explain to you how concrete without sealers, membranes or any other deflection technology can be it's own vapor barrier by simply managing the cement and water efficiently at the time of placement or reactvating the cement content 100 years later.

Best regards.

Hello John and welcome!

This 'reactivating the cement content' you speak of, is the reactive product fully accepted and will a full warranty be available from major glue manufacturers? Dodgy

JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#10
What happened is two things; You can't trust a cacl2 test and the slab had not gone into equalibrium.
It is true the water to cement ratio plays a huge part in the quality of ther concrete and how it dries. The ideal w/c ratio is 0.43 but the average in the US is 0.58. This is why some of the concrete takes so long to dry. At 0.60 it is no longer concrete it is crapcrete!
Rayt[/u]
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