Thread: High moisture content reading in concrete slab

We recently started the process of replacing our flooring with new Laminate flooring. Upon removal of the old flooring which was Linoleum and carpet our flooring installer notified us that the moisture reading in our slab was to high to allow for Laminate, even with a moisture barrier installed. Since this time we have had all the testing done such as plumbing pressure leaks, sewage leaks, and soil core sample. The soil core test did show high moisture readings on the outside of our house, and the engineer attributed this to the A/C condensation pipe. This is operating within normal specs from my understanding although there is quite a bit of standing water. I have began the process of diverting the water away from my foundation. This does not yet seem to be making a difference. The odd thing is that there are only certain part of the slab that are showing high moisture content, and the readings are not consistant from one area of the floor to the other. In fact the highest reading is in our kitchen . There is somewhat of a pattern in that the reading are high in a straight line from our kitchen to our dining room and then perpendicular from the same point in the kitchen through to a hallway on the other side of the kitchen. I also noticed last night there seems to be consistant evidence of cracking in the areas of the high moisture reading. There is no visible water coming through, but the moisture meters used by the installer are showing the high reading. The type of meter they are using is the one with two prongs on the end and they simply touch it to the floor and get a reading and indicator light that shows red yellow or green. We are frustrated because other than the AC conensation theory no one has given any other thoughts as to the problem. any thoughts, advice or feedback would be greatly appreciated.

Similar Threads:

• High Efficiency Flue Termination
• MOISTURE DETECTION STICK
• SWITCH FROM HIGH HOME ENERGY BILLS TO PERMANENT ENERGY EFFICIENCY - World-Wire (press
• Concrete block

The moisture meter uses a high frequency radio wave to measure resistance in the material. They are generally designed to measure moisture content in wood, but only because water lowers the resistance of the signal.
Metal reinforcement, metal plumbing pipes, or metal ducts in the slab near the surface of the concrete will give a high reading.

Tape a piece of polyethylene to the floor. If the poly is dry underneath after a day or two, carry on with the new floor.

You don't give a time line as to the corrective efforts but once you get water under a slab it can take a long time for things to equal out. I don't have your specific answer but here are a few facts to consider:
all concrete cracks so unless it is a structural issue don't be caught up with a red herring issue trying to connect the dots,
There is moisture under all slabs everywhere,
Moisture can travel great distances in irregular patterns,
Your problem MAY be a lack of an intact vapor barrier under your concrete not an excess water problem, ground water sources rarely show up in convenient places.

That said, condensation dumping next to the foundation is never a good idea. Move it way from the foundation.
Have you done the plastic taped down over the entire floor area test?
This can give you an idea of where and how much moisture you are dealing with.

Your installer did you a favor! I have seen $30,000 worth of hardwood flooring curled and warped beyond use in less than a year due to lack of a vapor barrier.
My advice is to choose a flooring that is not moisture sensitive like ceramic tile and get on with life.

There are moisture meters that are designed specifically for concrete, so I would be careful not to disregard the warnings.

I find it hard to believe that a condensation line is putting enough water into the soil to get such a reading over such a widespread area.

What is the level of the water table? It may be ground water. I like the idea of the plastic test, but only to get a feeling as to what is going on. Get another opinion regarding the moisture content of the slab, or if you have confidence in what the installer told you, try to mitigate what he suggests the cause is.

The cost of the floor is too much to chance, especially when the contractor that is installing it tells you there is a problem. If you cannot mitigate the problem, choose a different flooring that is less sensitive to the moisture.

Thank you both for the feedback. I did do a plastic taped to the floor test(photos below) I did not do it on the whole floor but in the areas with the highest reading. the results showed moisture coming through within a few hours. I finally went ahead and removed the plastic after 18 hours I am also suspecting a possible issue with the moisture barrier in the foundation. Is there a way to check that? As far as choosing other types of flooring , I am sad to say that we were informed that the readings were so high that they could not even re-install vinal linoleum,wich is what we had previously. They may be able to install vinal plank with a high end moisture barier, but I am not ready to go that route just yet as I am concerned that the issue may cause problems down the road if we are not able to solve it before laying the new flooring. Would a foundation inspecter be able to do some testing that we may not have done to nail down the problem?

Steven, The soil core test seems to show normal moisture on one side of the house,but high moisture on the A/C side of the house. I do agree it seems unlikely the AC condenstion could be the source.I feel if that were the case the whole floor would show more consistant readings. As far as the meter being used, I would assume the installer(Home Depot) is using the correct type of meter for testing our slab. I have also thought of purchasing my own meter as well.

Originally Posted by Michael Wasson

Thank you both for the feedback. I did do a plastic taped to the floor test(photos below) I did not do it on the whole floor but in the areas with the highest reading. the results showed moisture coming through within a few hours. I finally went ahead and removed the plastic after 18 hours I am also suspecting a possible issue with the moisture barrier in the foundation. Is there a way to check that? As far as choosing other types of flooring , I am sad to say that we were informed that the readings were so high that they could not even re-install vinal linoleum,wich is what we had previously. They may be able to install vinal plank with a high end moisture barier, but I am not ready to go that route just yet as I am concerned that the issue may cause problems down the road if we are not able to solve it before laying the new flooring. Would a foundation inspecter be able to do some testing that we may not have done to nail down the problem?

Although it would be nice to know if there is a barrier or not, what good does it do you to know? Other than ruling out the lack of one, so you would look somewhere else.

If the water table is high, I would install a (somewhat deep) sump pump to lower the table. At the same time you could check for a moisture barrier. (even the you would only verify the one area (checked). You may find one where you look, but it may not be complete.

Originally Posted by Michael Wasson

Steven, The soil core test seems to show normal moisture on one side of the house,but high moisture on the A/C side of the house. I do agree it seems unlikely the AC condenstion could be the source.I feel if that were the case the whole floor would show more consistant readings. As far as the meter being used, I would assume the installer(Home Depot) is using the correct type of meter for testing our slab. I have also thought of purchasing my own meter as well.

As I stated, I find it hard to believe that a condensation line is putting so much water into the soil. I suggest you take a few steps back and look at the whole picture. Look at the grading on the side of the house, and anything else (including underground water).

Owning your own meter is nice, but will you ever use it again?

To offer an opinion, I would need to know:

• How old is the house?
• Describe the structure and relative elevations - I'm assuming slab-on-grade on block foundation, one or two courses exposed above exterior grade as typical.
• Specifically, what is the top of slab elevation compared to the exterior grade elevation?
• How long has the old flooring been off/concrete exposed?
• Is the house being air conditioned/what is the humidity level in the house and the temp of the concrete? (since pin type testing is being used, that is only measuring the surface moisture)
• The linear nature of the high readings - do they follow drain lines in/under the slab? The additional cracking you mentioned could be related to thinner slab thickness over the piping.
• Is there any efflorescence?

Two things to try:
1. Re-check with surface scanning meter vs. pin type (my meter has both options). In a development I was involved in, the flooring guy did an overnight, canister type test to determine concrete moisture; I don't remember more than that about it, but might be worth looking into (I wouldn't rely solely on pin-type surface testing). (Actually, come to think of it, my meter - Protimeter Surveymaster - has a probe attachment intended for small holes drilled in the concrete - that would serve).
2. Take your test patch and dry the hell out of it - fan, heater, blow dryer - whatever. Then re-cover and observe over a few days. Might help determine if it is surface condensation or through-slab moisture migration.

As previously stated, your installer is doing what professionals are supposed to do, not install a product in an area that is not suitable! He is a keeper. The meters that are designed to read moisture levels in concrete are not 100% dependable no matter what type or manufacture you use. They are merely an indicator and further testing (calcium Chloride testing) is needed to fully know what the levels actually are in the materials. Once you know the actual levels there are products that can be painted on the concrete to help mitigate some levels of moisture but most of your efforts have been to look for the cause and that is always best. If you want information on the products used to mitigate go to Armstrong’s website and type in concrete sealers into their search bar. Rebar and other unknowns can give false reading with induction and pin meters designed for concrete so the calcium chloride test is the "gold" standard.
Diverting condensate and any other potential water sources is a good idea no matter the outcome since these will improver the overall livability anyway.
If you cannot get a successful calcium test your best choice for flooring is ceramic or if you do not want ceramic then you can try one of the vinyl planks that interlock with adhesive.

Guys, there is no need for further testing, verifying levels, etc. It also makes no difference what the interior air humidity level is since the plastic test has indicated liquid moisture condensing from vapor coming through the slab FROM THE SOIL.
He has already tested everything with no plumbing or other leaks.
We KNOW the problem is excess moisture in the SOIL moving through the incomplete or missing vapor barrier.
Only three options exist: get rid of the water in the soil (almost impossible), put in a vapor barrier robust enough to handle the situation, or choose a less sensitive flooring product.
The cheapest and easiest is to choose a different flooring, carpet or masonry type tile that can breath and let the moisture move through, no harm or foul.

For those interested, air conditioning will be running at this area about 7 months out of the year unless the OP is a robust type, then only about 5 months! The area is hot and humid. And yes dumping 50 gallons of water a day in a concentrated location a few inches from the foundation is a stupid idea that WILL cause problems. (Remember the OP said standing water). Move the condensate line at least 5 feet from the house, preferably to a slope draining away from the foundation.

Originally Posted by Jim Luttrall

Guys, there is no need for further testing, verifying levels, etc. It also makes no difference what the interior air humidity level is since the plastic test has indicated liquid moisture condensing from vapor coming through the slab FROM THE SOIL.

I think it indicated the presence of moisture at the slab surface, but that test doesn't indicate the source.

Originally Posted by Jim Luttrall

For those interested, air conditioning will be running at this area about 7 months out of the year unless the OP is a robust type, then only about 5 months! The area is hot and humid.

Which is kinda what I figured. If the A/C has been off during the renovations, then the concrete, typically being the coldest surface, will sweat, a lot. I had a house like that (slab-on-grade, no A/C) and in high humidity conditions, the slab was wet, not just damp, far more than what I saw in the plastic-test picture.

Originally Posted by Jim Luttrall

And yes dumping 50 gallons of water a day in a concentrated location a few inches from the foundation is a stupid idea that WILL cause problems. (Remember the OP said standing water). Move the condensate line at least 5 feet from the house, preferably to a slope draining away from the foundation.

Which was why I asked about the relative elevations involved. While I understand that capillary action is not gravity driven, standing water at the same elevation is going to have a different impact than water 2 or 3 feet lower. Plus, you should find a 'spread pattern' coming from the source if it is the condensate puddle. Five minutes with my IR camera would settle that question.

I can't say that it isn't sub-slab moisture migration, I just haven't read enough to rule anything out. Especially with what I would consider to be inadequate testing (pin testing concrete? C'mon, man! At least drill a hole and probe test it a few inches down.)

Sounds similar to a situation I found many years ago in South Florida when I was doing home inspections there.

New house, I inspected it for the buyers as it was being constructed, and I got to see most of the work. The builder had to correct many, many, many flaws during construction, not the least of which was the tie-beam around the house had a required minimum size of 12" deep and many areas were only 9" deep. Their engineer ultimately decided the contractor needed to wrap the entire tie-beam in 1/4" steel plates 9" high, through bolted (all the way through the tie-beam) on 24" centers, staggered up and down the plate, 2" up from the bottom of the plate alternating with 2" down from the top of the plate.

Fast forward to completion of the house and a few months after my clients moves in:
- They called me and told me that their wood floor was wet in places, so wet that they could press on the wood with their thumb and water would seep out.

I went out there and, using my moisture meter, drew out the shapes of the moisture in the wood. The problem existed in several rooms so I did the same to all the rooms.

The shape of the traced out areas was wide in the center and tapering thinner out toward the long ends. I determined, as best I could, that there were no leaks - my clients had video recorded every step of the construction, including the underground plumbing before it was backfilled over. Without any outside cause from leaks, like in the case described here by the original poster, I determined that it had to be water from the soil, but what would cause/allow what I was finding?

I decided that when the slab was poured, the workers pouring the concrete would use a garden rake and lift the WWM from the bottom of the concrete (the WWM was in place and the concrete placed on top of the WWM) and pull the WWM up into the center of the concrete. I theorized that the rakes caught the edge of the plastic sheeting moisture barrier and pulled an area back, leaving a sort of rounded area with no plastic and the area tapering to nothing where the plastic had not been pulled back.

The contractor (builder) and I went round and round on this and they insisted that they were not going to address it because they knew I was wrong.

Finally they agreed to core out a 16" hole (the largest core drill they could readily get their hands on) and that if they were right and I was wrong then I would have to pay for all the testing and floor they had already pulled up. I agreed on the condition that when they found that I was correct that they would pay for all of the time that I had spent on finding what I found, and I guaranteed them that my cost would be greater than their cost.

The then agreed to do it at their cost.

What we found was no plastic sheeting in that 16" core drilled hole. We could feel the plastic about 2" back from each edge with our fingers under the slab.

THEY now had a major problem on their hands. They eventually bought the house back from my client and made my client whole (including all of the decorators costs spent on the house - everything).

I.e., *IT COULD BE* missing or pulled back plastic sheeting.

..........Once you correct the water issue from the condensate drain, you might just be able to help dry things out with the installation of a radon mitigation system. Along with radon removal, they typically remove lots of water vapor..............Greg.

Originally Posted by Mark Fisher

I think it indicated the presence of moisture at the slab surface, but that test doesn't indicate the source.

That is what the plastic test does best. Dry to the touch concrete becomes wet when covered with plastic. The moisture is coming from the slab or more specifically, the soil under the slab.


Which is kinda what I figured. If the A/C has been off during the renovations, then the concrete, typically being the coldest surface, will sweat, a lot. I had a house like that (slab-on-grade, no A/C) and in high humidity conditions, the slab was wet, not just damp, far more than what I saw in the plastic-test picture.

If the slab was wet before testing with plastic it would support this theory but that is not what the OP indicated. Couple that with a presumed longer period of time rules out condensation from the air.

Which was why I asked about the relative elevations involved. While I understand that capillary action is not gravity driven, standing water at the same elevation is going to have a different impact than water 2 or 3 feet lower. Plus, you should find a 'spread pattern' coming from the source if it is the condensate puddle. Five minutes with my IR camera would settle that question.

Water migrating through a slab in vapor form will not necessarily present a pattern of the water "puddle" or source but rather the area with the most vapor permeability. I can't comment on the IR question but I assume it will only tell you the relative temperature and by inference the "wetness" of the slab, not the source.

I can't say that it isn't sub-slab moisture migration, I just haven't read enough to rule anything out. Especially with what I would consider to be inadequate testing (pin testing concrete? C'mon, man! At least drill a hole and probe test it a few inches down.)

If we already know the slab is wet and the water source is the slab what will drilling deeper holes for the probe pins do for you?

Originally Posted by Jim Luttrall

If we already know the slab is wet and the water source is the slab what will drilling deeper holes for the probe pins do for you?

Give a warm and fuzzy feeling?

The plastic covering test answered the question of moisture coming through the slab.

Unless one REALLY wants to get into finding out the cause and then curing it, a better option may be to just deal with it with the best moisture barrier one can get. I've had engineers tell me that when they have had a problem like that in a residence, what they did was lay down two layers of vinyl flooring, with the second layer perpendicular to to the first layer, and that if you will be laying down 6 foot wide sheets, mark out where the seams will cross and place an additional piece of plastic sheeting below the first layer and between the two layers at those points. With two layers perpendicular to each other, there will be one pin-hole opening at each 6 foot by 6 foot grid point where they lap, not much moisture to worry about at those few pin-point locations, then the additional plastic sheeting at those locations should take care of those openings.

You will want to leave the vinyl slightly short of the edges at the walls and remove the baseboard. After the wood flooring is installed with a gap around the wood to the walls for expansion, install new base up off the wood flooring slightly, that will allow any moisture which tries to get through the vinyl to migrate to the edges and then up and out into the room where the air conditioning can take the moisture out through dehumidification.

I really appreciate all the feedback and advice I am getting. The frustrating part of this is that the readings are so random. My installer has told me that they can likely do the vinal plank with the snap lock edges. This product actually has no moisture spec requirement. He also said they would put down the 6 mil poly barrier (which ever one is the best). I am waiting first to here back from the warranty company for my home. My builder is DR Horton and they cover the home for the first 3 years then the warranty is covered by Residential Warranty Company for years 4-10. We have been in the home and are the original owners. We are on year 8 and there is a 10 year warranty on the home. DR Horton however is not being very cooperative in assisting me. They did cover the core sample testing but even at that they are not wanting to acknowledge the engineers recommendation. Here is what the test results said: Borings were taken at each corner of the house on the left side (when viewed from the street. Additional boring were taken by the AC unit and at the right rear corner of the home. Water was observed standing on the ground near AC unit covering approximately 20 SF of ground with proximately 1" of water. CONCLUSIONS AND RECOMMENDATION: Soil depth under home varies from 3-6 feet. Boring 3&4 on left side of the home had normal moisture content of proximately 20%. Moisture content at right rear corner of home was 30%(very high) Moisture content at AC unite was 40% (extremely high). We believe source of moisture in ground and under home is coming from the ac unit. We recommend ac unit drain pipe be placed in a buried drain pipe and day lighted approximately 10 from from front house towards street. My next question would be this: would it be worth it for me to actually have an inspector who specializes in foundations come out and look it over. All I get from my floor installer and most regular people I talk to is a blank stare and amazement at my situation because they have never heard of or seen a scenario such as this.

A subfloor consisting of OSB on plastic nubs could be laid down. These are square tiles specifically designed for damp concrete flooring. Conventional wood flooring or laminate can be laid on the subfloor. The raised plastic nubs allow a bit of air flow under the wood.
You will have to trim the doors and door trim to clear the raised floor.

Number one, stop that water from flowing under the slab.

I have only heard of this process, and I'm sure it is costly. In a wet basement floor which is not as thick as a slab, holes were drilled in the concrete about 2 ft apart and a poly material was injected under the concrete, flowing together to form a tight vapor barrier.

Follow the soil engineers recommendations!
Move the condensate drain!!
Dump it into the city sewer unless there is a prohibition against this practice (not likely.) The standard practice in the DFW area is to dump all condensate into the city sewer due to the expansive clay soils in the area.
This is a cheap and effective solution almost guaranteed to at least lessen the amount of water. This is not a total solution but will greatly reduce the measures needed to deal with the rest of the story.
Be aware that this will take time to see the results. You have had 8 years to build up the water under the slab and it will take a minimum of at least that many months to see the moisture content stabilize at a lower level.
Also your engineer report said there was "standing" water approximately 1 inch deep. Correct the soil slope so there are no areas of flat or negative slopes around the house. There should be enough slope to drain all water away from the house. 6" in 10' fall is the standard.
After hearing the engineers findings I would be much more confident about putting down a robust vapor barrier (after addressing the cause) under the new floor and getting on with life.
Cheap, easy, no stress.

Originally Posted by Michael Wasson

I really appreciate all the feedback and advice I am getting. The frustrating part of this is that the readings are so random. My installer has told me that they can likely do the vinal plank with the snap lock edges. This product actually has no moisture spec requirement. He also said they would put down the 6 mil poly barrier (which ever one is the best). I am waiting first to here back from the warranty company for my home. My builder is DR Horton and they cover the home for the first 3 years then the warranty is covered by Residential Warranty Company for years 4-10. We have been in the home and are the original owners. We are on year 8 and there is a 10 year warranty on the home. DR Horton however is not being very cooperative in assisting me. They did cover the core sample testing but even at that they are not wanting to acknowledge the engineers recommendation. Here is what the test results said: Borings were taken at each corner of the house on the left side (when viewed from the street. Additional boring were taken by the AC unit and at the right rear corner of the home. Water was observed standing on the ground near AC unit covering approximately 20 SF of ground with proximately 1" of water. CONCLUSIONS AND RECOMMENDATION: Soil depth under home varies from 3-6 feet. Boring 3&4 on left side of the home had normal moisture content of proximately 20%. Moisture content at right rear corner of home was 30%(very high) Moisture content at AC unite was 40% (extremely high). We believe source of moisture in ground and under home is coming from the ac unit. We recommend ac unit drain pipe be placed in a buried drain pipe and day lighted approximately 10 from from front house towards street. My next question would be this: would it be worth it for me to actually have an inspector who specializes in foundations come out and look it over. All I get from my floor installer and most regular people I talk to is a blank stare and amazement at my situation because they have never heard of or seen a scenario such as this.

Michael,

An interesting read on this post with a lot of good information. As noted above it was a good thing the floor installer was actually taking moisture readings. That is a huge plus.

If you are interested in yet another view (objective, very good and is a licensed Professional Engineer well versed in such situations) please send me an off-line e-mail and I'll provide his contact v-card.

He happens to live/work in Round Rock as well.

You can reach me at: Nolan@NolansInspections.com

BTW - the comments from the builder are not unusual.

Quote:
Originally Posted by Mark Fisher
I think it indicated the presence of moisture at the slab surface, but that test doesn't indicate the source.

That is what the plastic test does best. Dry to the touch concrete becomes wet when covered with plastic. The moisture is coming from the slab or more specifically, the soil under the slab.

He didn't say if or how he dried the surface of the test patch. I'm not saying you're wrong, but it is a big step from confirming the presence of moisture to confirming its source.

Which is kinda what I figured. If the A/C has been off during the renovations, then the concrete, typically being the coldest surface, will sweat, a lot. I had a house like that (slab-on-grade, no A/C) and in high humidity conditions, the slab was wet, not just damp, far more than what I saw in the plastic-test picture.

If the slab was wet before testing with plastic it would support this theory but that is not what the OP indicated. Couple that with a presumed longer period of time rules out condensation from the air.

I thought the slab was wet, or why else are they doing all this? And a presumed longer period of time of what? I didn't know if this house is 6 months or 60 years old, or if they stripped the floor 6 days or 6 months ago. That's why I was asking.

Which was why I asked about the relative elevations involved. While I understand that capillary action is not gravity driven, standing water at the same elevation is going to have a different impact than water 2 or 3 feet lower. Plus, you should find a 'spread pattern' coming from the source if it is the condensate puddle. Five minutes with my IR camera would settle that question.

Water migrating through a slab in vapor form will not necessarily present a pattern of the water "puddle" or source but rather the area with the most vapor permeability. I can't comment on the IR question but I assume it will only tell you the relative temperature and by inference the "wetness" of the slab, not the source.

I disagree. The water IN the slab (or other solid) is not vapor form. It moves via capillary action in liquid form on the molecular level from a wetter area to a dryer area until equilibrium is achieved. If there is a single point source of all of the moisture, you will see a higher saturation level at the source and a lower level the farther away from the source you get, until equal saturation is achieved - actual moisture content a factor of soil type and density. The InfraRed signature of a solid changes significantly when wet, and the pattern going from saturated solid to less saturated solid is dramatically evident. It doesn't actually measure temperature, it detects electromagnetic radiation in the infrared range (versus visible light or radio waves, etc.) and that changes a lot when a solid gets wet.

I can't say that it isn't sub-slab moisture migration, I just haven't read enough to rule anything out. Especially with what I would consider to be inadequate testing (pin testing concrete? C'mon, man! At least drill a hole and probe test it a few inches down.)
_______________

Originally Posted by Jim Luttrall

If we already know the slab is wet and the water source is the slab what will drilling deeper holes for the probe pins do for you?

Pin testing only measures what is in between the pins. It works on wood because it can penetrate 1/4-1/2" so you are testing a 'chunk' of the wood. Simply touching the pins to the concrete (no penetration) is only measuring the surface, which is affected by atmospheric conditions, mostly humidity. Drilling even an inch, and using the correct probes, means you are actually measuring the concrete, which is what this is all about.

The OP has said that the slab moisture readings are "random". He has also reported that the exterior soil moisture levels show no elevated moisture on one side of the house, some elevated moisture at one corner, and (obviously) high moisture at a known point source. So, how does the slab get saturated from the soil, when the adjacent soil isn't saturated?

Look, we have a known point source. Correct it, certainly, but automatically attributing all of your problems to the first, most obvious cause is something we see contractors do. We are supposed to be smarter, or at least more thorough.

Again, I recommend doing an infrared scan. Simple. Clean. Fast. I would, if this was my client, supplement with a few properly performed meter tests to establish moisture levels (IR shows relative saturation, not %) and confirm. If the results match the soil results (higher saturation nearest the 40% soil going to lower saturation nearest the 20%), that would confirm the point source (A/C condensate) as the cause. If not, then other factors are in play.