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Moisture at Floor - Slab on Grade


desertdweller
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Hello All- Hoping you can help

Just inspected a 3 yr old home in the phoenix area. The home is slab on grade. The seller disclosed previous issue with excessive moisture build up b/w carpetpad and foundation. Builder documented (at 1.5 yrs old) the issue as ordinary residual moisture from the concrete that collected beneath one of those plastic office chair mats.

I tested multiple areas throughout the home (primarily tiled areas) with GE Protimeter Surveymaster) The reading was off the chart (in the 700's range in relative moisture) in 8 of 10 locations. I tested beneath carpet and had same experience.

Checked for slab leak - none. Decent drainage with little recent rain.

What do you think would be the cause? What are potential issues?

Would carrying on with decent ventilation within the home be sufficient?

The buyer asked about putting in Pergo - I said not a good idea as it would trap the moisture.

Please share your thoughts.

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Is this irrigated property? If not, are there bubblers or sprinkler heads by the house? Does this house have copper pipes? I would guess a pinhole leak in the copper pipes or a broken sewer pipe. Yes, this would be a major concern especially if in an area with expansive soil.

Jeff Euriech

Peoria, Arizona

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The source of the moisture may not be external. Interior moisture could be condensing on the surface of the cool slab.

Another thought...I own the Surveymaster as well and its performance over concrete and tile is abysmal. Moisture in the ranges you're talking about having measured should have been plainly visible on concrete.

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No irrigation. 3 Year old tract with PEX through the ceiling. No indication of leak at supply to main. Yes expansive soils are an issue.

Any thoughts on type of specialist to refer them to??

Originally posted by JEuriech

Is this irrigated property? If not, are there bubblers or sprinkler heads by the house? Does this house have copper pipes? I would guess a pinhole leak in the copper pipes or a broken sewer pipe. Yes, this would be a major concern especially if in an area with expansive soil.

Jeff Euriech

Peoria, Arizona

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I considered the unreliability of the surveymaster. That may be the case yet I dont think so. I tested on the tile as well as pulled corners of carpet to test on slab with similar findings. Tried it inside and out (outside had much lower readings) the home is vacant so it probably is not aired out allowing the moisture level to build up.

Originally posted by Chad Fabry

The source of the moisture may not be external. Interior moisture could be condensing on the surface of the cool slab.

Another thought...I own the Surveymaster as well and its performance over concrete and tile is abysmal. Moisture in the ranges you're talking about having measured should have been plainly visible on concrete.

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The buyer asked about putting in Pergo - I said not a good idea as it would trap the moisture.
This is from the Pergo.com website (my bold).

9. CONCRETE AND TERRAZZO SUBFLOOR REQUIREMENTS

When installing Pergo flooring, the maximum acceptable moisture reading for concrete subfloors is 4.5% or a moisture vapor emission rate of 5lbs/1000sq. ft./24 hrs.

a. Concrete and terrazzo release moisture long after it is poured and can transfer dampness from wet soil and the air, i.e., elevated concrete floors in apartment and office buildings. New concrete must cure for 60

days before any flooring is installed.

b. Check the floor for flatness. If the concrete or terrazzo subfloor has excessive voids or variations, a leveling compound can be used to bring it up to specifications. (See Subfloor Requirements/General.) Low areas greater than 3#8260;16" in a 10' radius should be filled in using a Portland cement and latex-based floor leveler. Follow the manufacturer’s directions for mixing the filler, and be sure to allow it to dry completely. High spots or ridges above 3#8260;16" within a 10' radius must be ground down.

c. When installing Pergo flooring over a concrete or terrazzo subfloor you must use a 6-mil. (.15mm) nonrecycled (100% virgin) resin polyethylene film such as Pergo MoisturblocTM or Pergo SoftSealTM combination foam/film to form a vapor barrier. When the Pergo Product has an attached underlayment foam, use only a vapor barrier with this product when installing over a concrete subfloor. The edges of the vapor barrier must overlap by at least 8 inches (200mm) or when using an equivalent, non-recycled, polyethylene film, follow the manufacturer’s direction for installation. Vapor barrier underlayments are required over all subfloors containing concrete, even if the concrete is covered by vinyl, linoleum VCT (resilient tile), terrazzo or ceramic tile.

d. Evaluation of moisture conditions for concrete or terrazzo subfloors. (Also see Job Site Evaluation–exterior and interior moisture conditions–section 6.) If there is excessive moisture in the concrete or the job site

conditions are not correct then Pergo flooring cannot be installed.

e. When a resilient tile is installed over concrete subfloors and there is visible salt deposits at any of the joints of the tile there is reason to believe that excessive moisture is present.

f. A precise moisture reading can be obtained using the Calcium Chloride Test. Three tests must be used for the first 1000 sq. ft. and one additional test for each 1000 sq. ft. or fraction thereof (ASTM 1869-03). The results of the tests must not exceed 5lbs/1000 sq.ft/24 hrs (not to exceed five pounds of water vapor being emitted from 1000 square feet of flooring over a period of 24 hours).

g. Moisture meters, correctly calibrated, and used can also provide moisture readings. See the meter manufacturer’s instructions for use and interpretation of the meter readings.

h. Do not install Pergo flooring in a room with a floor drain.

i. Do not install Pergo flooring over a floor with a sump pump. Pergo flooring must not be installed over any floor that has a sump pump, i.e. should there be a floor at a below grade or an on-grade level concrete slab in the home and a sump pump is located in that below-grade level flooring or in the on-grade level slab, then Pergo flooring cannot be installed anywhere on that floor.

IMPORTANT NOTE: During a dry season, you may find that you get an acceptable moisture reading even if other job site conditions are not acceptable. Before installing Pergo floors, you must be sure that your job site conditions as well as your moisture readings are acceptable.

j. Should excessive moisture be present or the job site conditions are not correct, consult a waterproofing or flooring contractor for further moisture testing or abatement before installing a Pergo floor.

I think I'm with Chad. I'm not sure that the near-surface 700 surveymaster readings on a slab just after the pad has been pulled up are really that indicative of a problem. You would expect much lower readings on exposed concrete outside. It would be interesting, but for us impractical, to take readings after the carpet/pad had been pulled up for a few weeks with some ventilation.

I guess my point is that I wouldn't be comfortable saying that Pergo could or could not be used and would probably recommend the "waterproofing or flooring contractor for further moisture testing or abatement". I would assume one of those guys would have a better testing method than is available to us during a quick inspection (unless you want to spring for a dedicated deep reading concrete meter).

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I am not at liberty to discuss this property in detail at this time. I may have to testify in the case as I performed some of the testing.

I just wanted to warn a fellow inspector of potential issues.

Now I have a different question.

Who is John Reems? I clicked on Desert Dwellers profile and the name is John Reems. But I can't find this name in any org listing or on the States listings of professional home inspectors.

John I am not saying that your not state certified, I just couldn't find your listing.

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I can tell you that there is a house close to Avondale (where Desert Dweller says he is from).[:-dev3]

The house is one year old. Never been lived in. [:-boring]

Protometer reads from 50%-99% depending on where you take readings.

Slab on grade, 4, 8" cores were drilled through the floor. Slab is at least 6" thick. Moisture present under the slab.

Calcium chloride tests were performed twice. The first time someone tampered with the tests. The second time, the person who did the testing was ordered by his client not to release the results.

Water line and sewer line have been tested with no leaks. However owner complains of funny taste in water. I believe it is a copper service with PEX on the interior of the home.

Landscaping is only in front yard and is a drip system for desert plants.

No irrigation in the area. Housing development is about 80% complete.

No swimming pool at this home or at any of the next door neighbors.

House sits on a corner of a small residential street. Storm drainage is away from the home.

Grade is away from the home.

If this is the house your talking about, Be very careful.

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