Thread: moisture meter test substrate

Hi everybody

I always think why we can use moisture meter to test the shower wall substrate but not the 10th concrete floor around toilet on highrise. I know we can not test the basement & slab on concrete floor. in the concrete never dry? So, is it very different from motar which glue the tile at shower?

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The floors in a condo building are always reinforced with steel. I'm pretty sure that is why we get high readings on moisture meters. The meter measures resistance or something similar by passing a radio wave through the material. The meters we use are calibrated to measure moisture in wood, so do not give accurate moisture readings in other materials. We use them anyway, because if there is an abrupt change in the reading, that may be due to moisture. It can also mean you've found some metal or some other material.

Thank you John. But the meter is only testing up to 3/4" depth

This came up a while ago when I had an inspection in an exposed concrete NC condo building. I have a Delmhorst meter that has a concrete setting. Not sure how much more accurate that makes it for basic measuring.
The following info was posted by another member. I think Jerry or Raymond posted it. Hope it clarifies the question a bit for you.
Concrete lift buckets used with cranes, ¾ & 1 ½ yards standard size

Here are a few points on concrete moisture:

Moisture meters are not suitable to make the final determination as to whether or not concrete is dry.
No moisture meter of any type can give consistently accurate moisture readings across the different mixes and densities of concrete. Other components such as metal reinforcing steel, aggregate size and amount can cause false indications of moisture, especially with non-pin meters. Pin-type moisture meters are also not practical for moisture measurement due to the variable chemical and physical characteristics in concrete can cause false readings due to the electrical resistance that have nothing to do with moisture.


Keep in mind, that whether a floor or wall, relative humidity gradient throughout its thickness is greater at the 40% to 50% depth.

The RH will be much higher at those levels in depth. The surface of the concrete will more likely reflect the RH in the room or building which gives no indication of the potential for a dry concrete.

Here is an article that some might be interested in:

Concrete moisture vapor emission is a natural constituent of any concrete slab. It may be encountered as the emission of mix water during the drying process of a new concrete slab. Concrete drying creates an emission from the slab regardless of whether the concrete slab is below, on or above grade. Moisture vapor emission from suspended concrete is often overlooked as a potential cause of floor covering failure and this specific problem may be exacerbated by the use of light-weight aggregates . Beyond the drying process, moisture vapor emission may be the result of moisture vapor transmission from sources below the slab. The moisture source can be water trapped in a blotter course over a vapor retarder or moisture from the earth passing through the slab system. The major concerns surrounding this issue have been driven by changes in floor covering adhesives and coatings, which are more sensitive to moisture and alkali attack than previous materials. More important than floor covering system failure is the concept that Sick Building Syndrome and other I.A.Q. issues often start at the floor surface and are fed by the high sustained humidity levels created by excessive concrete moisture vapor emission.

The Calcium Chloride Vapor Emission Test has been developed to quantify, in a meaningful way, the amount of moisture vapor emitting from the surface of a concrete slab. It has been known as the R.M.A. Test, the Moisture Dome Test and by it's current name. ASTM has published a standard for the use of calcium chloride to measure moisture vapor emission from concrete, ASTM F1869-04 is the most current edition of the protocol. The results, reported as "pounds per one thousand square feet per twenty-four hours" are accepted by most flooring, adhesive and resinous coating manufacturers in establishing the benchmark of acceptability for the installation of their products over a concrete substrate. The test is performed by placing a quantity of calcium chloride in an open dish and placing the dish on a clean concrete surface. The dish is covered by a dome of approximately 9" x 9" and 2" in height. This dome is sealed to the concrete to prevent normal humidity in the room from affecting the test. The test apparatus is left undisturbed for a period of from 60 to 72 hours. At the end of the test period the dish is retrieved and any weight gain experienced by the dish is attributed to moisture leaving the concrete and being absorbed by the calcium chloride. Through calculation, the test results are extrapolated to approximate the equivalent number of " pounds" of emission as outlined above. It should be noted that the environment of the air space in the building envelope is of critical importance during the test series. As discussed earlier, the vapor pressure differential, created by temperature and humidity have a controlling influence on moisture vapor movement. Testing should take place in a building envelope conditioned to the same ambient temperature and relative humidity levels as the occupant/tenant will require during use of the space. If these conditions cannot be met, the ASTM standard offers tolerances which, at a minimum, should be honored if accurate test results are anticipated. Testing in a non-acclimated environment leads to erroneous results. Per ASTM, test density is required to equal 3 tests in the first 1,000 square feet, with one additional test per each additional 1,000 square feet of concrete slab surface.

Originally Posted by Peter Louis

Hi everybody

I always think why we can use moisture meter to test the shower wall substrate but not the 10th concrete floor around toilet on highrise. I know we can not test the basement & slab on concrete floor. in the concrete never dry? So, is it very different from motar which glue the tile at shower?

It depends on the type of moisture meter you are using. For tile, the Protimeter SM is your best bet. It uses radio frequency over electrical resistance.

With a shower it helps a great deal to also know what type of shower pan you are dealing with.

Around toilets the SM also works well. You can see the relative moisture in the concrete/flooring change as you move it around. If it shows higher as you move closer to the toilet then you also have an increase in moisture which would 90+% of the time correlate with a leak.

Originally Posted by Scott Patterson

If it shows higher as you move closer to the toilet then you also have an increase in moisture which would 90+% of the time correlate with a leak.

This is always I am thinking about. Basically we only need the relative readings to show the Mositure content change. But what happened is there is a metal reinforcing bar there?

[quote=Scott Patterson;145075]
With a shower it helps a great deal to also know what type of shower pan you are dealing with.

quote]

How can we tell this?

[QUOTE=Peter Louis;145095]

Originally Posted by Scott Patterson

With a shower it helps a great deal to also know what type of shower pan you are dealing with.

quote]

How can we tell this?

Most of the time you can't.

Originally Posted by Peter Louis

This is always I am thinking about. Basically we only need the relative readings to show the Mositure content change. But what happened is there is a metal reinforcing bar there?

The metal re-bar will most likely peg the meter. This is where experience is the best teacher and it is something you just have to experience in the field.

Originally Posted by Scott Patterson

The metal re-bar will most likely peg the meter.

Steel reinforcement, when picked up, can be traced out the length of the steel until it goes deeper and maybe even fades out. That could also be a post tension tendon.

If the relative reading goes higher is a large area, that is likely increased moisture level, of it could be a slab penetration which was not properly firestopped and moisture from below is transmitting through the concrete slab at it few available openings.

so helpful, Thanks guys.

When I read the paint & stain, one article said Oak & birch are not supposed to stain. Is it because they are hardwood & not really porferated porous?

Originally Posted by Peter Louis

so helpful, Thanks guys.

When I read the paint & stain, one article said Oak & birch are not supposed to stain. Is it because they are hardwood & not really porferated porous?

You mean water stains? Don't believe it. Water will leave a black stain in oak or birch.
It is difficult to apply a colour stain to some hardwoods, if that's what you mean, yes, because it will not penetrate into the wood fibre as well. But there are dozens of different types of oak. I think oak grows in every country in the world. We have an oak dining room set, Malaysian oak, that is stained. Where do you get this info?

It comes from internet. When I googled Paint vs stain.