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Q - What happens if I run
the calcium chloride test in less than 60 hours?
A - If the building has a highly
controlled interior atmosphere, the test can be run as short as 48 hours. However, the
purpose of running the test between 60 and 72 hours is to get a good sampling of the
moisture emission volume as a function of time. It is advised always, to conduct tests
according to industry norms.
VAPRECISION Professional
Vapor Emission Testing Systems
Q - What happens if I
run the calcium chloride test over 72 hours?
A - Depending upon the moisture emission volume, the test can stop
recording meaningful information when the dish of desiccant becomes totally saturated. If
the test runs over 72 hours (but not more than 84) and the crystals are not totally
liquefied, then the results are acceptable. However, it is best to take every precaution
that the 60 to 72 hour window is followed as it reflects the specifications set forth by
manufacturers regarding moisture sensitivity.
VAPRECISION Professional
Vapor Emission Testing Systems
Q - I forgot to
pre-weigh my crystals before exposing them!
A - The test will lose some of its value, but you can often use our own
quality control weights to get some evaluation of the moisture vapor emission. We maintain
between 30.0 and 30.5 grams in the tape-sealed container prior to exposure. If the test
results come out low, it is advised that you run them again to be sure. If the test
results come out very high (over 8 pounds for example) then the variability on the start
weight will not really influence the fact that the slab is not producing the 3 pound limit
most manufacturers specify anyway.
VAPRECISION Professional
Vapor Emission Testing Systems
Q - What are the options
to high moisture tests?
A - The problem of high slab emission is that long-term performance of
the floor covering is in jeopardy. The owner of the building must make a decision
regarding the floor covering. The history of the problem shows there are basically 5
choices:
1. Don't install a floor at all. The floor system will just fail.
2. Replace the concrete if old and permeable, or wait for it to dry
longer if it is a new slab.
3. Find an alternative floor system, if any.
4. Have the slab emission/alkalinity condition properly treated.
5. Risk the failure of the floor covering and install it anyway.
None of these decisions are easy to make, but the nature of moisture emission can be
incompatible with floor systems. Generally, calling in professional help has been far less
expensive than experiencing a floor failure.
VAPRECISION Professional
Vapor Emission Testing Systems
Q - Why can't tests be
conducted without proper climate control?
A - Moisture emission is contingent upon vapor pressure
differences between the substrate and room interior. Temperature and humidity together
creates a specific static vapor pressure. Concrete slabs often have a much higher static
vapor pressure than a room interior. Therefore, in order to accurately measure the
potential for a floor system failure, it is necessary to test for vapor emission in
respect to the operational-climate of the building.
VAPRECISION Professional
Vapor Emission Testing Systems
Q - What causes high
moisture vapor reading?
A - The concrete itself is a moisture-dependent mechanism. The
porosity of the slab, as a function of its design and placement, as well as the presence
and integrity of the vapor-retarder under the slab, all has an effect on topical moisture.
In addition, the surface profile (texture) and the building environment also play a role
in the moisture vapor emission.
VAPRECISION Professional
Vapor Emission Testing Systems
Q - What is the
relationship between Pounds & Percentage?
A - Pounds refers to the equivalent weight of water that has
escaped from 1,000 square feet of concrete area, in 24 hours. It is a measure of emission,
just like your breathing is a vapor emission. Percentage refers to the weight of the water
inside the slab, in relationship to the overall weight of the slab. Pounds is a
measurement of dynamic volume whereas Percentage is a measure of static content. So far,
there is no established relationship between the two measures. Many studies have been done
to find that correlation, but it isn't well defined. That is probably because other
variabls are at work, such as the porosity of the concrete, surface finish profile and
climatic variance between the slab and building atmosphere. Many European floor products
specify a certain Percentage of moisture acceptability. Nearly all American products
specify tolerance in Pounds. This is perhaps due to differences in construction technics
of concrete slabs. When confronted by these specifications, it is wise to use the Pounds
determination, as that is more relevant to American slab design.
VAPRECISION Professional
Vapor Emission Testing Systems
Q - Why the concern for
testing near cracks, joints and walls?
A - There has always been controversy about testing near cracks,
joints and wall perimeters as they can be obvious sources of elevated moisture emission.
Generally, we recommend that you collect test data away from these features, in
order to maintain a better sample of the overall slab emission. In some cases however,
like small closets or occupied homes, the perimeter is all you can have to work with. Keep
in mind that moisture levels near these features can be elevated, and not indicative of
the overall slab condition. Certainly the best information to be obtained is that from
both areas on the slab, where the contribution of cracks, joints and wall perimeters can
be better defined.
VAPRECISION Professional
Vapor Emission Testing Systems
Q - How do I work the
formula for calculation published by ASTM?
A - The American Society for Testing and Materials has recently
published the document F-1869 which must be purchased from ASTM and can be accessed by
clicking here. The formula for calculation of test results is as follows:
MVER = 24,000 X Gain / 453.612 X Area X Time
MVER = Moisture Vapor Emission Rate
Gain = Weight gain of calcium chloride crystals in
grams
*Area = Area of dome contact to slab, less area of dish
contact
in square feet.
Time = Exposure time in hours
*NOTE: There is some controversy as to whether or not the
dish in contact with the slab has any effect on moisture retardation, and therefore
whether or not it should be deducted from the area under the dome. Vaprecision had
traditionally NOT deducted this area in our calculations, however, in order to comply with
the newly published protocol, we will be adjusting the calculation. The net result
is a minor amount of variance in the overall test result.
The area of the Vaprecision dome is 70 square inches.
The area of the calcium chloride dish is 5.94 square inches.
The ASTM formulation calls for the Area, to be in square
feet. There is 144 square inches in 1 square foot.
Area (sqft) = ( 70 - 5.94 ) / 144 =
0.44486 square feet
Now, lets calculate results using a 3.0 gram gain over 72
hours:
MVER = 24,000 X Gain / 453.612
X Area X Time
MVER = 24,000 X 3.0 / 453.612 X
0.44486 X 72
MVER = 72,000
/
14,529.155
MVER =
4.95 pounds
Doing the same thing, this time without deducting the
area of the dish under the dome ( 70 / 144 = 0.486 ):
MVER = 24,000 X Gain / 453.612
X Area X Time
MVER = 24,000 X 3.0 / 453.612 X
0.486 X 72
MVER = 72,000
/
15,872.79
MVER =
4.54 pounds
As you see, there is a slight difference between calculations
of results when deducting the area of the dish under the dome.
The Vaprecision formula is essentially simplified, as we have
fixed sized dishes and domes. Traditionally, without deducting the area of the
dish, the calculation works as follows:
MVER = 108.846 X Gain / Hours
MVER = 108.846 X 3.0 / 72
MVER =
4.54 pounds
The NEW calculation Vaprecision will publish will comply with
the new ASTM protocol. For computation, we will carry out the decimal places as far
as they can go:
MVER = 24,000 X Gain / 453.612
X Area X
Time
MVER = 24,000 X Gain / 453.612 X
0.4448639 X Time
MVER = 24,000 X Gain /
201.7956
X Time
Taking the 24,000 and dividing by the 201.7956, we arrive at
a figure of 118.932 as the NEW constant. Using the same Gain and Time examples as before:
MVER = 118.932 X Gain / Time
MVER = 118.932 X 3.0 / 72
MVER =
4.95 pounds
This new constant calculates results per ASTM's formula,
except we simplify it to be a little bit more user-friendly!
VAPRECISION Professional
Vapor Emission Testing Systems
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