Epoxy & fiberglass flooring, seamless fiberglass wall systems, sealers, high performance coating systems, and industrial cleaners

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918 N. Union Street













Appleton, WI 54911












920
-
739
-
8685











or 1
-
800
-
221
-
6381













Fax: 920
-
739
-
8704

EMAIL: CDPEPOXY@AOL.COM


Epo
xy & fiberglass flooring, seamless fiberglass wall systems, sealers, high performance coating
systems, and industrial cleaners


WATER VAPOR EMISSIONS THROUGH CONCRETE



Water vapor emissions (WVE) through concrete are impossible to stop, difficult to a
nticipate, frequently
misunderstood, and heretofore unquantifiable and uncorrectable. Recent advances in the understanding of

the circumstances surrounding this problem have led to a deeper understanding of the causes, quantitative tests to describe
the p
roblem, and products to minimize it.


Water vapor emissions are often thought of and tested for as if there is actual water pressure (a static head of water)
pushing water through the concrete. The use of a sand filler under the concrete is considered

as the defense against water
vapor, since sand will drain (liquid) water well. This thinking is inadequate since water vapor is a gas (measured as
relative humidity) which easily passes through any sand layer. Concrete is a complex mixture of water, cem
ent, sand and
rock which is hydrophilic (likes water), readily absorbs and is permeable to water vapor. Concrete will continually
absorb and emit water vapor. The rate of the WVE, and its control, are what is important.


There is a test for vapor em
issions, which we (or you) can perform to determine the water vapor emission rate through
concrete. This test utilizes a desiccant chemical placed on your concrete floor under a small air/watertight plastic dome.
After a 60
-
72 hour exposure at between 6
0F and 85F, the sample is weighed and the difference of the before and after
weight (the water absorbed) is used to calculate the water vapor rate emission. Based on this rate, your flooring may or
may not be secure. Roughly a rate below 3 lb. water vapo
r emissions per 24 hrs per 1000
-
sqft surface area is acceptable
for all flooring. Rates between 3
-
6 are very questionable and rates over 6 are generally a cause for problems. A recently
tested area in a supermarket showed a rate of 7.2. This facility had

a long history of VA tiles coming off, and an epoxy
floor bubbling off, each within a few months of installation.


The reasons why a section of concrete may have a high vapor transmission rate will vary (often being effected by
several things at once)
. The following correlations seem valid.


1. As concrete density goes up WVE decreases.


2. As concrete compression strength increases WVE decreases.


3. WVE increases directly, and considerably, with the use of chloride accelerators.


4.
Air conditioning systems, which maintain a low relative humidity, will draw moisture through the concrete


in direct proportion to the difference in the relative humidity below( nearly always 100%) and above the slab.


5. Temperature difference
s across the slab will draw moisture through in direct proportion to that


temperature difference.


6. As the water/cement ratio in the initial concrete pour goes up so does the porosity of the concrete and hence the


WVE



If the te
sted water vapor transmission rate is too high for flooring to adhere, please contact us for recommendations,
otherwise wait and test again. We generally estimate 1 point drop per week in a well ventilated, fairly dry, construction
environment. The use of
additional heat and/or ventilation is helpful. Desiccant dryers are also useful. Reductions of
roughly 40% per coat can be attained by the application of NUPRIME, with the advantage that most subsequent coatings
may be applied soon after the NUPRIME has
cured. We will provide the moisture test units, provide and/or describe the
necessary surface preparation, and supply the NUPRIME epoxy primer. Our other epoxy and urethane toppings and
coatings have been tested and are compatible with the each product s
ystem and certainly we will supply any materials or
installations as needed.


If we can be of further assistance please feel free to call. Thank you for your time and consideration.

TOM HENNESSY FEB, 1992




www.Concretedefense.com

ADDITIONAL:


Refer to the moisture vapor cu
rve chart. This chart is most useful in both explaining moisture vapor transmission
characteristics of concrete, predicting the drying of the concrete and discussing ahead of time with customers and
contractors the desired concrete blends for optimal dryi
ng of the concrete.


On the horizontal is days and on the vertical is the moisture vapor level expressed in lb of moisture vapor per 24
hours per 1000 sqft of concrete. This has become a typical and wide spread unit commonly understood in the flooring
trad
es. Generally rates from 4 and below are fine for any type of flooring application, 4
-
7 or so are marginal, 7
-
10 are
most likely to cause troubles
-

delamination bubbles etc
-

and over 10 are most certainly going to be trouble. The curves
represent differe
nt water/cement so when the ratio is low eg 0.4 or so the concrete dries faster and when it is high it takes
way longer to get to a low enough reading for flooring to be installed.


For any water/cement drying is speed up with higher temperatures in the ar
ea, lower relative humidity, more air
flow, and not applying a cure and seal. The common 28 day rule of thumb is shown to be applicable for 0.4 water/cement
at 50% RH at 70F for a 4” slab in a well ventilated area. As you can see this level of 0.4 might
take a considerable time to
get to if the cement is poured wet, the temperature is low, the RH is high or a cure and seal is applied.


If the MVT is high either wait until it is low or increase drying with a dryer/dehumidifier. If you go ahead when
the MVT

is too high you are running a risk of failure which can be very expensive.


We report the MVT on the MVT report form also included for your review.

Tom Hennessy Sept 2004.