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Flooring Over Concrete Slabs:
Avoiding Failure Through Moisture
Mitigation and Proper Design
Sealflex Industries, Inc.
2925 College Avenue, Suite B4
Costa Mesa, CA 92626
Tel: 714.708.0850
Fax: 714.708.2711
Toll-Free: 1.800.651.2098
Web: www.sealflex.com
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© 2004 Sealflex Industries, Inc. The material contained in this course was researched, assembled, and
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Slide 1 of 56
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Flooring Over Concrete Slabs
Flooring Over Concrete Slabs
Presented By:
Sealflex Industries, Inc.
2925 College Avenue, Suite B4
Costa Mesa, CA 92626
Description:
Provides an overview of the role of moisture and alkalinity
in flooring system failures and options for mitigating
moisture migration through concrete slabs.
AIA/CES Info:
Provider No. J624 – Course No. AEC018; LUs – 1.00
MCE Info:
Contact your respective governmental licensing & regulatory
agency. This program qualifies for HSW credit.
Expiration date:
June 30, 2005.
This program is registered with AIA/CES for continuing professional registration. As such, it does not include content that may be deemed
or construed to be an approval or endorsement by the AIA or AEC Daily Corporation of any material or construction or any method or
manner of handling, using, distributing or dealing in any material or product. Questions related to specific materials, methods and
services should be directed to the program instructor.
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Flooring Over Concrete Slabs
How to use this Online Learning Course
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Flooring Over Concrete Slabs
Learning Objectives
Upon completing this course, you will have a better understanding of:
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The nature and composition of concrete and why moisture is a problem
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The potential for flooring system failures installed over concrete slabs
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The importance of controlling moisture migration and alkalinity of concrete
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How to test for and recognize potential moisture and pH problems
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How to design and specify moisture protection for floors installed over concrete
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How to mitigate moisture migration using in-situ repair systems
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Slide 4 of 56
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Flooring Over Concrete Slabs
Moisture & Concrete Basics
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Flooring Over Concrete Slabs
Moisture & Concrete Basics
Concrete Basics
Concrete is a mixture of Portland cement, coarse aggregate, sand, and water, to which
plasticizers and other admixtures can be added as required. Once concrete is mixed, it is placed
in forms, leveled, screeded, and finished to produce a concrete slab. All concrete surfaces emit
some degree of moisture as they cure. Too little moisture in the mix can disrupt the hydration
process and weaken the concrete by preventing it from curing properly. Too much moisture can
overwhelm the capacity of the hydration process and prevent the concrete from curing properly.
Concrete Porosity & Permeability
Poured concrete has capillaries, which give it a porous and permeable nature. The greatest
single factor affecting porosity in concrete is the water to cement ratio. Concrete needs only
.35 pounds of water for each pound of cement to fully cure to maximum strength. Any water
to cement ratio above this .35-1 ratio is called water of convenience. When the water of
convenience exceeds a .42-1 ratio, the spaces between the capillaries become larger, causing a
greater degree of permeability. The degree of porosity is also affected by placement and curing
methods used.
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Flooring Over Concrete Slabs
Moisture & Concrete Basics
Capillary Action
The process by which water (in the form of vapor) is moved from a lower elevation to a higher
elevation is directly affected by the porosity of the concrete mixture. Tight, densely mixed
concrete is highly resistant to moisture vapor transmission via capillary action. Over-watered
concrete will absorb moisture via capillary (wicking) action. This moisture (in the form of vapor)
will migrate through the concrete to the adhesive bond line of the floor covering material.
Excessive moisture emissions will attack flooring adhesives, causing buckling, warping and
delamination that destroys both the aesthetic appearance and the performance of the flooring
system.
Critical Saturation
Concrete slabs that are exposed to excessive amounts of moisture can reach a point of critical
saturation. At this point, the pores or capillaries of the concrete are no longer freely passing
water vapor, but are completely full of liquid. The point at which critical saturation is reached
will depend on the permeability of the concrete, but is typically seen around 12.0 lbs/1,000 sq.
ft/24 hrs.
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Flooring Over Concrete Slabs
Moisture & Concrete Basics
Other Sources of Water
In addition to the water used in the concrete
mixture, external water can enter and move through
the concrete slab via several mechanisms, including
lateral migration, leakage, and hydrostatic pressure.
Lateral Migration
Moisture can migrate laterally into a slab due
to pressure differences between the interior and
exterior environments. For example, as heated air
rises in the interior of the building, a negative
pressure is created at the level of the concrete
slab. Because water vapor will tend to move from
an area of high pressure to an area of low pressure,
moisture will be drawn up through the slab.
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Flooring Over Concrete Slabs
Moisture & Concrete Basics
Other Sources of Water Cont’d...
Leakage
Water will naturally travel from a higher elevation
to a lower elevation due to the force of gravity.
Uneven terrain or nearby hillsides can direct
substantial amounts of water toward concrete slabs.
Consistent over-watering of plant beds or raised
planters, plumbing leaks and roof leaks are also
common sources of excess water.
Hydrostatic Pressure
If the water table of the surrounding area is higher
than the level of a below-grade slab, the slab will be
subjected to hydrostatic pressure. The pressure of
this moving water causes moisture to be forced into
and through the concrete slab above.
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HYDROSTATIC PRESSURE
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Slide 9 of 56
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Flooring Over Concrete Slabs
Moisture & Concrete Basics
Curing Concrete
There are a number of factors that will affect the amount of time it takes for a concrete slab to
fully cure. Flooring systems installed over concrete slabs that have not been properly cured are
extremely likely to fail.
Water, Admixtures & Curing Compounds
The more water used in the mix, the more time the slab will take to cure. The use of various
admixtures can either slow or speed the curing process. Curing compounds will prevent water of
convenience from escaping and while assisting in concrete curing, will delay installation of the
floor covering for the same reasons.
Slab Thickness & Construction
Thicker slabs will require more time to cure than thinner slabs. Also, slabs poured on metal decks
or on low permeability membranes will take longer to cure than slabs poured on grade where
no vapor barrier is present.
Environmental Variations
Concrete slabs poured in the spring will tend to dry more rapidly than concrete slabs poured in
winter. Characteristics of the interior environment, such as temperature, ventilation and relative
humidity will also affect curing time.
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Flooring Over Concrete Slabs
Moisture & Concrete Basics
Concrete is Naturally Alkaline
Fresh concrete contains alkaline components which give it a high pH. These components may
be neutralized or leached out during the curing process, however when concrete is not cured
properly, these alkaline components remain in the concrete and cause its pH to remain high.
As water vapor passes through the concrete, the moisture will become alkaline and carry this
alkalinity to the concrete/flooring interface.
Flooring Failures are Related to Moisture and Alkalinity
Adhesives can be moisture resistant yet sensitive to alkaline attack. Flooring failures can
occur when emissions are low (3.5 lbs - 5.0 lbs), if pH is high. An adhesive resistant at 9.3 on
the pH scale may not be resistant to a pH of 9.6, which represents a three-fold increase in
alkalinity levels.
Please remember the word ALKALINITY. You will be required to enter it in order to proceed with the
online examination.
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Flooring Over Concrete Slabs
Moisture & Concrete Basics
Alkalinity Attacks Flooring Adhesives
As water vapor collects and condenses at the bond line of the adhesive, this newly liquefied
moisture is relatively neutral in pH. As this relatively “pure” moisture collects at the bond
line of the flooring system, the existing moisture in the concrete begins to move toward it
due to osmosis. As a result, the alkaline components in the concrete migrate to this area and
raise the alkalinity of the condensed moisture to pH levels of 11-13 or more. The condensed
moisture is transformed into a caustic solution that is harmful to virtually all types of
adhesives and will cause damage to, or adhesion problems with materials applied to the slab.
PH scale goes from 0 (acid) to 7 (neutral) to 14 (alkaline)
pH is a measure of the number of Hydrogen ions (acidity) or Hydroxide ions (alkalinity) in a
water-based system. pH is measured on a logarithmic scale from 0 (acid) to 7 (neutral) to 14
(alkaline). Because the pH scale is logarithmic, each point represents a ten-fold increase in
alkalinity (e.g. a pH of 10 is ten times more alkaline than a pH of 9). Most adhesive and floor
covering manufacturers will not allow installation of their materials if alkalinity is above 9.
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Slide 12 of 56
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Flooring Over Concrete Slabs
Moisture & Concrete Basics
Why does moisture need to be controlled?
All Concrete Surfaces Emit Some Degree of Moisture
Even concrete that is perfectly designed, screeded and finished will show moisture emissions
over the course of curing and drying of the concrete, whether above, below or on-grade.
Concrete Can Reach a Point of Critical Saturation
Concrete requires a water to cement ratio of .35 to 1. Any water above this ratio is referred to as
water of convenience. Too much water of convenience trapped in the slab will migrate through
to the flooring, seriously compromising the adhesive bond. Similarly, on-grade concrete, with no
vapor barrier in place (or a poorly constructed vapor barrier), may allow ground moisture to wick
through the porous concrete into the flooring environment, thereby causing potential bonding
problems with the floor covering material. Too much moisture present at the concrete/floor
covering interface may prevent proper curing of the floor covering adhesive.
Moisture Migration Can Cause High Levels of Alkalinity
Water passing through concrete is alkaline in nature and can degrade and emulsify virtually
every adhesive used in the floor covering industry. Concrete must be allowed to dry out as much
as possible prior to installation of floor covering materials.
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Flooring Over Concrete Slabs
Moisture & Concrete Basics
Where does moisture need to be controlled?
On-Grade and Below-Grade Surfaces
Below-grade slabs are exposed to moisture through lateral migration, hydrostatic pressure and
capillary action. These surfaces are in direct contact with the ground and, as such, water has a
direct contact point to the concrete allowing for penetration into the slab. On-grade slabs are
exposed to moisture through capillary action and diffusion.
Light Concrete Slabs/Above-Grade Surfaces
Even floors above grade can exhibit moisture emissions caused by residual water of convenience
in the concrete. This water is trapped between the non-perforated pan construction and a curing
compound placed on top of the concrete, thus leaving the water of convenience with no place
to go. Until that is, the flooring contractor starts troweling the floor covering adhesive, etching
the curing compound and allowing the water out of the concrete.
Moisture control is important for all types of concrete slabs regardless
of whether they are above-grade, on-grade or below-grade!
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Flooring Over Concrete Slabs
Moisture & Concrete Basics
Myth #1: Moisture Emissions Are Not A Concern With Old Concrete Slabs
Depending on the vapor barrier in place, the structure of the concrete, the design of the base
materials and the placement of the concrete, older, pre-existing concrete often shows high levels
of moisture emissions.
Myth #2: Moisture-Induced Flooring Failures Cannot Happen On Suspended Slabs
Some of the industry's greatest problems occur in suspended slabs with non-perforated steel pan
construction. The water of convenience in the concrete mix cannot escape, and is contained by
curing/sealing compounds applied to the surface. This water is released with the troweling of
the adhesive on the concrete. The escaping moisture can and will affect the adhesive bond line.
Myth #3: Moisture Problems Will Go Away Once A Building Acclimates
As a building is acclimated and brought under HVAC control, moisture emissions will actually
increase due to the relationships between concrete, pressure, temperature and humidity.
Consequently, it is important for a space to be acclimated under HVAC control and then the
concrete can be tested for moisture emissions. With a properly placed vapor barrier in place,
moisture emissions through the concrete should reduce with time.
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Slide 15 of 56
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Flooring Over Concrete Slabs
Flooring System Failures
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Flooring Over Concrete Slabs
Flooring System Failures
Excess Moisture and Alkalinity are Leading Causes of Flooring Failures
This figure exceeds all combined forms of failures including poor workmanship, asphaltic
(cutback) adhesive problems, manufacturing defects, and job-site related concerns. It is not
simply the migration of moisture through concrete or the presence of moisture in concrete that
causes flooring failures.
Most Slabs Show Moisture Emissions Greater Than 3 Pounds
Most flooring manufacturers warn against moisture emissions greater than 3-5 lbs. Flooring
manufacturers have moisture limitations for installation of their products, because flooring
materials tend to be non-breathable and may have extreme sensitivities to moisture and
alkalinity.
Repair Costs are 5X Greater Than Original Installation Costs
Installation of new homogeneous sheet vinyl flooring costs approximately $35.00/yd installed.
Removal of a failed floor covering due to concerns related to moisture vapor transmission will
cost far more to replace. This would include demolition of the existing floor, removal of the
adhesive, prep work and labor charges involved, remediation (moisture mitigation) of the
concrete as well as the cost of the new floor covering material.
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Flooring System Failures
Root Causes of Moisture Migration
No Vapor Barrier
Properly placed, ASTM-approved vapor barriers
prevent ground moisture from wicking into the
naturally porous concrete and provide the best
protection against moisture intrusion into the
concrete slab.
Fast Track Construction
Poorly prepared concrete, no vapor barrier in place,
breaks and punctures through the vapor barrier,
over-watered concrete, and curing/sealing
compounds, all serve to cause moisture emission
problems for the floor covering industry. In many
cases, job delays will force a General Contractor into
a premature installation of the floor covering
material prior to the manufacturer's installation
criteria for allowable moisture readings being met.
It is also not uncommon to find no vapor barrier in
place where one was actually specified.
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Flooring System Failures
Root Causes of Moisture Migration Cont’d…
Over-Watered Concrete/No Admix
When properly used, concrete admixes increase the flowability of concrete without requiring
additional water of convenience, allowing for a more thorough cure and much denser concrete.
Over-watered concrete increases the porosity/permeability of the concrete and results in greater
capillary action of moisture through the concrete.
Use of Curing Compounds
Water of convenience is necessary to place and finish concrete, yet must be allowed out to
prevent flooring failures. The water of convenience is often trapped under a highly polished
concrete surface and a curing/dusting compound, or sealer that is applied to the concrete during
construction. ASTM specifications and floor covering manufacturers mandate removal of the
curing compound prior to installation of the floor covering material.
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Flooring System Failures
Root Causes of Moisture Migration Cont’d…
Non-Breathable Flooring
Floor covering manufacturers have provided the
finest array of covering materials ever known.
However these materials, for the most part, do not
allow water or water vapor to pass through them.
This essentially traps moisture below the concrete.
Too much moisture emission can and will cause
adhesive bonding failure.
Alkaline Sensitive Latex Adhesives
The EPA and OSHA have severely restricted the use
of solvents and solvent-based materials in adhesives.
These solvents allowed adhesives to be highly
moisture resistant and not affected by moisture
migration through concrete. The new adhesives are
primarily latex based with little or no solvents.
Though somewhat moisture tolerant, they cannot
withstand the aggressive alkaline attack associated
with moisture migration through concrete.
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Flooring System Failures
Auxiliary Causes of Moisture Migration
Rain on Exposed Concrete
Without protection from the elements (i.e. properly
placed plastic sheeting during construction), a slab
will often absorb rain water into the surface of the
concrete. This absorbed water extends the drying
cycle of the concrete and may cause floor covering
bonding problems once released. This rain water
may also penetrate into the bedding material
beneath the concrete, causing tremendous problems
with moisture and capillary wicking action.
Landscaping/Poor Drainage
Side wall foundations and footers should have vapor
barrier draped completely over these construction
points, completely isolating the concrete from
moisture penetration. This will prevent water from
entering the concrete from landscaping concerns
and from rain and roof drainage.
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Flooring System Failures
Auxiliary Causes of Moisture Migration Cont’d…
Maintenance Issues
Over-maintenance, flooding of floors during cleaning, and improper usage of highly caustic
floor strippers can cause bonding problems between the floor covering and the concrete.
Building Use & Occupation
Topical spills, broken water pipes, roof leaks, water tracked in from outside of the facility,
and overflowing commodes, will all contribute moisture into the enclosed building
environment causing potential floor covering bonding failure.
Sweating & Dew Point
Environmental acclimation of a building space can often cause a differential between the
temperature and humidity of the concrete and flooring, causing conditions such as dew
point and condensation. This can allow moisture to collect on the surface of the concrete,
compromising the integrity of the floor covering bond. Proper monitoring of the internal
environment HVAC controls can greatly reduce the occurrence of this phenomenon.
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Flooring Over Concrete Slabs
Flooring System Failures
Warning Signs of Moisture & Alkalinity
The destructive effects of moisture and/or alkalinity
on a flooring adhesive may be visible within days of
installation. There are a number of warning signs
that are indicative of moisture and alkalinity
problems.
Concrete Expansion/Contraction
Expansion and contraction of the concrete can cause
cracks in the slab, allowing moisture to wick through
into the flooring environment.
Delamination/Bonding Loss
Alkalinity will cause re-emulsification of the
adhesive and the floor covering material will be
readily and easily removed from the concrete.
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Flooring Over Concrete Slabs
Flooring System Failures
Warning Signs of Moisture & Alkalinity
Staining/Efflorescence
Alkaline attack can cause certain floor coverings to
become discolored. Dissolved alkaline salts are often
deposited at the tile juncture after the moisture has
evaporated, leaving a white, granular film at the
junctures.
Bumps, Ridges, Bubbles
Typically associated with homogeneous sheet
materials where moisture/alkalinity conditions have
caused bonding loss. As traffic progresses across the
floor covering material, it will shift and cause these
noticeable problems. Adhesive, broken down by the
forces of alkalinity, may be moved by wheeled
traffic and cause humps under the floor covering
material.
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Flooring Over Concrete Slabs
Flooring System Failures
Warning Signs of Moisture & Alkalinity
Adhesive Deterioration
Often seen as adhesive "bleeding" or oozing from
under the tile at the tile junctures.
Contaminants, Odors
Water trapped under a floor covering material has a
decidedly pungent aroma, caused by the mixing of
harsh alkaline salts and re-emulsified adhesive.
Mold, Mildew, Bacteria
Mold and mildew are often present beneath a failed
floor covering material. These two dangerous and
potentially devastating concerns may cause
unacceptable indoor air quality concerns within a
facility and pose potential health hazards to the
workers within the facility.
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Slide 25 of 56
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Flooring Over Concrete Slabs
Flooring System Failures
Who is responsible for flooring system failures?
Flooring Manufacturers
Manufacturers typically provide very specific criteria regarding the installation of their
product, including sub-floor preparation, trowel size, ambient conditions, layout, and detail
work. They are NOT however responsible for the moisture migration/increased alkalinity in
the concrete when tested as such. They simply supply the material that has detailed
specifications for installation. For years, the architectural and design community has asked
for greater stain resistance, improved wear features, higher (or lower) gloss readings,
outstanding fire resistance, faster installation, greater color choices, and synthetic materials
that resemble natural materials. The resilient flooring manufacturer has provided all of
these, however, at the price of moisture and alkaline intolerance.
Adhesive Manufacturers
As mentioned previously in this syllabus, the adhesive manufacturer is under the strict
scrutiny and mandates of the OSHA and EPA. Adhesives are no longer heavy-duty, solventbased and moisture resistant. Today, they must be ecologically green, with low VOCs/HAPs,
non-flammable and, in most case, biodegradable. Once again, the new generation of latexbased adhesives have a significant problem with high alkalinity affecting the adhesive.
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Slide 26 of 56
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Flooring Over Concrete Slabs
Flooring System Failures
Who is responsible for flooring system failures?
Concrete Contractors
A concrete contractor must follow his contract specifications to the letter, including proper
placement and treatment of a suitable ASTM vapor barrier beneath the concrete. Overwatering concrete and punching holes in the vapor barrier to enable a fast setting of the
concrete for finishing only serve to cause further problems with the floor covering
installation.
Flooring Contractors
The flooring contractor is usually the first to be accused when a floor covering failure occurs.
The flooring contractor is many times the least culpable party involved as he technically
installed the flooring material in accordance with the terms of his contract. Far too often the
flooring contractor is blamed for the presence of moisture in the concrete during the testing
phase and is required to do something about it.
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Slide 27 of 56
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Flooring Over Concrete Slabs
Flooring System Failures
Who is responsible for flooring system failures?
General Contractors
It is the responsibility of the General Contractor to ensure that his subcontractors carry out all
phases of the building contract. It is his job to make sure that the concrete contractor utilizes the
proper mix ratio and follows accepted concrete practices. When a concrete slab is tested for
moisture vapor emissions and found to be high, the General Contractor may often times issue a
"waiver of installation" to the flooring contractor, despite the higher than allowable moisture
conditions. This is a band-aid solution to the problem; one that will fail down the road and
ultimately lead to enormous repair costs.
Architects/Specification Writers
By following industry accepted practices, the Architect or Specification Writer can dictate the
proper materials and practices to be used during a building's construction. Addressing the
concrete moisture migration issue during the formation of the plans will greatly reduce the
occurrence of moisture induced floor covering failures.
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Slide 28 of 56
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Flooring Over Concrete Slabs
Flooring System Failures
Myth #1: Hydrostatic Pressure Causes Flooring Failures
Hydrostatic pressure is the pressure or force exerted by water on a below-grade concrete
surface. The body of water (the ground water in this case) MUST be higher than the concrete
slab in order to exert hydrostatic pressure. Therefore, by definition, hydrostatic pressure cannot
affect an on-grade slab.
Myth #2: Built Up Vapor Pressure Causes Flooring Failures
This is not true, although alkaline salts can accumulate beneath a concrete surface and actually
contribute to erosion of the concrete.
Myth #3: Osmotic Pressure Causes Flooring Failures
Osmotic pressure does not affect adhesive bonded floor covering systems, although it can
sometimes occur with epoxy or urethane poured flooring.
Myth #4: Latex-Based Adhesives Are More Sensitive to Moisture Than Solvent-Based Adhesives
Latex-based adhesives, though somewhat less moisture resistant than solvent-based adhesives,
are definitely more susceptible to alkaline attack.
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Slide 29 of 56
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Flooring Over Concrete Slabs
Moisture & Alkalinity Testing
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Slide 30 of 56
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Flooring Over Concrete Slabs
Moisture & Alkalinity Testing
Calcium Chloride Crystal Test
The calcium chloride crystal test (ASTM F-1869-03)
is the industry accepted standard for providing a
quantitative measure of moisture vapor transmission
levels through a concrete slab. It is non-destructive,
easy to use and provides for an accurate assessment
of a facility's concrete moisture migration.
The test measures changes in the weight of moisture
absorbing crystals exposed to concrete for specific
lengths of time. The test determines the weight of
the emitted moisture as it would occur over a 1,000
sq. ft. slab during a 24 hr period (e.g. 3.0 lbs/1,000
sq. ft./24 hrs). Proper testing is critical and will
produce a quantitative representation of actual
amounts of moisture emitted by a concrete slab.
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Flooring Over Concrete Slabs
Moisture & Alkalinity Testing
Relative Humidity Probe
The relative humidity probe (ASTM F-2170-02) is
a new procedure, adapted from the well used
European standard. This test utilizes an electronic
probe placed into pre-drilled holes in the concrete.
It measures the relative humidity of the concrete
and can be used to analyze the overall curing rate
of the concrete from placement to final cure. The
figures obtained cannot be correlated with results
from calcium chloride tests and must be evaluated
independently as most floor covering manufacturers
do not specify this test method.
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Slide 32 of 56
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Flooring Over Concrete Slabs
Moisture & Alkalinity Testing
pH Testing
Virtually every major adhesive and floor covering manufacturer requires pH testing of concrete
prior to installation of their materials. There are several ways to measure the pH of concrete,
including electronic probes/meters, litmus paper, and pH pencils. Electronic probes have the
greatest degree of accuracy, however they are expensive and are not readily available to
Flooring Contractors or General Contractors. The litmus paper test is not a true or accurate
assessment of the alkalinity of the concrete. The pH pencil is the industry accepted standard and
measures accurately the pH present at the surface of the concrete. In order to use the pH pencil
test, an area of the slab is marked with an X using a pH pencil and a few drops of distilled water
are added to the X. After a period of 15 seconds, the color of the X is compared to a color chart.
The color that most closely matches the X provides the pH reading.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
ß pH 8 to 13 will destroy adhesives à
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Flooring Over Concrete Slabs
Moisture & Alkalinity Testing
Who is responsible for moisture and alkalinity testing?
Flooring Contractors
Although floor covering manufacturers require moisture testing prior to installation of the
floor covering, it is often times left to the flooring contractor, who in turn gets blamed when
higher than allowable moisture migration readings are discovered. The flooring contractor
should not be the sole party responsible for determining whether the concrete is acceptable
for floor covering installation.
Testing Firms
Architects should always specify an independent consulting or testing firm. Independent
testing firms are highly skilled professionals who will accurately report moisture migration
levels from the concrete without prejudice or bias. If the concrete has unacceptable levels,
it will be clearly pointed out prior to the installation of any floor covering material.
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Flooring Over Concrete Slabs
Moisture & Alkalinity Testing
Who is responsible for moisture and alkalinity testing?
General Contractors
The General Contractor and Flooring Contractor should jointly agree whether floor
conditions are acceptable for installation. Many times it is left solely up to the flooring
contractor to begin installation on a project. This should be a joint agreement between the
General Contractor and the Flooring Contractor after moisture testing has been performed.
Architects/Specification Writers
The architect or specification writer is the key to a well-written moisture testing
specification. Detail specifically in the plans and contracts when and where concrete moisture
testing is to take place, stating who the responsible party will be. Do not write generic
specifications citing the flooring manufacturers guidelines for installation. Be specific as to
the testing and responsible party thereof.
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Flooring Over Concrete Slabs
Moisture & Alkalinity Solutions
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Flooring Over Concrete Slabs
Moisture & Alkalinity Solutions
There are several options for dealing with concrete
slabs where independent testing has determined
that moisture emissions and/or alkalinity levels are
too high to safely install the desired floor covering.
1. Leave Concrete Exposed
Leaving the concrete unfinished will allow excess
moisture to evaporate into the air. Realistically
however, this may not be a viable solution in
instances where a high-performance homogenous
floor covering is specified, or where the intended
use of building precludes an unfinished floor.
2. Continue Curing Concrete
Allowing the concrete to continue curing is one of
the best options for dealing with excess moisture
and alkalinity problems. Unfortunately, waiting for
a concrete slab to cure for an extended period of
time may interfere with the construction deadlines
of the project.
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Flooring Over Concrete Slabs
Moisture & Alkalinity Solutions
3. Specify Breathable Flooring System
Specifying a breathable flooring system will allow
moisture emissions to pass through the floor
covering, however this may not be a viable option
for certain types of facilities. For instance,
breathable flooring systems may not meet the
health requirements of medical or health facilities.
Also, breathable floor coverings may not be
compatible with the aesthetics of the project.
4. Mitigate Moisture Migration
Various systems are available that mitigate the
migration of moisture through the slab. One type of
system prevents floor covering failure by preventing
water from migrating into the concrete from the
ground (e.g. vapor barriers). Another type of system
prevents floor system failures by mitigating moisture
vapor emissions from the concrete once it has been
placed and screeded, and is ready for floor covering
installation (e.g adhesive and primer systems).
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Moisture & Alkalinity Solutions
Mitigating Moisture During Construction
There are a number of measures that can be taken during the construction phase
of the project in order to minimize subsequent moisture migration problems and
flooring system failures.
Follow Industry Accepted Standards
The American Concrete Institute (ACI) has established a set of methods and practices that must
be followed in order to provide for the best concrete possible. Referencing proper ASTM
methods and recommendations will also serve to ensure a properly mixed, placed, screeded and
finished concrete slab.
Install Vapor Barrier Below Concrete
It is important to use vapor barriers that comply with ACI Committee 302. Vapor barriers should
be installed double-lapped, below the concrete slab and proper attention given to treatment of
protrusions, pipes and flanges through the vapor barrier (Refer to chart on next slide for proper
placement of a suitable vapor barrier prior to pouring and placement of the concrete). Usage of
a high strength polyolefin vapor barrier at least 10 mils or thicker is preferred.
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Moisture & Alkalinity Solutions
Vapor Barrier Placement
This chart can help you determine the
correct placement of the vapor barrier
based on the specifics of your project.
In some cases, if your project does not
have a vapor-sensitive covering or a
humidity controlled area, a vapor barrier
may not be required (See Figure 1).
In other cases, the vapor barrier should
be installed under the concrete slab,
either above a layer of granular material
(See Figure 2) or below a layer of dry
granular material (See Figure 3).
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Moisture & Alkalinity Solutions
Mitigating Moisture During Construction Cont’d…
Using Concrete Admixtures
While the use of admixtures, such as superplasticizers, in concrete has not shown any
documented improvements in the strength of placed concrete, admixtures can help to reduce
the water to cement ratio. This provides for a denser concrete, while maintaining the flowability
of the concrete mix. The use of concrete admixtures helps to reduce the amount of water of
convenience that is required to properly place and finish the concrete slab.
Restrict Usage of Curing Compounds
The use of curing or sealing compounds has become commonplace when pouring concrete,
however their use can severely restrict the required evaporation and drying out of the water of
convenience in the concrete. This may contribute to failure of the floor covering materials at a
later date. Curing and/or sealing compounds may also hinder bonding of the floor covering
adhesive to the concrete. Wet-curing methods should be considered in lieu of curing and sealing
compounds when working with newly placed concrete.
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Moisture & Alkalinity Solutions
In-situ Repair Systems
Once a concrete slab has been poured and cured, there are additional measures that
can be taken to mitigate high moisture emissions and allow for flooring installation.
Topical Coatings
A thin paint-like coating is applied to the surface of the concrete and sets up a semi-permeable
membrane, essentially blocking some of the moisture emanating from the concrete. These
coatings are pH intolerant and cannot be used when the concrete pH level is above 9. The
instructions on usage call for neutralizing the concrete pH by washing the concrete with muriatic
acid to remove the alkalinity. This poses two fundamental problems: 1) exposure of an interior
space about to be finished to muriatic acid, as well as neutralizing solutions and copious water
for rinsing the acid off, and 2) the pH of the concrete will only be negated for a brief period of
time. These coatings claim to encapsulate and isolate existing adhesives including asphalt-based
adhesives. If the asphalt adhesive delaminates from the concrete, the new floor covering and
adhesive come up as well.
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Moisture & Alkalinity Solutions
In-situ Repair Systems Cont’d...
Silicates/Penetrants
Based on potassium or sodium meta-silicates, these low-solids, water-based, clear materials, react
with the alkaline material in the concrete to form a gel like structure. They claim to penetrate
deeply into the concrete, yet actual penetration is less than ¼" in most cases, due to the
immediate reaction and gel crystallization. The resulting gel continues to increase in size
whenever alkaline moisture is present, potentially causing devastating spalling damage to the
top layer of the concrete.
Thermosetting Materials
These are heavy duty reactive coatings applied to a shot-blasted floor that prevent and limit the
amount of moisture vapor transmission that enters the flooring environment. They can
effectively reduce the moisture vapor transmission levels from the concrete. This type of system
is one of the most expensive available for moisture protection and will range from $5.00 to
$10.00 per square foot completely installed. Blistering can occur if the epoxy material is not
specifically designed as a moisture limiting system, or if the epoxy material is applied improperly
or to a dirty substrate.
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Moisture & Alkalinity Solutions
In-situ Repair Systems Cont’d...
Membrane Systems
An effective means of limiting moisture vapor emissions from concrete, these systems utilize a
fiberglass mat and either acrylic or epoxy bonding agents/coatings to bond the system to the
concrete substrate. Moisture vapor emissions are restricted but not blocked from escaping. A
typical membrane system will reduce vapor transmission through the concrete by 70%-75%, by
trapping moisture emissions in the fiberglass mat and allowing them to wick across the floor and
be reabsorbed back into the concrete. It is important to select a membrane system that does not
incorporate any silicate materials as the primary basis of negating moisture vapor emissions.
Adhesive & Primer Systems
This type of system is designed to block low-level moisture emissions while negating the
damaging effects of alkalinity. A high-solids, acrylic primer is applied to the porous concrete, and
after proper dry time, the required adhesive system suitable for the respective floor covering is
used to bond the floor covering to the concrete. It is the most cost effective, simple to use and
contractor friendly system available, with moisture protection levels up to 8lbs/1000 sq. ft./24 hrs.
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Flooring Over Concrete Slabs
Specifications
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Specifications
Vapor Barriers
•
Specify an ACI Committee 302 approved lowpermeability vapor barrier that is puncture
resistance and at least 10 mils thick. If the vapor
barrier is to be subjected to direct traffic from
construction vehicles and concrete placement
equipment, specify a vapor barrier at least 15
mils thick.
•
Follow ACI recommendations for placement of
the vapor barrier depending on floor covering
materials and roofing work to be performed.
Prevent moisture intrusion into the concrete
slab by protecting with roof system as quickly
as possible.
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Specifications
Concrete Slabs
•
Prepare construction documents in accordance with ASTM practices for testing and
preparation of the concrete for installation of floor covering materials. Specify independent
moisture testing to be done prior to installation of flooring materials.
•
Follow ACI guidelines for concrete mix design, placement, and curing. Use admixes as
necessary to increase flow and placement without adding extra water of convenience.
•
Whenever possible, specify wet curing methods in lieu of curing compounds for concrete.
Curing compounds may adversely affect drying time and bond performance of floor
covering adhesives.
•
Use a capillary break layer beneath the concrete. This is a layer of coarse gravel or crushed
stone that will interrupt the movement of water via capillary action from the ground
upwards into the concrete slab.
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Specifications
Moisture Mitigation Systems
•
Refer to the flooring manufacturer's specifications for installation requirements and
moisture and alkalinity recommendations. If moisture emission levels exceed the flooring
manufacturer's tolerances, specify a moisture mitigation system. Investigate which types of
flooring products can be used with which systems.
•
Evaluate the costs and installation criteria for the chosen moisture mitigation system. It is
often easier and less expensive to specify a moisture mitigation system for floor covering
materials as part of the overall construction package, rather than as a separate add-on or
change order.
•
Investigate moisture protection systems based on longevity of the manufacturer, product
warranty, level of protection, and success rate of materials. Require the manufacturer of the
moisture protection system to have at least 10 years of experience in manufacturing the
product and at least 3 years in product installations.
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Specifications
Moisture Mitigation Systems Cont’d…
•
Require the manufacturer to provide documented records of successful installations, as
well as insurance documentation and coverage in the event of a job site failure. The
manufacturer should also provide detailed specifications in accordance with standard CSI
formats and architectural standards.
•
Many moisture protection manufacturers do not specialize in moisture mitigation, but
rather have added programs and/or divisions that incorporate this feature. Several
moisture protection products available today are generic, privately labeled materials,
designed as a blanket approach to moisture mitigation and protection.
•
Many moisture protection materials appear to be an inexpensive solution up front,
however, when moisture induced failures occur, the cost to repair or replace the floor
covering material is many times more expensive than the original cost.
•
Confirm that local trades are capable and trained to install the specific moisture protection
system that you have chosen.
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Flooring Over Concrete Slabs
Course Summary
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Course Summary
Moisture and Concrete Basics
•
Concrete is a mixture of Portland cement, coarse aggregate, sand, and water, to which
plasticizers and other admixtures can be added as required. Excess water, or water of
convenience, results in concrete with increased porosity and permeability.
•
Water can enter a concrete slab via capillary action where water is drawn up through the
pores of the concrete, ultimately reaching the adhesive and the flooring material. Concrete
slabs are also exposed to water via lateral migration, leakage and hydrostatic pressure.
•
Concrete slabs that are exposed to excessive amounts of moisture can reach a point of
critical saturation. At this point, the pores or capillaries of the concrete are no longer freely
passing water vapor, but are completely full of liquid.
•
If concrete is not cured properly, alkaline components will remain in the slab and cause it to
have a high pH. As water vapor passes through the concrete, the moisture will carry this
alkalinity to the concrete/flooring interface where it will degrade and emulsify the adhesive.
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Course Summary
Flooring System Failures
•
Excess moisture and alkalinity are the leading cause of flooring system failures in the United
States. Flooring failures can occur on below-grade, on-grade, and above-grade concrete
slabs. Remedial costs can exceed 5 times the cost of the original floor covering installation.
•
Root causes of moisture migration include poorly prepared concrete, no vapor barrier,
breaks and punctures through the vapor barrier, over-watered concrete, curing/sealing
compounds, the use of non-breathable flooring, and alkaline sensitive adhesives.
•
Moisture migration can also result from auxiliary causes such as rain on exposed concrete
slabs, landscaping, poor drainage, maintenance issues, building use and occupation, or
sweating and dew point as a result of HVAC malfunctions.
•
Warning signs of moisture and alkalinity include concrete expansion or contraction,
delamination of flooring materials, bonding loss, adhesive deterioration, staining,
efflorescence, bumps, ridges, bubbles, contaminants, odors, mold, mildew, and bacteria.
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Course Summary
Moisture and Alkalinity Testing
•
The calcium chloride crystal test (ASTM F-1869-03) is the industry accepted standard for
providing a quantitative measure of moisture emissions through a concrete slab. The test
measures changes in the weight of moisture absorbing crystals exposed to concrete for a
specific period of time.
•
The relative humidity probe (ASTM F-2170-02) is a new procedure, adapted from European
standards. This test utilizes an electronic probe placed into pre-drilled holes in the concrete
and measures the relative humidity of the concrete. It can be used to analyze the overall
curing rate of the concrete from placement to final cure.
•
The pH pencil is the industry accepted standard for accurately measuring the pH present at
the surface of a concrete slab. The slab is marked with an X using the pH pencil and, after
the addition of some distilled water, the color of the X is compared to a pH color chart.
•
It is the responsibility of the architect to specify independent moisture and alkalinity testing.
Once testing is completed, the General Contractor and Flooring Contractor should jointly
agree whether floor conditions are acceptable for installation.
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Course Summary
Moisture and Alkalinity Solutions
•
If independent testing has determined that moisture emissions and/or alkalinity levels are
too high to safely install the desired floor covering, options include leaving the concrete
exposed, allowing the concrete to continue to cure, specifying a breathable floor system,
or specifying a moisture mitigation system.
•
Once a concrete slab has been poured and cured, there are additional measures that can be
taken to mitigate high moisture emissions and allow for flooring installation. These options
include the use of topical coatings, silicates or penetrants, thermosetting materials,
membrane systems, or adhesive and primer systems.
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Course Summary
Specifications
•
Be sure to specify a low-permeability vapor barrier that is puncture resistance and at least
10 mils thick. Specify a 15 mil vapor barrier if it is to be subjected to direct traffic from
construction vehicles or concrete placement equipment.
•
Follow ACI guidelines for concrete mix design, placement, and curing. Use admixes as
necessary to reduce the need for additional water of convenience. Ensure that independent
moisture testing is performed prior to the installation of flooring materials.
•
Moisture can be mitigated during the construction process by installing a vapor barrier
beneath the concrete slab and ensuring that the concrete is properly mixed, placed, and
cured. Admixtures can help reduce the need for water of convenience. Wet-curing methods
should be considered in lieu of the use of curing compounds.
•
Ensure that the manufacturer of the chosen moisture mitigation system has at least 10 years
of experience in manufacturing the product and at least 3 years in product installations, as
well as documented records of successful installations and insurance coverage.
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Conclusion of This Program
•
AEC Daily Corporation is a Registered provider with the
AIA Continuing Education Systems. Credit earned upon
completion of this program will be reported to CES
Records for AIA members.
•
If you desire AIA/CES, CSI and/or state licensing
continuing education credits, please click on the button
below to commence your online examination. Upon
successful (80% or better) completion of the exam,
please print your Certificate of Completion.
©2004 Sealflex Industries, Inc. The material
contained in this course was researched,
assembled, and produced by Sealflex
Industries, Inc. and remains their property.
Questions or concerns about this course
should be directed to the instructor.
•
For additional knowledge and post-seminar assistance,
please visit the Seminar Discussion Forum (click on the
link above and bookmark it in your browser).
•
If you have colleagues that might benefit from this
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