Dynamics of Concrete Moisture Vapor Emissions
Moisture as a liquid or as a vapor is constantly in motion. Moisture vapor is a mixture of air and water. This form of moisture vapor is transmitted from one area to another by the physical laws of gasses and chemical equilibrium or in other words, whenever a difference of vapor pressure exists. Within a facility during a controlled climate (HVAC), the temperature in the room is usually 70° to 80° F and the relative humidity is 30% to 50%. The concrete slabs are typically cooler with a higher level of humidity. Physics has proven that the air above the slabs attempts to draw the moisture out of the concrete to equalize pressure even though this dynamic of equilibrium never seems to fully stabilize or complete itself. Moisture vapor emission is capable of penetrating through slabs where water in a liquid form oftentimes cannot. Capillaries (microscopic voids) within the concrete slab may be small enough to keep physical water from transmitting through but moisture in a vapor form can freely move to the surface of the slab.
By comparing the vapor pressure in fluctuating environments, one can estimate the movement of vapor pressure through concrete. However, in reality vapor emission levels are complex due to variations in temperature, humidity, permeability and flow path through the concrete. For these reasons vapor emissions may be measured but cannot be accurately calculated, making it very difficult to predict possible future floor failure.
Moisture presence in concrete always carries soluble and insoluble salts. The most common are sodium chloride, calcium sulfate, calcium carbonate, and magnesium sulfate. These salts cause a high alkalinity level that is detrimental to floor covering. Salts come from air, aggregate, design mix water, rainwater, salt-charged ground water, and from sodium and calcium chloride. When water in a saline (salt) solution evaporates, salt crystals are formed - a process known as efflorescence. As moisture vapor moves towards the warmer room above, it brings salts to the surface of the slab and salt deposits will accumulate. This efflorescence at the bond line of the floor covering will eventually cause the adhesive to break down and re-emulsify causing floor covering failure.
Commonly Known Facts:
- All concrete is permeable
- Vapor emissions can be measured, but not accurately calculated
- Water, whether liquid or vapor, always seeks the path of least resistance
- There is a significant difference between moisture content and moisture movement
- Moisture must be present in hardened concrete for the continued gain of strength and other desired properties, this moisture may remain in the concrete for many years
- Healthy new concrete is alkaline, pH of 12.5 or more. Once cured and dried, surface alkalinity through carbonation drops to normal (neutral) range. But the alkaline within the concrete will continue to be, pH of 12.5 for the life of the concrete
- Common sources of moisture as it relates to floor covering failure is too much ground water and moisture within the concrete
- Moisture does not travel laterally in concrete
- As a liquid or as a vapor, moisture is constantly in motion
Testing Interior Concrete Slabs
Calcium Chloride Testing
The Calcium Chloride test method covers the quantitave determination of the rate of moisture vapor emitted from below-grade, on-grade and above-grade (suspended) concrete floors. The quantity of moisture is expressed as the rate of moisture vapor emissions, measured in pounds of moisture over 1000 square foot area during a 24-hr period.
The Calcium Chloride test method is used to obtain a quanitive value indicating the rate of moisture vapor emission from a concrete floor and whether or not the floor is acceptable to receive resilient floor covering. The procedures for proper Calcium Chloride testing are found in ASTM F 1869.
The moisture vapor emissions rate only reflects the condition of the concrete floor at the time of the test. All concrete floors emit some amount of moisture in vapor form. Concrete moisture emission is a natural process driven by environmental conditions. Moisture vapor can change based on the tempature and humidity of the interior and exterior of the room being tested. Moisture vapor emission test results cannot guarantee floors from failing unless the slabs are sealed with a permanent penetrating moisture vapor emission control system.
pH Testing
If you performed a pH test on just about any concrete slab by breaking it in half and testing the center of it you would find it to be high in pH (ASTM F 710, X1.4 Alkalinity). Alkali content is a natural occurrence in concrete and becomes a problem when the alkaline salts (pH) migrate to the surface and interfere with the bonding capability of adhesives to the slab surfaces. Alkaline salts carried within moisture that is transmitted from the ground through the slabs or directly from the slabs themselves either on grade, below grade or above grade have a tendency to prevent or destroy satisfactory bonding of adhesives by sheer physical displacement and by separating the polymers in the glue. They can leave unsightly salt deposits at the seams of sheet materials and joints of tiles. They can also have a deteriorating effect on the overall installation.
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pH 7 (neutral concrete surface condition) |
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Concrete floors should be tested for alkalinity before the installation of resilient flooring. The pH scale runs from 1 to 14, with 7 being neutral. Below 7 is considered acidic while above 7 is alkaline. When testing for pH, the allowable readings for the installation of resilient flooring are 6 to 9 on the pH scale.
The most accepted form of testing is the use of a wide-range pH paper, along with a pH chart and distilled or de-ionized water. The ASTM F 710 “Preparing Concrete Floors to Receive Resilient Flooring” details the procedure to perform pH testing in section 5.3.1.
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pH 13
(high in alkalinity) |
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ASTM F 710 – (Testing Procedures, 5.3.1) – states the following:
“To test for pH at the surface of a concrete slab, use wide range pH paper, its associated pH chart, and distilled or deionized water. Place several drops of water on a clean surface of concrete, forming a puddle approximately 1 in. (25 mm) in diameter. Allow the puddle to set for 60+ 5 s, and then dip paper into the water. Remove immediately, and compare to chart to determine pH reading.”
Ideal Jobsite Conditions for Successful Flooring
- Follow all flooring material manufacturer’s recommendations regarding the successful installation procedures of the new proposed flooring.
- Acclimate the room per flooring manufacturer’s recommendations regarding temperature, humidity and dew point prior to installing flooring materials.
- CS2000 is a full penetrating sealer that creates a crystalline barrier inside the top portion of the concrete substrate. Any concrete surface removal more than 1/16th inch will have to be re-treated with Creteseal CS2000. Any trench work will also have to be re-treated. Please notify Creteseal for proper remediation of the concrete that has been affected.
- Prior to the installation of new flooring, fully clean the concrete of all construction debris, contaminates, cleaning solutions, paints, solvents and other materials that might interfere with the proper adhesion of the finished for covering.
- Use only flooring adhesive made by or recommended by the same finish-flooring manufacturer.
- Always consider the intended use of the flooring system and environment including weight and traffic of the facility when selecting your appropriate flooring and adhesive.
- V-groove all cracks, control joints and construction joints ¼ “wide 5/8” deep and fully fill with ARDEX SD-F Feather Finish. Joint filler can include epoxy for use in high water table areas provided it is compatible for use with the new flooring. Gypsum material is not allowed. Cracks, control joints and construction joints that are not addressed properly will not be covered under the Ceteseal 15-Year Warranty.
Concrete sawcuts, expansion joints, cold joints and cracks must be treated properly to protect any flooring system. This area of construction is commonly overlooked or treated as insignificant. Floor failures oftentimes fall back on this area of negligence and cause owners, architects and the builder much pain financially. This disruption also causes delays in schedules not being met for completion.
The following diagram and procedure is an aid designed to protect all parties involved with finishing the flooring system in order to meet intense scheduling as well as delivering on time processing.
Creteseal Sketch for Treatment of Saw cuts/Joints/Cracks
Creteseal Specifications for the treatment of concrete saw cuts / joints
/ cracks
- Allow at least 56 days after the concrete has been poured for minimum
concrete dry-shrinkage / settling to occur.
- Clean out, mechanically v-groove as necessary all concrete saw cuts,
joints, and cracks to a minimum of ¼ inch WIDTH and 5/8 inch DEPTH
(you may open up wider & deeper).
- Vacuum the concrete saw cuts, joints, and cracks clean in preparation
for patching compound.
- Completely fill all saw cuts, joints and cracks level to the top of
the concrete surface. Fill all saw cuts, joints and cracks with Ardex
SD-F Feather Finish patching compound to a minimum DEPTH of 5/8 inch & ¼ inch
WIDTH.
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