Water, the silent foe.
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“Our
bodies need water to survive ... but water is a premature death
sentence
As a porous surface, concrete wicks water. Concrete substrates that do not have adequate drainage away from the slab, are below grade such as basements, those on grade that do not have adequate drainage, or possibly even compromised moisture barriers beneath the slab are all prime candidates for excessive rising moisture. Certain regions of the country having consistently high ground water tables and/or seasonal periods of continuous rain must also go the extra yard as to properly performing proven testing methods prior to ever sealing a decorative/architectural concrete surface. The ability of sealers to maintain their clarity; as well as resist defects such as blistering, pealing, flaking loss of bond, gassing bubbles, and efflorescence issues are directly associated with excess rising moisture. This article relates to how to identify and address these issues. It is my sincere hope that it provides you with answers to many of your questions and concerns; thereby, bringing about a greater degree of successful applications in your world of decorative concrete. Common Testing Methods and Metering Devices Plastic Sheet Method… Securely tape an 18” x 18” square of clear plastic on all 4 sides over the concrete. Wait 12-16 hours. Check for condensation. If condensation is found on the underside of the plastic or on the concrete, the concrete should be deemed to wet to be sealed. Note: in cooler temperatures (ambient/air or surface) the concrete may retain its moisture and fail to build up under the plastic. Highly recommend that you perform two different rising moisture/vapor testing methods … especially if there was any sign of moisture under the clear plastic. Calcium Chloride Test… Calcium Chloride Test measures the degree of water vapor emission rising out of a concrete slab over time. This test is specified by a majority of floor coating, sealing, and specialty resurfacing system manufacturers. Testing will provide readings, as related to lbs. (pounds) of moisture/vapor being emitted out 1,000 sq.ft. of concrete during a 24 hour period. For testing your will need a gram weight scale with a gradation of 1/10th (0.1) gram. Calcium chloride, in a pressured amount, is placed in a dish. Clear plastic is tented over it, being secured to the concrete. The calcium chloride is weighed before, and after the test (24 hours later). The resulting gain in lbs. (pounds) will equate to the amount of moisture. Extremely wet, saturated concrete, can sometimes result in readings well over 10 to 15 lbs per 1000 sq.ft. in 24 hours. The industry norm dictates that the moisture/vapor emission rate should not exceed 3 lbs per 1000 sq.ft. Note: One source for pre-measured, ready to use, Calcium Chloride Test Kits can be found on www.vaportest.com ASTM Standards & Practices for Calcium Chloride Testing are… E-1907-97 E-1869-03 E-l907-97 Electronic Moisture Meters… These meters read moisture content immediately. Detects moisture beneath the surface by measuring the resistance between two low frequency signals transmitted from conductive pads on the base of the instrument. One brand of electronic moisture meter is “The Tramex Moisture Encounter.” Relative Humidity (RH) Test… Method utilizes an instrument that measures relative humidity under a insulated box placed on the surface of the concrete. Test is performed by sealing the insulated box to the concrete and measuring the relative humidity inside the box with a capacitance-based humidity gauge. If the moisture inside the box measures less than 75%, the moisture content of the concrete is deemed to be less than 5%. Note: the air inside the box must stabilize for 12 hours prior to testing. Another method is to drill a hole in the concrete and place a special plug in it. The probe of a humidity gauge is inserted into the plug and left to stabilize for 12 hours. RH reading is taken. The advantage of this method is that the RH measurement is not effected by sealers, curing agents, or coatings on the concrete.
Excessive rising moisture being emitted from concrete typically exhibits itself on sealed surfaces in the form of outgassing, being even more prevalent in cases where sealer was applied as concrete substrate warms. Other signs include blistering, pealing, loss of clarity, darkening of substrate beneath sealer, efflorescence issues, and worst scenario being total bond failure. Water will migrate to the surface when there is higher vapor pressure in the concrete than in the air above the surface. This condition is more apt to occur when the air conditioning is first turned on in a new building; therefore, it is best to allow the air in the building to stabilize for a minimum of 24 hours before sealing an interior surface. Methods of Removing Moisture from Concrete Substrates In cases where there has been flooding, excessive rising moisture/vapors due to long periods of rain which result in ground saturation, or other temporary conditions is by using a “dehumidifier.” This equipment is quire effective for drawing the moisture up out of the concrete. When combined with the other methods listed below the results will be more rapid. Heat is another viable method for drying. Evaporation rates accelerate as temperatures rises, drawing the he moisture in the concrete to the surface, allowing evaporation to take place. Note: do not use direct fired heaters since they produce moisture due to combustion. Circulating air, when combined with any/or all the above, being blown over the surface is recommended; as is ventilation if possible. The above methods will only produce solutions if the rising moisture emissions are determined not to be continuous. Standard rising moisture/vapor testing methods should always be performed to assure that the concrete is within acceptable limits, being not more than 3 lbs. per 1000 sq.ft. over 24 hours. Conclusion Accurate testing of all concrete surfaces, as related to rising moisture/vapors is imperative in order to assure successful outcomes as related to adhesion, clarity, appearance, and longevity of sealers. Doing so will enable you to select the proper type/formulation of sealer in order to achieve maximum bond, cured out properties, and performance characteristics. Vapor permeable sealers allow for a certain degree of water/vapor emission; however, they should never be construed as to having the ability to withstand those which tested out to be excessive per industry standard. In cases where the rising moisture/vapors being emitted are deemed to be continuous, and/or exceeds the 3 lbs per 1000 sq.ft. over 24 hour period, there are potential solutions such as: crystalline waterproofing systems that form a gel in the capillaries of the concrete as rising moisture comes in contact with them (some even able to withstand hydrostatic pressure), as well as custom formulated impregnators. These modern chemically engineered products/materials are capable of deterring, or even in certain instances preventing, rising moisture from reaching the surface. You will want to test/evaluate their compatibility with any decorative concrete sealers you plan to apply over them. Generally speaking, there are those that can be used prior to application of polymer modified cementitious systems/overlayments, but again you must test for compatibility first. Lindy
(Lynn) Ausburne Copyright © 2005 Decosup Inc. All rights reserved. No portion of this article may be reproduced without the express consent or permission of Lindy Ausburne and Decosup Inc. | Home | Products Page | Decorative Concrete Gallery | Training | Technical Data | About us |
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