The cold, hard truth on coatings for concrete: Chemistry can be crucial to success or failure
From JAC, July 2005
| by Jayson Helsel |
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Concrete is seeing increasing use as a building material in construction. Successfully coating concrete, however, can pose many challenges....
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Tagged categories:
Blistering;
Coating selection;
Concrete
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Comment from Daniel Reed, (7/18/2011, 8:25 AM)
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In a paint recoating project what is the best way to evaluate the breathability of the coating system after it has had a second paint application years later? What criteria can we use to predict when the original coating should be removed because of the reduced permeability caused by subsequent coating applications?
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Comment from Glenn Summers, (7/19/2011, 7:06 PM)
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Good article concerning proper selection of a coating to meet the service requirements. To often the specifier does not consider how unstable a concrete is for years after it is placed. We take the approach of Stabilizing a concrete immediately after the inital set. Moisture travels in and out of concrete unless it is properly sealed to prevent moisture problems. Moisture within the matrix will migrate out to the surafce and collect at the coating-concrete interface. Alkali burn is common as well as saponification to collect behind the coating and cause it to disbond. A Stable Concrete does not allow moisture to come out and conditions such as efflorescence,Carbonation,DEF, ASR are not allowed to react to an atmosphere at the surface. Conversely this same sealer does not allow contaminates to enter the matrix to set up an environment for corrosion cell formation on embedded steel members. Keeping this Stable interior maintains the high pH intact preserving the passivating layer surrounding the reinforcing steel. The product I use is also extremely low VOC content for use in occupied living space and assures an excellent bond of all flooring/tile adhesives.
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Comment from Glenn Summers, (7/19/2011, 7:06 PM)
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Good article concerning proper selection of a coating to meet the service requirements. To often the specifier does not consider how unstable a concrete is for years after it is placed. We take the approach of Stabilizing a concrete immediately after the inital set. Moisture travels in and out of concrete unless it is properly sealed to prevent moisture problems. Moisture within the matrix will migrate out to the surafce and collect at the coating-concrete interface. Alkali burn is common as well as saponification to collect behind the coating and cause it to disbond. A Stable Concrete does not allow moisture to come out and conditions such as efflorescence,Carbonation,DEF, ASR are not allowed to react to an atmosphere at the surface. Conversely this same sealer does not allow contaminates to enter the matrix to set up an environment for corrosion cell formation on embedded steel members. Keeping this Stable interior maintains the high pH intact preserving the passivating layer surrounding the reinforcing steel. The product I use is also extremely low VOC content for use in occupied living space and assures an excellent bond of all flooring/tile adhesives.
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Comment from Jay Helsel, (7/19/2011, 9:17 PM)
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The question concerning recoating is a good one - and difficult to answer since there are many factors involved, such as the type of coating, thickness, and moisture conditions in the service environment. Coating manufacturers can be consulted concerning specifics with their coatings, but we are currently involved in laboratory testing that may provide an answer. The goal of the test program is to establish a protocol that can eventually be used to determine the number of times that a given system can be repainted before the reduction in permeance causes concerns with blistering or peeling. The work will be presented at SSPC 2012.
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