{"id":12749,"date":"2021-07-01T18:44:27","date_gmt":"2021-07-01T18:44:27","guid":{"rendered":"https:\/\/insulation.org\/io\/?post_type=articles&p=12749"},"modified":"2021-08-31T18:44:39","modified_gmt":"2021-08-31T18:44:39","slug":"defining-wet-mechanical-insulation","status":"publish","type":"articles","link":"https:\/\/insulation.org\/io\/articles\/defining-wet-mechanical-insulation\/","title":{"rendered":"Defining Wet Mechanical Insulation"},"content":{"rendered":"

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Last month we discussed wet insulation in a metal building industry application. In this article, we address wet insulation in a tightly closed insulation envelope after the system has been in service for an extended period of time.<\/p>\n

Defining \u201cWet\u201d<\/h2>\n

In the mechanical insulation industry, phrases like \u201cremove all wet insulation,\u201d \u201cdo not install wet insulation,\u201d etc. often appear in specifications and guide documents, raising the questions: What is the definition of \u201cwet,\u201d and should all insulation material system components be treated equally when it comes to those types of \u201cwet\u201d phrases? As expected, the answers depend on what definition you look at and whom you ask.<\/p>\n

Merriam-Webster\u2019s online dictionary definition of wet is \u201cconsisting of, containing, covered with, or soaked with liquid (such as water).\u201d Though the general definition is clear, it does not answer the core question of what\u2014from the perspective of the mechanical insulation industry\u2014the definition of wet is. Is any insulation that contains water in any amount considered wet?<\/p>\n

Being a liquid, as described by University of California, Santa Barbara (UCSB) ScienceLine, \u201cwater is not itself wet, but it can make other\u2026 materials wet. Wetness is the ability of a liquid to adhere to the surface of a solid.\u201d1 So, in our industry, when we say something is wet, do we mean a \u201cliquid is\u00a0sticking to the surface of a material?\u201d2 To borrow again from ScienceLine:<\/p>\n

\u201cWhether an object is wet or dry depends on a balance between\u00a0cohesive and adhesive forces. Cohesive forces are attractive forces within the liquid that cause the molecules in the liquid to prefer to stick together. Cohesive forces are also responsible for\u00a0surface tension.\u00a0If the cohesive forces are very strong, then the liquid molecules really like to stay close together and they won’t spread out on the surface of an object very much. On the contrary, adhesive forces are the attractive forces between the liquid and the surface of the material. If the adhesive forces are strong, then the liquid will try and spread out onto the surface as much as possible. So\u00a0how wet a surface is depends on the balance between these two forces.\u00a0If the adhesive forces (liquid-solid) are bigger than the cohesive forces (liquid-liquid), we say the material becomes wet, and the liquid tends to spread out to maximize contact with the surface. On the other hand, if the adhesive forces (liquid-solid) are smaller than the cohesive forces (liquid-liquid), we say the material is dry, and the liquid tends to bead-up into a spherical drop and tries to minimize the contact with the surface.<\/p>\n

Water actually has pretty high cohesive forces due to hydrogen bonding, and so is not as good at wetting surfaces as some liquids such as acetone or alcohols.\u00a0However, water does wet certain surfaces like glass for example.\u00a0Adding detergents can make water better at wetting by lowering the cohesive forces. [Detergents contain saturates that lower the forces in the water and improve wetting.] Water resistant materials\u2026[are] made of material that is\u00a0hydrophobic\u00a0(water repellent) and so the cohesive forces within the water (liquid-liquid) are much stronger than the adhesive force (liquid-solid) and water tends to bead-up on the outside of the material and you stay dry.\u201d<\/p>\n

To some, \u201cwet\u201d usually implies saturation or soaked, but it may suggest a covering of a surface with water or something, as opposed to saturation. \u201cDamp\u201d implies a slight or moderate absorption or some lesser degree of moisture. \u201cMoist\u201d\u00a0applies to what is slightly damp or not felt as dry, and \u201chumid\u201d applies to the presence of much water vapor in the air.<\/p>\n

For most insulation materials, there is an ASTM test to determine the maximum allowable moisture in the material, usually expressed as a percentage by weight or volume. But that does not address the core question of defining \u201cwet\u201d insulation on a project site.
\nWhen you hear talk of corrosion under insulation (CUI) and wet insulation materials, you hear terms like corrosion inhibitor, hydrophobic, hygroscopic, and water resistant. Here is how NIA\u2019s Technical Information Committee defines each of these terms.<\/p>\n