Insulation Failure Due to Moisture
This study,Temperature and Moisture Dependence of the Thermal Conductivity of Insulation Materials, covers conductive insulation materials ranging from rock wool to foam glass to perlite, at temperatures from 0 C to 80 C.
Our point is not that ceramic coating are necessarily superior to conventional insulation materials. The point is that ceramic-based coating does not degrade due to moisture content and conventional conductive material fails dramatically with even small levels of moisture. Ceramic coating also eliminates corrosion under insulation (CUI) while wet insulation is the direct cause of CUI.
The study’s summary states: “Insulation materials are exposed to environmental influences (i.e. rain or humidity). Due to diffusion processes as a consequence of gradients of the temperature or the humidity, the moisture content of the insulation can increase. High temperatures at high moisture contents lead to a strong increase of the effective thermal conductivity because of pore diffusion.” In other words, conventional insulation materials conduct more heat when wet. In the chart below, derived from figures in the study’s “Figure #4, conductive loss causes rock wool to yield a thermal conductivity at or close to the same k values as wood fiber board, plaster wood lathe, and not far from water or window glass at 140F and 176F temperatures. I added the other materials’ k values to provide a comparison to rock wool’s wet insulation k value.
|
Material |
k value @50 F+ 0 % humidity |
k value @68 F+ 19.5% humidity |
k value @104 F + 19.5% humidity |
k value @140 F + 19.5% humidity |
k value @176 F + 19.5% humidity |
|
Rock Wool |
0.04 |
0.2 |
0.3 |
0.5 |
0.85 |
|
Comparable Materials and Their k Values |
Rock Wool’s dry rated value |
Wood Fiber Board |
Plaster, Wood Lathe |
Water = 0.58 |
Window Glass = 0.96 |