To help delve a little deeper into the science of drying,here are my
top “Level 2” questions
we get from building
managers, some who, unfortunately, have had to use restoration services more than
How does a moisture meter work?
The science behind why a moisture meter works is rooted in a simple property about H2O. In its liquid state, water conducts electricity. All a moisture meter does is electrify one point of the probe and measure how many electrons pass through the material to the other probe. That relative reading can tell us how much moisture is contained within the building material being measured. One common limitation of a moisture meter is that it will read elevated or “wet” readings on any material that conducts electricity. The mudded-over corner bead in drywall is a common example.
How does thermal imaging work?
Like moisture meters, thermal imaging helps us “see” affected areas of wall due to another property of H2O, but this one is more complicated. Due to its unique properties as an element, H2O has the ability to change from a solid to a liquid to a gas in almost every environment. The water that causes damage in most properties is in a liquid form.
When H2O transitions from a liquid to a gas, it’s called evaporation. The unique property that thermal imaging relies on is the fact that evaporation
actively cools the surface of the material it’s evaporating from. This property allows us to see moisture evaporating through a thermal imaging camera.
Like a moisture meter, one common limitation is a thermal camera tells you temperature on everything, so build-
ing materials that are cooler for other reasons can provide a false positive. An air-conditioning vent blowing on a wall is a common example.
Why is it so hot in here?
The equipment we use generates heat. The common misconception is that the heat generated is intentional. The heat is a byproduct of the electric motors used in our equipment. The heat can actually help us dry because hotter air holds more H2O by volume. Too great of a rise in temperature will start to have a negative impact on how much moisture our dehumidifiers can pull out of the air in a day. An example:
When I was a fresh, excited restoration technician 18 years ago, I followed all of the IICRC specifications for equipment placement on a job. The particular job consisted of a single-story home with no air conditioning.
As the days went by, the temperature kept climbing until on the fifth day of drying it maxed out at 106 degrees and the wood floor I was attempting to dry wasn’t responding to my efforts. Frustrated, I called my supervisor and he advised me to turn off all of the air movers and leave the dehumidifiers running. He said he would come with me in the morning and we would figure something out. The next day we arrived and my wood floor had dried. Over- night, due to a lack of 30 air movers generating heat, the air temperature had dropped below 90 degrees into the maximum efficiency zone of my dehumidifiers. The reduction in moisture in the air created a place for the moisture trapped in the wood floor to go. I would caution everyone that the “turn off the air movers”solution is not universal.
For this reason, we’ll often place our air movers on a low setting in the early days of drying to keep heat generation low and our equipment in the maximum temperature zone.
How do we know what “dry” is?
One step in the drying process is to survey unaffected building materials to determine the EMC (equilibrium moisture content). Since homes sit in a variety of environments, what is a “dry”reading can vary. For example,an air-conditioned home in Ewa Beach may have an EMC of 8 points, whereas a plantation home in Kailua may have an EMC that’s almost double. This is largely a factor of the outdoor environment but can be affected by whether or not the space is regularly conditioned by AC or heat.
Why do some materials dry faster than others?
There are two properties of building materials that can impact the speed with which they dry. Porosity is the first. The higher the level of porosity, the faster the material will dry. Density is second. The lower the level of density, the faster the material will dry. For example, carpet (a highly porous, less dense material)reliably dries quickly where as drywall (a less porous, more dense material) reliably takes more time to dry.
The reality is that drying science is an applied science where we take the theories we think are likely to occur, put them into action and measure the results. Our industry is constantly finding innovative ways for us to address moisture in buildings. I appreciate this community of building managers who have a passion for the science of drying and take the time to ask us the next level questions.
Article by Anthony Nelson, Premier Restoration Hawai'i's Senior Vice President of Operations and Certifications. Anthony is an applied microbial remediation technician, applied structural drying technician, carpet cleaning technician, carpet repair and reinstallation technician, color repair technician, commercial drying specialist, fire and smoke restoration technician, health and safety technician, odor control technician, resilient flooring inspector and water damage restoration technician. Reach him at firstname.lastname@example.org
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