Hardwood Moisture Meters

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General Information 

Professionals within the Hardwood Industry understand the damage created by Moisture and Humidity in-balances on Hardwood Floors. Having a good calibrated Moisture Meter and a Digital Hygrometer are a must.  Hardwood installers, distributors, manufacturers and inspectors know that moisture is wood’s worst enemy.  Wood is a hygroscopic material; i.e. wood absorbs and releases moisture. When humidity increases, or moisture builds up, wood absorbs water and therefore swells and expands causing cupped floors, possible delamination and buckled floors. Dimensional stability is thus affected. Dry environments with not enough moisture (electric heating in winter) will cause gaps between boards and dimensional stability will also be affected.

WOOD Moisture Content or “MC” is the amount of water weight in wood, compared to the amount of dry wood. Both “Pin Moisture Meters” and “Pinless Moisture Meters” measure MC%. Pin Moisture Meters are invasive and leave small pin marks. Pinless Moisture Meters are non-invasive and leave no marks at all. Pin Moisture meters are less expensive but slower to measure a large area. Both Pin and Pinless Moisture Meters need to know what species of wood is being measured.  Once you have chosen a type of meter.  Some meters also come with different displays such as Analog or Digital.  Analog display is a pin moving back and forth infront of a background labelled with percents, they have 3 areas; green, yellow, and red indicating good, okay, and bad levels of moisture content.  Digital displays, display numbers usually from 0-100 which can give you an exact number usually to one decimal place, depending on the meter.   

CONCRETE Moisture Content or “MC” is the amount of water weight in concrete, compared to the amount of dry product. CONCRETE Relative Humidity is another method used to analyze the amount of water vapour in Concrete. Either “Moisture Percentage Moisture Meters (CMEX2)” or “Concrete Relative Humidity Moisture Meters” will provide information on how dry the concrete is. Moisture Meters with Relative Humidity Sensors are invasive and leave holes in concrete. Determining the RH of concrete or Relative Humidity of concrete takes more work but is more accurate. RH sensors are placed into the concrete for 72 hours and are then read. On the other hand Non-invasive Moisture Meters leave no holes at all and are quick and easy to measure large areas of concrete. 

Relative Humidity is defined as the partial pressure of water vapour to the saturated vapour pressure of water at a given temperature, i.e. the amount of water in the air compared to the maximum amount of water that can be held at that temperature. Hygrometers and Psychrometers measure Relative Humidity “RH”. Hygrometers can be purchased at your local hardware store for $4. These are somewhat inaccurate and very slow in response. Professionals use accurate fast acting Psychrometers that can be calibrated if need be precisely to 33% and 75%. Hygrometers and/or Psychrometers both measure “RH”, Relative Humidity. Hardwood floors in Canada should be kept within a relative humidity range of 30-50% RH and at temperatures of 15 to 26˚C. At such levels hardwood floors installed in Canada will fall within an “EMC”, Equilibrium Moisture Content of between 6 to 9% “MC”, Moisture Content measured in %.

Both a pin or pinless moisture meter and a digital psychrometer/hygrometer are mandatory and will help in eliminating problems if used correctly. To eliminate problems, follow some basic rules such as acclimate or equilibrate the wood permitting the wood to become in equilibrium to a new moisture level while at normal ambient conditions where it will be installed for several days. Then measure the moisture of the subfloor and of several pieces of hardwood from various cartons that have been racked. Record your results. The maximum MC difference shall not exceed 4% approximately for strip flooring. If over concrete, measure the Concrete MC or Concrete RH using ASTM rules prior to installing the hardwood.

Calcium Chloride tests are still in use in North America and are a more economical way of testing moisture levels in concrete if you do not do this often

ASTM F2170-11             RH In-situ Concrete Testing (drilling + 72 hr.)

ASTM F1869                  Calcium Chloride Test, Vapour Emission Rate

ASTM 2659                    Non Destructive Concrete Testing “CMEX2”

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