by Michael Fallarino


Frankly, as a contractor who often finds himself combing over a building’s exterior for one reason or another, I wouldn’t want to be without a moisture meter.

Decks and finishes
The best example I can offer for the value of my moisture meter is when my work involves a deck or exterior siding. It’s no rarity for pressure-treated (PT) lumber such as ACQ to ship out of yards at 50 per cent moisture content (MC). I know this because I’ve tested PT lumber at 50 per cent MC many times.

Because exterior wood can be damaged by UV in less than one week, it is critical to protect wood as fast as possible. But how fast is too fast? Getting PT wood on to a site before it needs to be installed, and then monitoring it for MC with a meter generates a scientific protocol for deploying a finish properly. In my experience, PT wood will shed its often substantial moisture load much faster than you’d imagine: it can go from 50 per cent to 14 per cent MC in three or four days, even during muggy summertime weather. Likewise, siding and trim, even in a raw, uncoated state, can shed all traces of a substantial rain and return to a baseline of eight per cent MC in a mere four hour stretch of dry, sunny weather. How would you know that without a moisture meter?

No small share of exterior finish problems, are caused by moisture intrusion in a building envelope. If wood or vulnerable building materials are subjected to a MC of 20 per cent or above for a protracted period of time, rot will manifest, and that rot — even in its infancy — can be palpated and detected by an educated hand, without destructive probing. However, what if a section of solid building materials is languishing in a gray zone at 18 per cent MC when it should really be at eight per cent or so? It is in instances like these that a moisture meter can be an invaluable ally.

Meters as marketing
There are other, less tangible benefits to using a moisture meter. Homeowners who have seen me use a meter to test a suspect area of their home and then explain to them the significance of what the meter’s reading means have been appreciative that I go about my investigations in a logical, scientific way.

In cases where the integrity of suspect materials has not been damaged by persistent moisture, it may be impossible to tell if the moisture content of the wood underneath a finished surface is 16 per cent (okay, but high) or 22 per cent (dangerously moisturized). It is for critical interpretations such as these that I feel moisture meters can be — or perhaps I should say should be — an invaluable interpretive aid to clandestine intrusion processes that lurk beneath a surface.

How they work. How they’ve changed
Moisture content expressed as a percentage delineates the weight of water in wood compared to the weight of an oven dry sample of the wood. Because weight is a factor in assessing the measurement as a percentage, manufacturers calibrate their meters using proprietary logarithms that take the specific gravity of different woods into account. Some advanced meters have a user-selectable control so that the meter calibrates its reading to the species of wood being tested.

In the past, most meters used pins (penetrating electrodes). The pins are inserted into the material being tested, and they gather information on the conductance and resistance of the material. Pin-style meters produce accurate, spot-specific readings, but are slightly destructive. Pin style meters are still highly relevant tools. But now we also have pinless meters, which are nondestructive, have the advantage of reading a larger surface area, and the capacity to read further down into the material being tested (3/4” is the nominal depth). They could, therefore, be used to check a plywood substrate beneath some tile, for example. Pinless meters use a small plate and an electromagnetic field to create a reading in a three-dimensional patch of material.

Brand Idiosyncrasies
I had the opportunity to polish my geek antennae by running the seven meters though some rudimentary paces. Interestingly, each manufacturer’s meters were in close agreement with each other. That is, meter readings tended to be extremely congruent within a brand, typically displaying a difference of a tiny fraction of one percent. I hypothesized that the congruency within brands but slightly larger differences across brands reflects the relationships that the manufacturers use to synchronize the logarithmic nature of measuring moisture with the proprietary electronics of their meters. Wager meters tended to read higher than the Delmhorst and Extech in tests on both dry wood and moisture-laden wood, by two to three percent. Among the three brands, Delmhorst and Extech tended to be in basic agreement in rudimentary tests on both dry and moisturized wood, with the Extech meters typically reading a fraction of a percent higher.

All of the meters are battery operated, have an auto-off feature, come with instructions and information on calibrating the readings of the meter across wood species where necessary, and are typically warranteed for one year. Wager meters top out at a measuring capacity of 30 per cent MC while the Delmhorst and Extech reach into the 40 per cent range.

It is important to note that Delmhorst and Wagner are exclusively moisture meter manufacturers. Extech, by comparison, is a manufacturer of scientific meters, as well as thermal cameras and portable printers. They manufacture a vast range of instruments in 15 different categories (such as sound meters where they offer about 20 models). In my opinion, the Delmhorst meters had the most robust build quality and the most expanded range of capacities. Extech’s strengths are their contemporary and ergonomic styling coupled with their value-oriented price point.

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