December Newsletter

Even before the sci­ence of wood’s rela­tion­ship with mois­ture was well-under­stood, wood­work­ers had to fac­tor in how mois­ture would affect their mate­ri­als. For­tu­nate­ly, we under­stand well the hygro­scop­ic prop­er­ties of wood today. Thus, we have been able to use that knowl­edge to design wood mois­ture meters that can pro­vide us with quan­tifi­able data about a piece of wood’s mois­ture con­di­tion. As our col­lec­tive under­stand­ing has advanced, the test­ing meth­ods have evolved as well.

Today, there are two main types of hand-held wood mois­ture meters: pin and pin­less. Each relies on dif­fer­ent elec­tri­cal prop­er­ties that are impact­ed by the amount of mois­ture held in the wood being mea­sured, which we will explore in detail lat­er in this arti­cle. For now, it is enough to say that pin-type meters use two nail-like elec­trodes that get insert­ed into the wood and mea­sure the cur­rent that flows between them. Pin­less meters use sen­sor plates that lay flat on the wood’s sur­face and mea­sure the behav­iour of an elec­tric wave they send through the wood.

With­out get­ting into the sci­ence of each mois­ture meter type, the most appar­ent dif­fer­ences between them are what they do to the wood being mea­sured, and how easy they are to use.

Pin meters leave holes in the wood being mea­sured. This makes them use­ful for eval­u­at­ing the mois­ture con­tent of fire­wood or pieces of wood where leav­ing mul­ti­ple holes will not neg­a­tive­ly impact the struc­tur­al integri­ty or aes­thet­ics of the final prod­uct. In con­trast, pin­less meters do not leave any phys­i­cal mark­ers behind. They can only be used on flat wood and the entire plane of the sen­sor needs to main­tain con­tact with the wood dur­ing a read­ing.

A slow pace of work mea­sur­ing wood’s mois­ture con­tent is anoth­er out­come of hav­ing to insert or ham­mer in pins when using a pin meter. Insert­ing the pins to the right depth, remov­ing them, and ensur­ing the pins remain in good con­di­tion to take a read­ing takes time. Con­se­quent­ly, when hav­ing to assess the mois­ture con­di­tion of a large piece or large batch of wood, you have to invest a sig­nif­i­cant amount of time. The more like­ly sce­nario is that you will sim­ply take few­er read­ings. One extends project time­lines and costs, while the oth­er means you will be mak­ing deci­sions with few­er data points guid­ing you. You can work much more effi­cient­ly with pin­less meters since they require less phys­i­cal effort to use and are not as vul­ner­a­ble to phys­i­cal dam­age as the pin elec­trodes.

But this is where we are today. Elec­tric mois­ture meters have near­ly a 100-year his­to­ry. Inter­est­ing­ly, they also still rely on an even old­er method – oven dry­ing – to val­i­date their accu­ra­cy. To appre­ci­ate how hand-held wood mois­ture meters of today oper­ate, it is worth dig­ging into the evo­lu­tion of the tech­nol­o­gy on which they rely.

Researchers first val­i­dat­ed the idea that we could use the elec­tri­cal prop­er­ties of wood as a mea­sure of its mois­ture con­tent in the late 1920s. One of the first portable elec­tric wood mois­ture meters that we find doc­u­men­ta­tion for, is a “blink­er-type” meter, in 1927. This meter had a neon lamp attached to a capac­i­tor, which was in con­tact with the wood. The capac­i­tor would absorb the charge run­ning through the wood. When the capac­i­tor was ful­ly charged, the neon lamp would briefly light up. The faster the capac­i­tor could recharge, the faster the lamp would blink.

How quick­ly the capac­i­tor could recharge was a func­tion of how much resis­tance was in the wood. Since mois­ture con­ducts elec­tric­i­ty, the more mois­ture in the wood, the faster the capac­i­tor would reach a full charge. If there were high resis­tance in the wood (i.e., low mois­ture), then the lamp would blink slow­ly.

With­in the fol­low­ing ten years, a new type of elec­tric mois­ture meter was devel­oped: a vac­u­um tube meter. This meter used a vac­u­um tube volt­meter as part of a Wheat­stone bridge cir­cuit, which uses a resis­tor to mea­sure against the wood being mea­sured. The vac­u­um tube meter is the direct pre­cur­sor to the resis­tance mois­ture meters used today.

By the mid-1940s, pin-type meters were com­mer­cial­ly avail­able. They worked (and still do) by mea­sur­ing the flow of an elec­tric cur­rent between probes insert­ed into the wood. Like the ear­ly blink­er-type meter, the more the cur­rent trav­eled between probes was an indi­ca­tor of low­er mois­ture lev­els. With­out the con­duc­tiv­i­ty of high lev­els of mois­ture, the dry wood pre­sent­ed resis­tance that near­ly elim­i­nat­ed the current’s flow. Some ear­ly pin meters used four probes. Mod­ern pin type mois­ture meters require only two probes.

Dur­ing this peri­od when resis­tance meters were hit­ting the mar­ket, researchers were also explor­ing how dielec­tric prop­er­ties could be used to mea­sure mois­ture in the wood. Dielec­tric mate­ri­als can trans­mit elec­tric cur­rents with­out being con­duc­tors them­selves. This research ulti­mate­ly result­ed in two oth­er types of wood mois­ture test­ing meth­ods that work on two dif­fer­ent dielec­tric prin­ci­ples.

With­out div­ing too deeply into elec­tri­cal engi­neer­ing, these two types of dielec­tric meters used radio waves to mea­sure mois­ture lev­els. The pow­er-loss type of meter looks at how much elec­tro­mag­net­ic ener­gy is lost, which cor­re­lates to mois­ture lev­els. The capac­i­tance mois­ture meter takes the oppo­site approach. It looks at how much elec­tri­cal ener­gy can be stored. What they have in com­mon, on a prac­ti­cal lev­el, is that nei­ther requires pins to break through the wood’s sur­face.

Instead, they use sen­sor plates that emit a radio fre­quen­cy through the wood. The For­est Prod­ucts Lab­o­ra­to­ry (FPL) of the U.S. Depart­ment of Agri­cul­ture had devel­oped a capac­i­tance-type machine to mea­sure wood mois­ture lev­els, but it was not com­mer­cial­ly avail­able. By this time, many man­u­fac­tur­ers were sell­ing pin-style mois­ture meters.

By the ear­ly 1960s, there was one com­mon pow­er-loss type mois­ture meter on the mar­ket. Dur­ing this peri­od, Delmer Wag­n­er, the founder of Wag­n­er Meters, was work­ing as an elec­tri­cian for a sawmill in Ore­gon. The mill used a large, unwieldy vac­u­um-tube in-line mois­ture detec­tor. To build a mois­ture meter that was both small­er and eas­i­er to cal­i­brate, Delmer designed the first-in-line mois­ture meter. This in-line mois­ture mea­sure­ment sys­tem used tran­sis­tors to mea­sure mois­ture. Delmer even­tu­al­ly left the sawmill and, in 1965, found­ed Wag­n­er Elec­tron­ics (known today as Wag­n­er Meters), which built in-line mois­ture meters for the lum­ber indus­try.

Near­ly all hand­held wood mois­ture meters on the mar­ket through the late 1980s were pin mois­ture meters. How­ev­er, these new pin­less mois­ture meters were still quite large, hard to cal­i­brate, and too sen­si­tive to ambi­ent con­di­tions. Con­se­quent­ly, the pin mois­ture meter mar­ket thrived, while there were very few pin­less meters.

In the 1990s, Wag­n­er Meters set out to devel­op a pin­less wood mois­ture meter that resolved the short­com­ings of the pin­less meters then on being sold in the mar­ket­place. Wag­n­er Meters’ first line of hand-held pin­less mois­ture meters had an improved cir­cuit­ry using elec­tro­mag­net­ic waves that result­ed in more accu­rate mois­ture read­ings. Also, the cir­cuit­ry was less sen­si­tive to ambi­ent and wood tem­per­a­ture. Wag­n­er Meters was also able to reduce the size of the hand-held meter sig­nif­i­cant­ly from what was cur­rent­ly avail­able on the mar­ket. Pin­less meters from oth­er man­u­fac­tur­ers gen­er­al­ly weighed at least 10 pounds. The orig­i­nal mois­ture meters were designed for sawmills, but Wag­n­er Meters added one explic­it­ly designed for wood­work­ers by the mid-1990s.

Many experts and ama­teurs alike across the coun­try use mois­ture meters to test the mois­ture con­tent (MC) of var­i­ous mate­ri­als and prod­ucts.

In mois­ture test­ing instruc­tions and “how-to” guides, you may come across the terms “Quan­ti­ta­tive Mois­ture Read­ings” and “Qual­i­ta­tive Mois­ture Read­ings.” What do each of these terms mean, and why would you want to have a quan­ti­ta­tive ver­sus a qual­i­ta­tive mois­ture read­ing?

1. A Quan­ti­ta­tive Mois­ture Read­ing is a rep­re­sen­ta­tion of the mois­ture con­tent of a sam­ple mate­r­i­al which is achieved by using a mois­ture meter that is specif­i­cal­ly cal­i­brat­ed for test­ing mois­ture in that mate­r­i­al. Exam­ples would be the mois­ture read­ings pro­vid­ed by a wood mois­ture meter when test­ing wood, or a dry­wall mois­ture meter when test­ing dry­wall.
2. A Qual­i­ta­tive Mois­ture Read­ing is an esti­mat­ed val­ue using an arbi­trary scale. A good exam­ple of a qual­i­ta­tive mois­ture read­ing would be the results giv­en by a ref­er­ence scale mois­ture meter. The actu­al num­ber is just a rough approx­i­ma­tion of mois­ture con­tent that may not trans­late into a pre­cise mois­ture con­tent per­cent­age.

The dif­fer­ence between quan­ti­ta­tive mois­ture read­ings and qual­i­ta­tive ones can be boiled down to a dif­fer­ence in speci­fici­ty. A quan­ti­ta­tive read­ing is spe­cif­ic and rep­re­sents an absolute mea­sure­ment of mois­ture con­tent in a giv­en mate­r­i­al. A qual­i­ta­tive read­ing is an esti­mate that can be use­ful for comparison—but is ulti­mate­ly not pre­cise enough for many pro­fes­sion­als.

In the restora­tion indus­try, cus­tomers rely on restora­tion experts to elim­i­nate all traces of excess mois­ture in the struc­ture so that it becomes usable again. Whether the prop­er­ty being restored is a res­i­den­tial or com­mer­cial prop­er­ty, lin­ger­ing traces of mois­ture can cre­ate haz­ards such as:

Mould Growth. The growth of black mould and oth­er fun­gi in dark, damp places is not a dan­ger that most peo­ple consider—until they start smelling musty odours and peo­ple with asth­ma and oth­er res­pi­ra­to­ry con­di­tions start to expe­ri­ence side effects of mould spore expo­sure, that is. If too much mois­ture is left in build­ing mate­ri­als fol­low­ing dry-out­/tear-out efforts, then there is a risk of mould grow­ing in the structure—creating res­pi­ra­to­ry health haz­ards.

Poten­tial Struc­tur­al Fail­ures. Excess mois­ture in a struc­ture can weak­en cer­tain build­ing mate­ri­als. For exam­ple, wood beams can rot, mak­ing them sus­cep­ti­ble to break­ing under a heavy load. Water can rust iron-rich met­als, com­pro­mis­ing the per­for­mance of car­pen­try nails and oth­er met­al objects used to keep the struc­ture togeth­er.

Pest Infes­ta­tions. Pock­ets of water hid­den deep in wood­en struc­tur­al beams and in oth­er build­ing mate­ri­als can attract pests such as ter­mites, rodents, and cock­roach­es. These pests can spread dis­ease and eat away at struc­tur­al materials—causing poten­tial harm to the structure’s occu­pants.

The worst pock­ets of mois­ture can usu­al­ly be found using a ref­er­ence mois­ture meter—a qual­i­ta­tive mois­ture read­ing. How­ev­er, when there are mate­ri­als that are only some­what damp, it can be hard to call them one way or the oth­er.

This can lead to the demo­li­tion/tear-out of sal­vage­able mate­ri­als, or less-than-com­plete tear-out efforts as mois­ture-com­pro­mised mate­ri­als are not prop­er­ly iden­ti­fied.

Anoth­er issue in restora­tion work is doc­u­ment­ing the neces­si­ty of dry-out efforts. In many cas­es, the restora­tion pro’s abil­i­ty to col­lect a time­ly pay­ment for their ser­vices depends on the insur­ance company’s will­ing­ness to pay out a prop­er­ty dam­age claim. How­ev­er, before mak­ing any pay­outs, the insur­er will want to ver­i­fy that the restora­tion work was nec­es­sary.

Of course, for a mois­ture meter read­ing to be tru­ly quan­ti­ta­tive instead of qual­i­ta­tive, it is nec­es­sary to ensure the meter’s accu­ra­cy for mois­ture test­ing.

Ensur­ing mois­ture meter accu­ra­cy has sev­er­al com­po­nents, includ­ing:

Choos­ing the Right Mois­ture Meter. To get quan­ti­ta­tive mois­ture mea­sure­ments, the mois­ture meter needs to be prop­er­ly cal­i­brat­ed for the mate­r­i­al it is being used on—a hay mois­ture meter will not pro­duce accu­rate results in wood, and vice ver­sa.

Main­tain­ing the Mois­ture Meter. Main­te­nance plays a sig­nif­i­cant role in ensur­ing mois­ture meter accu­ra­cy. A meter with dam­aged pins/scanning plates, deplet­ed bat­ter­ies, and a degrad­ed cir­cuit board is not going to work at peak accu­ra­cy and effi­cien­cy. Tak­ing care of your meter is crit­i­cal for get­ting quan­ti­ta­tive mois­ture mea­sure­ments.

Check­ing the Meter’s Accu­ra­cy. Even a well-main­tained mois­ture meter can lose cal­i­bra­tion after years of use. So, peri­od­i­cal­ly check­ing the mois­ture meter’s cal­i­bra­tion using a mois­ture con­tent stan­dard (MCS) or built-in cal­i­bra­tion check can be invalu­able for ver­i­fy­ing that the meter is pro­vid­ing accu­rate mea­sure­ments.

The term “ref­er­ence scale” is used for a mois­ture meter read­ing mode where­in the meter takes qual­i­ta­tive mois­ture read­ings as opposed to quan­ti­ta­tive ones. These qual­i­ta­tive mois­ture read­ings are shown as a numer­i­cal val­ue which the user can then use to esti­mate whether that mate­r­i­al is “wet” or “dry.”

It is impor­tant to note that the num­bers used in a ref­er­ence scale are not indica­tive of a spe­cif­ic per­cent­age of mois­ture con­tent. Instead, mea­sure­ments in the ref­er­ence scale are used as a rel­a­tive indi­ca­tion of how much mois­ture a mate­r­i­al has in it.

For exam­ple, say you have two dif­fer­ent mois­ture meters. One meter might have a ref­er­ence mode set­ting that dis­plays mois­ture val­ues from 0–300, while the oth­er one goes from 0–100. While it might be tempt­ing to think of read­ings on the 0–100 ref­er­ence scale meter as per­cent val­ues, they are not. A read­ing of 12 on a 0–100 scale does not mean that the mate­r­i­al has 12% MC; it just indi­cates that the mois­ture con­tent is rel­a­tive­ly low.

The pri­ma­ry use of the ref­er­ence scale set­ting on a mois­ture meter is to give it util­i­ty beyond read­ing mois­ture in one kind of mate­r­i­al. Using a ref­er­ence mois­ture meter read­ing mode, you can get a gen­er­al idea of the mois­ture con­tent of many dif­fer­ent mate­ri­als that do not have a spe­cif­ic read­ing scale.

One of the best ways to use a ref­er­ence scale meter is to take a read­ing from an unaf­fect­ed, dry sam­ple of mate­r­i­al. Once you have a read­ing from the “dry” sam­ple, you can use that data as the base­line for the ref­er­ence scale read­ings you get for that mate­r­i­al for the rest of the job.

For exam­ple, if your dry mate­r­i­al (car­pet, for exam­ple) reads 33 on a 0–100 scale, and anoth­er sam­ple of the same type of mate­r­i­al reads 56, then that sec­ond piece of mate­r­i­al is at least slight­ly damp.

This process of sam­pling a dry mate­r­i­al to com­pare the dry read­ing to oth­er read­ings of the same mate­r­i­al should be done for each mate­r­i­al being test­ed, each time you are at a new job site. Also, if you are test­ing for mois­ture in both inte­ri­or and exte­ri­or envi­ron­ments, take ref­er­ence read­ings for mate­ri­als in both areas. The rea­son for this is that dif­fer­ent mate­ri­als might reach their equi­lib­ri­um mois­ture con­tent at dif­fer­ent lev­els depend­ing on the humid­i­ty of the envi­ron­ment. The humid­i­ty may change slight­ly from one job site to the next, and more so from the inte­ri­or to exte­ri­or envi­ron­ments.

Addi­tion­al­ly, for restora­tion work, you may want to per­form the ref­er­ence read­ing dai­ly, as the ambi­ent humid­i­ty of a struc­ture will change as dry out efforts progress.

Anoth­er way to use the ref­er­ence scale is as a quick “wet or dry” indi­ca­tor for mate­ri­als. On some ana­log ref­er­ence mode mois­ture meters, the dis­play has a colour-cod­ed indi­ca­tor. For exam­ple;

Green. This colour indi­cates rel­a­tive­ly low mois­ture.

Yel­low. This colour indi­cates some mois­ture — enough that mate­r­i­al may be at risk and needs to be test­ed with a ded­i­cat­ed meter or some oth­er accu­rate method.

Red. This colour indi­cates very high mois­ture con­tent — the item is water­logged.

Although these are qual­i­ta­tive mois­ture read­ings rather than quan­ti­ta­tive ones, when a meter response is extreme­ly high, that is a good indi­ca­tion the mate­r­i­al is mois­ture-com­pro­mised.

While most DIY projects prob­a­bly will not require rel­a­tive humid­i­ty (RH) test­ing, there may be occa­sions where know­ing the ambi­ent humid­i­ty con­di­tions can be use­ful.

For exam­ple, you may want to per­form rel­a­tive humid­i­ty test­ing in your house after a water dam­age reme­di­a­tion com­pa­ny declares that they have com­plet­ed their dry-out oper­a­tions. High ambi­ent humid­i­ty in a room could be an indi­ca­tion that there are still mois­ture-com­pro­mised mate­ri­als in the area, and that dry-out oper­a­tions are not com­plete.

There are oth­er exam­ples of times that you might want to use a ther­mo-hygrom­e­ter—also known as an RH meter—such as when you’re prepar­ing to install hard­wood floor­ing, check­ing your heat­ing, ven­ti­la­tion, and air con­di­tion­ing (HVAC) sys­tem, or when assess­ing mould risk in a base­ment. What­ev­er task you end up using your RH meter for, how­ev­er, you prob­a­bly want to make sure that the rel­a­tive humid­i­ty read­ings you get are as accu­rate as pos­si­ble.

Ensur­ing RH meter accu­ra­cy can be dif­fi­cult, as rel­a­tive humid­i­ty read­ings can be affect­ed by sev­er­al dif­fer­ent fac­tors, such as:

1. The place­ment of the sen­sor.
2. Con­t­a­m­i­nants on the sen­sor ele­ment.
3. The tem­per­a­ture of the room being test­ed.

The first issue is eas­i­ly con­trolled, and dif­fer­ent RH meters will usu­al­ly have place­ment tips includ­ed in the owner’s man­u­al to help you avoid prob­lems.

The sec­ond issue is one of main­te­nance and stor­age. To pre­vent this issue, avoid keep­ing your thermo-hygrometer’s sen­sor out when it is not in use, stor­ing it in its case when­ev­er pos­si­ble. If an RH sen­sor does get too bad­ly con­t­a­m­i­nat­ed, you will need to replace it.

How­ev­er, the third issue, the ambi­ent tem­per­a­ture, is one that many DIY enthu­si­asts might miss when check­ing the accu­ra­cy of an RH meter.

Ter­mi­nol­o­gy

Mois­ture Zones (MZ)

• Indi­cat­ed by led lights – Green, yel­low, red
• Mois­ture zones the meter will see

Wood Mois­ture Equiv­a­lent (WME)

• Meters are cal­i­brat­ed to wood
• Not mois­ture con­tent, mois­ture equiv­a­lent
• Wood is a con­sis­tent prod­uct
• Even elec­tri­cal con­nec­tiv­i­ty between species
• Hygro­scop­ic mate­r­i­al

What wood would obtain if left in the prox­im­i­ty of anoth­er mate­r­i­al;

i.e.

If you had con­crete read­ing 25%wme and you sat wood on top of that con­crete.  If the wood was read­ing 14%wme, then the mois­ture from the con­crete will move into the tim­ber and if left in that envi­ron­ment, the tim­ber will decay.

Mois­ture moves from wet to dry to try to equal­ize and find equi­lib­ri­um.

Pin Meter Read­ings (PMR)

• Mea­sures the resis­tance between two pins
• Very repeat­able
• Addi­tion­al exten­sions avail­able

Non-Inva­sive Read­ings (NIR)

• Aver­age read­ing across ¾ inch (20mm) depth
• Or high­est read­ing depend­ing on the meter
• The con­duc­tance of the mate­r­i­al / Rel­a­tive fre­quen­cy method (RF)

Rel­a­tive Humid­i­ty (RH)

• Meters do not read below 7%

Infrared ther­mome­ter (IR)

• Cal­cu­lates the dif­fer­ence between dew point and sur­face tem­per­a­ture

Ther­mal Imag­ing (Ther­mog­ra­phy)

• An addi­tion­al tool which shows the dif­fer­ence in tem­per­a­ture by colour

Picked by Phill McGurk

1. Jon Jones                              @Jonnybones
2. Khabib Nur­magome­dov      @TeamKhabib
3. Aman­da Nunas                    @Amanda_Leoa
4. Stipe Mio­cic                          @stipemiocic
5. Kamaru Usman                    @USMAN84kg
6. Valenti­na Shevchenko       @BulletValentina
7. Israel Ade­sanya                   @stylebender
8. Weili Zhang                          zhang­weil­im­ma (Insta­gram)
9. Petr Yan                                @PetrYanUFC
10. Alexan­der Volka­novs­ki       @alexvolkanovski

*Pho­to Cred­it @UFC

Released this month

• Stan­dard Oper­at­ing Pro­ce­dures Tem­plate
• Hir­ing Process
• Onboard­ing Process
• SOP for the Tramex ME5 Mois­ture Meter
• Mar­ket­ing Video for the Asth­ma and Aller­gy Product/Service to use in your busi­ness
• How to apply for a police check?
• How to apply for a blue card?
• How to apply for a white card?

Com­ing up next month

• How to com­plete a JSEA
• How to com­plete SWMS
• Train­ing Reg­is­ter Check­list
• Intro­duc­tion to ATP Meters
• How to opti­mise your Face­book Busi­ness Page
• Train­ing Process
• How to com­plete a Stan­dard Oper­at­ing Pro­ce­dure
• Intro­duc­tion to Mois­ture Meters — Train­ing Video