2 Moisture testers - 2 different readings..sigh

[gensetsteve]

I found the stilhl one about 3 % optimistic. As said above get funny readings normally low batteries then you need to get your battery tester out. I tried the banging together bit I could only sus green and fully seasoned. A meter gives an idea as to how much longer they need to season.

[cornish wood burner]

Check with the meters

Weigh the wood

Dry the wood in the oven or slowly in the microwave

Weigh again

The weight loss is water so that is your percentage of moisture

Weight loss/ original weight is %mc

Some kitchen scales weigh to 1 or 2 grams so ideal and cheap

Edited June 1, 2015 by cornish wood burner

[R5log]

There about £15, not surprised readings are different

[openspaceman]

Take two identical sized samples from a log. You dry sample A completely by measuring its weight occasionally until it stops loosing weight. Say it then weighs 100g and your undried sample B weighs 125 g so B is 20% moisture content.

 

You only need to weigh one piece initially but with a 100gram piece you need accurate scales, I tend to use postal scales and saw a bit that is near enough capacity for the balance.

 

I generally microwave at 25% or defrost setting and check frequently until there is no further weight loss.

 

Green weight - oven dry weight = water content. 100 times water weight divided by green weight give the moisture content in % on a wet weight basis.

 

Leave the piece out of the rain for a few days and you can measure the water uptake it will often absorb 10% of the oven dry weight in summer and more in winter.

 

You can have problems in microwaving large pieces in that the water in the outside layer evaporates, the dry wood on the outside layer then acts as an insulator plus it does not absorb the microwaves as well as water in the inner layers does (bonds have different resonant frequencies) So the water in the middle turns to steam, the steam still trying to get out superheats and reaches pyrolysis temperatures from 250C and up, this splits the wood into char and woodgas but the char spontaneously combusts in the presence of oxygen in the air spaces in the wood. So if you do it too big or too fast the sample starts burning from the inside. First indication with hardwood is a whiff of vinegar.

[Mortimer Firewood]

Stubby

 

Ashes_firewood - I agree, but you are experienced and I'm new to all of this! I'll hopefully learn the right sound, weight and general 6th sense of it all.

 

Kev7937 - Cheers Kev, I'm now full of holes and if I pushed really hard got around 20%

 

Alycidon - Good idea.

 

Woodworks - Whats the oven test exactly? I could take a 25% log and put it in the aga for 24 hours then test both meters again. I suppose that might reveal any faults if the drop is not the same for both.

 

No matter how experienced you get still use the meter some woods give the dry clack but are still wet in the middle. Could be a bit embarrassing rocking up with your seasoned firewood for the client to pick said log out and get a reading of30%

[Woodworks]

No matter how experienced you get still use the meter some woods give the dry clack but are still wet in the middle. Could be a bit embarrassing rocking up with your seasoned firewood for the client to pick said log out and get a reading of30%

 

Have you had customers check the moisture content?

[Mortimer Firewood]

Have you had customers check the moisture content?

 

Yep a few one told me on the phone that he'd like to test them he picked one up and stuck the prongs in the end. After I explained the correct procedure he was really surpprised to find them all sub 19%. Others have tested them after I've left and comented on there dryness on the next delivery. I even ask the customer if they would like me to demonstrate a moister reading most decline.

[Pumpy]

You can have problems in microwaving large pieces in that the water in the outside layer evaporates, the dry wood on the outside layer then acts as an insulator plus it does not absorb the microwaves as well as water in the inner layers does (bonds have different resonant frequencies) So the water in the middle turns to steam, the steam still trying to get out superheats and reaches pyrolysis temperatures from 250C and up, this splits the wood into char and woodgas but the char spontaneously combusts in the presence of oxygen in the air spaces in the wood. So if you do it too big or too fast the sample starts burning from the inside. First indication with hardwood is a whiff of vinegar.

 

It's not just microwaves, this happened to us a few yrs ago, left one in the Esse to dry out, came back a few hrs later after walking the dogs, house full of smoke and a nice bit of charcoal in the oven

[daltontrees]

You only need to weigh one piece initially but with a 100gram piece you need accurate scales, I tend to use postal scales and saw a bit that is near enough capacity for the balance.

 

I generally microwave at 25% or defrost setting and check frequently until there is no further weight loss.

 

Green weight - oven dry weight = water content. 100 times water weight divided by green weight give the moisture content in % on a wet weight basis.

 

Leave the piece out of the rain for a few days and you can measure the water uptake it will often absorb 10% of the oven dry weight in summer and more in winter.

 

You can have problems in microwaving large pieces in that the water in the outside layer evaporates, the dry wood on the outside layer then acts as an insulator plus it does not absorb the microwaves as well as water in the inner layers does (bonds have different resonant frequencies) So the water in the middle turns to steam, the steam still trying to get out superheats and reaches pyrolysis temperatures from 250C and up, this splits the wood into char and woodgas but the char spontaneously combusts in the presence of oxygen in the air spaces in the wood. So if you do it too big or too fast the sample starts burning from the inside. First indication with hardwood is a whiff of vinegar.

 

Fascinating!

 

An alternative is to check a meter on kiln dried wood in nearest buildier's merchants. I used to check mine on any bit iof exposed wood in a centrally heated room. Not a perfect 'absolute' value, but a good relative one.

[njmusk]

Thought I would test mine

 

Stihl EM4806

Ebay special Model MD812

 

Stihl read 2% higher than el cheapo 14-16% in a piece air dried ash