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Checking Moisture w/o a meter question.

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Forum topic by trippcasey posted 488 days ago 553 views 1 time favorited 12 replies Add to Favorites Watch
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trippcasey

72 posts in 521 days


488 days ago

I work in the concrete and aggregate industry, and we frequently check the moisture content of our aggregates before making concrete. What we do is take a sample of the aggregate and weigh the wet sample. Then we dry that sample in an oven or on a hot plate, using a glass lens to see if any moisture is still cooking out of it. When you put the lens over the sample and it fogs up, there is still moisture in the sample. After we are sure the sample has released all moisture, we let it cool and weigh the sample again. Our formula for determining the moisture is

[(Wet Weight – Dry Weight) / Dry Weight] x 100

This works quite well, and is an industry standard.

Could this work with a sample of some of my air drying poplar? It was cut in November, and Im itching to use it. Also, what is a good moisture content to have before using the wood. I have read that 10% + – 2% is good. I was just curious what my ole LJ’s have experience with. Thanks in advance!

-- I almost post pics....until I see the daily top three...then I delete my post.


12 replies so far

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treaterryan

109 posts in 884 days


#1 posted 488 days ago

The Oven Dry Method – That’s industry standard for industrial wood products too. The specs call for a 215 degree oven, dried until the weight stays constant, but a microwave on medium for a few 1 minute bursts work just as well. Just watch you don’t char them and burn some of the weight away.

M=[(W-w)/w] x 100

Where W is the weight of the wood before drying and w is the weight of the wood once fully dried.

12% seems to be most people preference, but I think 15% is just fine. It’s humid in PA anyway and not that many homes have AC. I would think 12-15%MC would work for you in GA, as well.

-- Ryan - Bethel Park, PA

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treaterryan

109 posts in 884 days


#2 posted 488 days ago

Also we Air Dry millions of RR Ties every year, MILLIONS, and this is how we do it. Moisture meters are not that accurate, especially above 25%. Just make sure that dry until the wood sample stops changing weight.

Take an accurate sample too. Not from the end of the board, but a small section at least 1 foot in from the end of a board in the middle of your stack and IMMEDIATELY weigh it, before it has a chance to lose some moisture from the outside of the sample. We use boring bits at work to extract a sample.

-- Ryan - Bethel Park, PA

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trippcasey

72 posts in 521 days


#3 posted 488 days ago

Thats cool, we use 230 for our standard. Anyway, I cooked my poplar today, cut a sample from the middle of an 8/4 peice, and cooked it in the oven at 220 to 215 (had my high low thermometer in their) and ended up with a MC of 15.4%. I think its time to start milling tomorrow. HOOORAAA!!!

-- I almost post pics....until I see the daily top three...then I delete my post.

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treaterryan

109 posts in 884 days


#4 posted 487 days ago

Nice! No reason to drop that money on a moisture meter!

-- Ryan - Bethel Park, PA

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Nomad62

688 posts in 1555 days


#5 posted 484 days ago

Moisture movement is the #1 reason for wood changing shape, it’s not fun to have a project fail due to unsteady wood. I highly recommend getting your wood down to at least 10% mc, then allowing it to set for a couple of weeks to reacclimate to your intended environment. The woods shape will tend to change as it dries, and as it reacclimates; once done the wood will be much more reliable.

-- Power tools put us ahead of the monkeys

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pintodeluxe

3264 posts in 1410 days


#6 posted 484 days ago

When using a DIY dehumidification kiln, I found the amount of water in the DH tank was a reliable indicator of moisture content. Once minimal water was collected in a 24 hr period, the moisture meter also showed equilibrium (no further reduction in M.C.).

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

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trippcasey

72 posts in 521 days


#7 posted 484 days ago

I live in almost a sub-tropical environment down here. Im close to the coast, and our relative humidity fluctuates from 50% to 100%. Different environments work best with different MC from what I read. Just as drying out can change shape, so can soaking in moisture right? Especially when the conditions change rapidly and repeatedly, at least that is what I have read. We can have all four seasons in a week down here, and the humidity changes right along with it, depending on the amount of rain we have had in the last week. My MC has actually increased since I posted this.

Correct me if I am wrong, but couldnt equilibrium be harmful? I know that is when you reach a steadiness that you cant surpass (0.5% + – according to ASTM C567). Then when you take it out of the kiln into a more moist environment, the wood acts like a sponge and begins to absorb the surrounding moisture. I bought some kiln dried wood for my floors when I built my house. The guys begged me to let it acclimate for at least a month before I installed it, and stated that if I didnt the swelling could create problems for me later down the line. I have read here and there that in an environment like I live in, it is better to stick with a moisture content close to what is going to be held naturally over a period of time. I think I will set several pieces of stock of the same size out and monitor them over a period of time to try and get an average of what my natural climate’s “equilibrium” is in the different season. I love experiments. It might be overkill, but fun…and maybe helpful in time.

-- I almost post pics....until I see the daily top three...then I delete my post.

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Nomad62

688 posts in 1555 days


#8 posted 483 days ago

All things considered, that would be the best thing to do. You seem well informed on what you have going on, that is good; you can work around it as well as possible. Using straight grained woods will benefit you, as they change shape less than figured woods; it is the inner tension of the wood that changes its shape, and figured wood have plenty of tension. Resin injection is great, but spendy; products like Pentacryl really help. Best of luck!

-- Power tools put us ahead of the monkeys

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treaterryan

109 posts in 884 days


#9 posted 483 days ago

Wood is always on the move. Even in an arid enviroment. It will move to some degree.

In Waverly, what you have listed in your profile, the average annual humidity is a balmy 85.61%. The average temperature is 67.1F. I have a calculator that solves for equilibrium.

The equilibrium %MC for your area is 18.31, which is one of the highest I have ever seen, they usually fall between 12-15%, except for FL and HI. Obviously in the winter/summer the wood would dry out, while in the wet months, your wood would probably expand to around 20% and contract/expand accordingly.

Your 15+% is probably fine, considering spring’s wet weather is coming and the wood will expand. Generally, wood expands across the grain MUCH more than with the grain (lengthwise).

-- Ryan - Bethel Park, PA

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treaterryan

109 posts in 884 days


#10 posted 483 days ago

Ah, according to the website I was looking at, it looks likes April and May are your dry months and your wet months are mid summer. You guys have some crazy weather there!

-- Ryan - Bethel Park, PA

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trippcasey

72 posts in 521 days


#11 posted 483 days ago

Crazy weather is right. Sunday it was 86F, and this morning I was scraping ice off of my windshield.

How did you figure that EQ? That could be a handy equation to know.

-- I almost post pics....until I see the daily top three...then I delete my post.

View treaterryan's profile

treaterryan

109 posts in 884 days


#12 posted 483 days ago

PM me your email and ill send you a file, its just an excel spreadsheet from a formula out of a text book.

-- Ryan - Bethel Park, PA

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