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Target MC Reduction/day for Yellow Poplar

10/30/20       
George Barth Member

What is the target daily MC reduction rate when Air drying, Shed drying, or otherwise DH drying Yellow Poplar from Green to 20% MC?

First, I have researched (searched online) and read several of the USDA publications and will specifically reference FPL-GTR-117. Noteworthy, the 117 pub is a bit inconsistent.

Pub 117 References:
P. 2 Table 1 list green yellow-poplar at 83 to 106 MC. Let's use 95% MC for simplicity.
P. 24 Table 7 shows an air drying day range of 1" poplar to 20% MC from 40 days to 150 days...depending on environmental conditions. At the 40 day time, the daily MC reduction rate is less than 2%
P 25, Table 8 has similar times, but adds the 50mm thickness. again 40 days is the lowest time for 1" thickness.

P26, Table 9 it shows cases in Roanoke, VA where the lowest days is 14 or 15. Doing the math: from 95% (green) to 20% or 75%MC loss in 14 days is greater than 5% MC loss per day.

I assume no degrade from the listed references in Pub 117 and only limited by environmental factors (temp / humidity).

So what is the Maximum (conservative) MC loss per day of low temperature (70 degrees F) drying green yellow poplar to 20% without any degrade?

Any data out there or industry standards for Yellow-Poplar for the following thicknesses?

4/4
5/4
8/4
12/4

Thanks in advance,
George

11/7/20       #3: Target MC Reduction/day for Yellow ...
GeneWengert-WoodDoc

I believe you mean FPL- GTR-118.

I do not see the green moisture for yellow poplar in my copy of this text. Incidentally, the headings for this table are reversed.

Appreciate that the average MC loss does not give you the maximum loss rate. In fact, drying to fast at the higher MCs can create damage, even when the weather eases back and drying slows later. The average looks good, but a few days of excessively fast drying can ruin the lumber.

I think by calculating an average rate, you are misusing the original data. Further, the original data was for a specific location.

The maximum daily loss for 4/4 yellow poplar is similar to soft maple.

11/7/20       #4: Target MC Reduction/day for Yellow ...
George Member

Thanks Gene,
I definitely referenced Air Drying of Lumber, FPL-GTR-117 (Seven), October, 1999.

Reference the page numbers and Tables I provided in my original text. Again, I realize the rates are based on the environment, but the Roanoke data (at 5% MC loss in the aggregate) is what interests me.

My 8/4 load now is loosing about 3 to 4 percent MC per day( 50MC to 40MC). Measured in the center from Lignomat PK probes. I pin the outside as well daily and keep a log. I put the pins in about 1/16" and it reads from 15 to 20 MC at various points. So my differential has been about 20 MC from outside to inside.

I am intrigued by the Roanoke 15 day run and wonder if I control the shed conditions (lower the humidity) to achieve those results, will I surface check the Poplar?

I understand that it is way more relisient to high MC derivatives verses Oak. Just wonder what my target should be.

In your class on drying Oak, you give a 3 % MC loss max on 4/4 and I believe half that for 8/4.

what should the target be for Poplar?

Thanks again!
George

11/7/20       #5: Target MC Reduction/day for Yellow ...
GeneWengert-WoodDoc

The Air Drying book you called 117 is a revision of an earlier publication. Many of the photos and tables, plus suggestions are from forty to fifty years ago, so do not represent today's needs and reality very well. The current techniques are not well covered. For example, air drying yards are much more open over the last twenty years or so, so we do get faster drying. In the old days, the yards often had four eight foot wide packs stacked edge to edge, so yards dried more slowly. So, their yard layouts with lots of lumber ina small area are not realistic. Also, yellow poplar when 117 was written was not the premium species that it is now. I

I would rely more on FPL-GTR-118 as two of the authors had practical experience and worked with the industry daily so they saw many practical ideas. They also have appreciated the financial aspects of suggestions.

If you look on page 99, you will find the daily safe drying rate for 4/4 and 8/4 yellow poplar.

Appreciate that weather, air flow, stacking including pile width, and yard layouts are entirely different. For yellow poplar, sheds with fans are great.

11/7/20       #6: Target MC Reduction/day for Yellow ...
George Member

Thanks Gene,
That sheds light on the history and conditions and certainly the evolution of best practices.

I have 118 and and just reviewed that section. Thanks for that tip. That is exactly what I was looking for.

I was hoping to capitalize on knowledge that was out there so I do not turn the Dehumidifiers down too low and damage the loads.

Thanks so much, you are very helpful.

all the best,

George


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