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Author Topic: Drying 8/4 Hard Maple  (Read 851 times)

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Offline PA_Walnut

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Drying 8/4 Hard Maple
« on: January 25, 2018, 06:26:44 AM »
I just sawed a BEAUTIFUL (think "perfect") big hard maple log. Was able to get 8/4 that is about as close to flawless as it gets.

Frozen log, requiring carbide AND slow, and then immediately got it on fluted sticks, but am aware of the daunting tasks of drying it properly, doing the dance between stain and checking. Also, can't get it in the kiln for at last 2 months.

An advantage is that it's cold here again. It's mostly in the mid to upper 30's with a few days reaching 50° or so. Should I still dry to get some fans on it to get the surface dried? Shade the stack sides?

THanks.
I own my own small piece of the world on an 8 acre plot on the side of a mountain with walnut, hickory, ash and spruce.
LT40HD Wide 35HP Diesel
Baker Portable Edger with Kubota Diesel
Kubota M62 Tractor/Backhoe
WoodMizer KD250 Kiln

Offline GeneWengert-WoodDoc

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Re: Drying 8/4 Hard Maple
« Reply #1 on: January 25, 2018, 07:13:42 AM »
Keep the rain off of it...100%.

The discoloration Is most active above 50 F.  Fans, in air drying, run when the humidity is under 85% RH and temperatures are over 50 F, would be an excellent idea.

Anything you can do to minimize air drying and get this into the kiln at around 75% RH and 100 F is really a great idea.  Otherwise, you can find that the outside of the lumber, when you finish drying, will have a grey ring with the inside being whiter.  That is, partial air drying and then kiln drying can create bi-colored wood, outside to inside.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline PA_Walnut

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Re: Drying 8/4 Hard Maple
« Reply #2 on: June 03, 2018, 06:41:35 AM »
It's always the maple...

Put some high-grade curly on sticks (fluted, breeze-dried sticks) and within a week,  with the humid and rainy weather we're having constantly, noted the very early signs of staining, even with fans.  (can't get the surface dried fast enough).

Got it into the kiln right away at 105° and full venting to try to dry the surface. Eeked it up to 110° after 1st day, trying to preserve snowy white color.

Working on 5%/day MC loss. 

Gene (or others), you like this plan so far? I will baby-sit this load 24/7 if I need to. It's EXCELLENT stock that must not suffer degrade.
I own my own small piece of the world on an 8 acre plot on the side of a mountain with walnut, hickory, ash and spruce.
LT40HD Wide 35HP Diesel
Baker Portable Edger with Kubota Diesel
Kubota M62 Tractor/Backhoe
WoodMizer KD250 Kiln

Offline GeneWengert-WoodDoc

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Re: Drying 8/4 Hard Maple
« Reply #3 on: June 03, 2018, 07:30:44 AM »
You understand that color is determined mainly by the speed of drying when the lumber is above 40% MC average.  Also, low humidity is critical for good color.  We want at least a 8 F wet-bulb depression, which is 77% RH or 14% EMC.  For 4/4 - 6/4, a 10 F depression or 70% RH and 12% EMC is appropriate.  We also know that 100 F dry-bulb will be whiter than 110 F.

Let’s assume that the outside humidity is 100% RH in the early morning and the temperature is 70 F.  If we had an empty kiln and heated this air to 100 F, the humidity would drop to 30% RH or 6% EMC. Now, if we had a small amount of lumber in the kiln, as the lumber dried, the RH in the kiln would increase.  Our controls would then exhaust this humid air rather quickly and bring in outside air that would be heated and create 30% RH, even at noon or even in the afternoon.  So, at 100 F, the venting process will allow us the generate very dry conditions in the kiln.  Two things are required...a good venting system that can exhaust the moisture from the lumber (large enough vents and good power from the fans to make the vents work) and a good heating system that can heat all the incoming air to 100F.  Unfortunately, in many kilns, as we put more and more lumber into the kiln, the vents are not large enough and/or the circulating fans that make the vents work are too small or run too slowly.  That is, they can no longer vent fast enough.  In fact, in some kilns, we need to crack open the main doors to get enough venting.  With the high venting comes a very large demand for heat.  (Operations with a DH kiln have the same issue...the compressor is unable to remove moisture from the kiln air fast enough.). To be clear, at 100 F, a standard kiln can operate with 8/4 maple and get 77% RH or lower from outside air if the vents are large enough, fans are large enough, and heating is large enough.

Here is the bad news...many kilns are designed for oak and do not have adequate venting.  So, this means that in the summer, a kiln cannot be fully loaded with maple or white pine or poplar, etc.  The amount of lumber must be reduced to 2/3 of the "normal" capacity.  With less lumber and less evaporated moisture, the vents work better and the RH is under control.  You could also increase the dry-bulb temperature, and then the vents would be more effective, but this extra heat does affect color.

Some people with several kilns will load two kilns half full for three days, dry quickly and establish good color.  Then they put the two "half" loads together and dry normally, as the drying rate does indeed slow down after a few days, so the vents work better.  Another option is to load a kiln 2/3 full for a few days achieving the correct RH and 100 F.  Then load the remaining 1/3, with the fans blowing through the drier lumber and then the wetter lumber for the next two days...overall, not the best plan, but better than a full kiln right from the start.

Note that if we air dry for a few days or a week before going into the kiln, we have a high risk of getting maple with two colors...the shell is one color from the high outside RH and cool temperatures and the core is a different color from the 100 F temperature that exists 24/7 and consistently low RH.

Questions?
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline YellowHammer

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Re: Drying 8/4 Hard Maple
« Reply #4 on: June 03, 2018, 08:15:03 AM »
Yes, put fans on it.  I use two big barrel fans, on high, which put side by side cover 8 feet of stack, four feet high.  The more wind you put on it, the cooler it will stay due to evaporative cooling, and the better the color will be. Watch for checks.  

Yes, get it in a shady place immediately.

Once the MC drops out of the higher ranges, it will be ok, if you can get it down fast enough.  







  
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Offline PA_Walnut

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Re: Drying 8/4 Hard Maple
« Reply #5 on: June 03, 2018, 09:19:29 AM »
Thanks for the tips...I ALWAYS get maple in the shade and on sticks within hours at most. The sticks are also fluted Air-o-flow sticks so that I don't have sticker-stain to contend with also. 

Only lost about 2-3% since yesterday, so need to get more venting. (now venting 100%). Trying to bump up the heat a little to increase depression. Maybe crack the door also.
I own my own small piece of the world on an 8 acre plot on the side of a mountain with walnut, hickory, ash and spruce.
LT40HD Wide 35HP Diesel
Baker Portable Edger with Kubota Diesel
Kubota M62 Tractor/Backhoe
WoodMizer KD250 Kiln


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