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Moisture content

Started by Dewey, August 09, 2017, 05:53:04 PM

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Dewey

Just wondering what is acceptable for moisture content in  air dried Northern White Cedar.... I usually try to get to around 10 %.. I am under the gun to get some Vmatch done its around 12 %
What do you think ?

GeneWengert-WoodDoc

Interior or exterior?  How wide?  The wider the pieces, the more overall shrinkage or movement.  The difference between 10 and 12% MC is pretty darn small...1/2% shrinkage. 
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Dewey

6" interior...  I'm thinking I'm good to go...

Dewey

I've got a new job.... exterior railing to plane 2x6 and 2x2 moisture content is between 12% and 14 %
Can I expect it to plane out ok ????

Ianab

Where I live 12-14% is about as dry as wood gets. It planes fine.
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

GeneWengert-WoodDoc

Interior wood in most of North America is 6% MC in January and 9% MC In summer. Softwoods begin to lose machining quality under 10% MC. So for softwoods, 9.0% to 11.0% MC. Hardwoods are best at 7.0% MC as they shrink and swell more than most softwoods. Ok?
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

RAYGYVER

I've got a question. I am doing hardwood flooring out of Ash. I have a mill. So I am designing the floor boards right now, but I am wondering what MC I should have in Ash to do the final dimensioning and planing? I'm a total newb at wood expansion and contraction. I'm picking up a load of ash logs tonight, they were cut down earlier this year and have been sitting outside in a guys yard, unsealed. Any advice would be appreciated. Thanks

I fear not death, I fear not to live.
Ray Cecil | GrabCAD
www.linkedin.com/in/ray-cecil-b862805b

alan gage

I cut ash this summer/fall to put down for flooring in my house this winter. I cut it 5/8" and will plane it down to 3/8 or 5/16". It will be face nailed with no tongue and groove. Still undecided about width.

To save hauling it back and forth from the house I was going to plane and rip it to width after air drying and then stack and sticker in my heated basement to further dry before install. Just have to hope there isn't any movement in that last couple percent.

I was surprised the other day to see my moisture meter reading 8.5% on the outside (covered) stacks. I didn't think I could expect to get under 11% by air drying but we have been having some nice dry fall weather. I've been meaning to look up the correlation between temp and humidity vs. moisture content to see if that could be accurate.

I'm new at this as well so I'm not advocating you follow my lead.

Alan
Timberking B-16, a few chainsaws from small to large, and a Bobcat 873 Skidloader.

alan gage

Quote from: alan gage on October 25, 2018, 12:16:09 PMI was surprised the other day to see my moisture meter reading 8.5% on the outside (covered) stacks. I didn't think I could expect to get under 11% by air drying but we have been having some nice dry fall weather. I've been meaning to look up the correlation between temp and humidity vs. moisture content to see if that could be accurate.


Well I looked it up and it appears that's probably correct. It also appears I should have taken it off stickers yesterday before the wet humid weather started today. I was really surprised how quickly it dried when cut that thin. Some I cut only 2-3 weeks ago was showing 8.5% yesterday. I assume with this damp weather it will gain just as quickly.
Timberking B-16, a few chainsaws from small to large, and a Bobcat 873 Skidloader.

GeneWengert-WoodDoc

In order to achieve 8.5% MC, the wood must be exposed to and average day and night of 45% RH, which means if the nighttime is around 90% RH, then the afternoon would have to be under 10% RH.  It is rare to see the afternoon as low as the 30% RH range in most of the US.  I think that the reason that the MC is 8.5% is because the pile is covered so you have a mini solar kiln and so the sun heats the air inside the cover.

Almost all homes in the northern half of the U.S. during the winter have a humidity around 30% RH which is close to 6% MC in wood.  Some homes that are fairly tight will have a humidifier and can raise the humidity often to around 40-45% RH or 8% MC in wood.

The issue with floors is that often when installed, the floor is too high in MC, so it will shrink the first year, forming cracks between the boards.  Often these cracks fill with dirt and debris.  If you have 2-1/2" wide ash flooring pieces and they change from 9% MC to 6% MC initially, they will shrink 3/4%, which means a crack between the boards of 0.0075 x 2.5 or about 0.02"...pretty small indeed as that is over 1/64" but it is visible.  The issue becomes more critical if the pieces are wider.  For example 5" wide pieces would have over 1/32" cracks.  The issue is also more critical if the installed MC is higher than 9% MC.

Note that some moisture meters respond more to the surface MC.  However, this wood surface is planed or removed when machining, so the core MC is very important; usually the core is wetter.

Putting the floor together tightly with 6% MC pieces in the wintertime can create a problem in the summer as the pieces swell and will buckle in spots.

Incidentally, i find that the accurate moisture meters will cost over $200.  Would it be worth it to spend this much to avoid moisture issues?

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

RAYGYVER

All very good points. Thank you for the responses. 

Would kerfing the bottom of floor boards before final drying hasten the drying process? Or is that a bad idea altogether? Should final planing and bottom kerfing be done only after desired MC is achieved? 

I am processing 8 acres of Ash logs. I am making Ash flooring for a pole barn, 3,040 square feet of it actually. 640 sq ft is in a loft with 19/32" OSB down. the other 1600 is going down on the main floor. I've got compacted soil, plus 4" gravel, plus 1" leveling sand. I'm not 100% sure on the design yet, but I have the thread WOOD GARAGE FLOOR going in the Timber Framing section. Probably at this point, with all the help from the guys on this forum, looks like 1" foam board plus closely laid sleepers with 1" foam in between those, then face nail the floor boards. Foam with taped seams is the vapor barrier. I have plastic vapor barrier I may lay down in between foam layers.

The only thing I really need from this thread or any MC experts is to help me decide on the thickness and width of these boards, drying time, and if I can get away with square edges or not. The main function other than being a durable floor, is I want to be able to pull up a board anywhere in the floor without removing any other boards. So I am limited to square edge, or shiplap. T&G or Splined edge will not be serviceable one board at a time.  

So in summary I need suggestions:
Sleeper width/thickness
Floor board width/thickness
Drying time/ideal MC
Bottom Kerf before or after drying
Square edge or shiplap?
Anything else I may be missing.
I fear not death, I fear not to live.
Ray Cecil | GrabCAD
www.linkedin.com/in/ray-cecil-b862805b

GeneWengert-WoodDoc

If you use plastic sheet as a vapor barrier, which is a good idea, use only one sheet and one vapor barrier to avoid creating an envelop effect that will trap moisture.

The kerf on the bottom of flooring was developed as a means of removing stress or casehardening.  You will not have stress with proper drying.  Note that all laminate or composite flooring does not have grooves.  Some strip solids floors do not have them.

Is the barn heated to 70 F during the winter all the time?  That will affect the target MC, which affects drying time.  If you air dry first, kiln drying time should be 7 days or less, but it depends on the temperature and kiln equipment.  If the barn is open in the summertime and not air conditioned 24/7, then that affects the target MC.

Before you insulate the floor, consider instead vertical perimeter insulation around the edge extending 24" deep.  With this and because Dry soil is an excellent insulator, you would not need the insulation boards under the floor.  The closer the sleepers, the flatter the floor over time.

The thickness depends on the load and on how many times you will likely refinish the floor.  If the floor will have vehicles, thicker is better indeed.  The width is your option.  As you will face nail, it sounds like ultimate perfection is not required, so I would consider 6".

Square edges are often not used because sometimes a small sliver comes off.  So, the edges are relieved.  This relief also helps hide small gaps.

It is standard practice to machine the product AFTER drying.

I would discourage pieces with straight edges for the joint.  Any cracks between board will go all the way through.  Shiplap is ok and easy to remove one board.  T&G is not that hard to remove one board and replace it.  If you think removal will occur often, consider face screws instead of nails.

Overall, you might find it most helpful to get a wood-flooring installer to spend an hour or two helping with your overall design and installation plans.  His experience will be worth the cost.  We here cannot be confident in our suggestions as we do not know all the details of your application.  So, here we are giving general advice that might still need fine tuning.i
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

RAYGYVER

Gene thank you Sir.

The barn is currently unheated, no ac. Its a steel panel/ laminated wood post building. Felted roof panels to prevent condensation drip "rain" inside barn. I did build a double barrel wood stove for heat, not currently installed. The building has 16' floor to bottom of truss (clear height). So its a large uninsulated barn. The ridge is vented and so are the eaves, so warm moist air in the winter off the stove probably won't build up enough inside the barn to cause it to condense on the walls or ceiling anyway. That is a very large amount of air space to heat with one double barrel stove. It won't get very warm in there. It'll be enough to knock the chill out of the air so I can work. Eventually I will finish the walls in board and batten or shiplap. The walls will still be breathable as to not trap moisture. Maybe I will wrap the walls under the wall panel to help with drafts. I'm just afraid to create that "envelope" inside a wall and it ruins the back side of the steel.

So, being basically outside, the MC of the wood floor will have to correlate to the outdoor RH?? Kentucky gets pretty humid. I'd love to have as wide a board as possible. If 8"-10" is possible, than should I go over 1" thick? I like the idea of bottom kerfing, I can't see how this would hurt at all, only help with the cupping. Yes, I will have a 4 post car lift in one area, and one or two muscle cars sitting around. 
I fear not death, I fear not to live.
Ray Cecil | GrabCAD
www.linkedin.com/in/ray-cecil-b862805b

GeneWengert-WoodDoc

The average humidity in your area is around 13% EMC, summer and winter.  In the barn, with a small amount of heat, you will likely run around 10-11% EMC.  So, that should be your target MC for the lumber.  If you use drier, then you can expect some swelling and buckling.  Cupping is a small risk unless there is liquid water or you have high soil moisture without a moisture barrier.  Unless the kerfs are quite deep, they would not help cupping.  Note that cupping occurs only when there is a moisture change AND the top and bottom have different MCs.  Because of variable grain, wider pieces will move more than narrow.  As a guideline, 12" width moves four times more than 6".
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

RAYGYVER

Gene, 
 Thank you for your expertise. I will take your comments seriously. I am guessing EMC = Environmental Moisture Content? Being new to this, I am not going to understand all the abbreviations right off the bat. Thanks! 8)
I fear not death, I fear not to live.
Ray Cecil | GrabCAD
www.linkedin.com/in/ray-cecil-b862805b

RAYGYVER

Equilibrium Moisture content....okay....googled it
I fear not death, I fear not to live.
Ray Cecil | GrabCAD
www.linkedin.com/in/ray-cecil-b862805b

Don P

This is a good shrinkage calc. Click his link on "wood shrinkage explained" where the text begins;
http://www.woodbin.com/calcs/shrinkulator/
A cheapo thermometer/hygrometer from Walmart or Lowes will give you some starting points.

RAYGYVER

Gene, okay, I spent some time looking over historical RH levels for Louisville KY. We often hit 100%. The most common range of RH is 50-100%, with the average holding somewhere 69% RH. The average high temperature is 68 (f). 

So with this information I can run the calcs...

Worse (wettest) case scenario 100 (f) day @ 100% RH = 27.9% EMC?
Worse (driest) case scenario 0 (f) day @ 33% RH = 6.5 % EMC?
Average scenario 68 (f) day @ 69% RH = 12.9% EMC?

So Gene, I ain't far off from what you told me. How did you arrive at you numbers? Where did you get your data? Is there a nifty calculator tool I missed somewhere?

I fear not death, I fear not to live.
Ray Cecil | GrabCAD
www.linkedin.com/in/ray-cecil-b862805b

RAYGYVER

Quote from: Don P on October 29, 2018, 07:36:47 AM
This is a good shrinkage calc. Click his link on "wood shrinkage explained" where the text begins;
http://www.woodbin.com/calcs/shrinkulator/
A cheapo thermometer/hygrometer from Walmart or Lowes will give you some starting points.
I did a quick calc using your tool for an 8" wide dimension. From 12.9% EMC, to 10% EMC on a 8" dimension, the wood will shrink about 40 thou (.040")
So, if I have a 40' wide barn, and use 8" wide floor boards....thats 60 boards across. .040" x 60 = 2.4" of movement (shrinkage) if the EMC of the floor changes from 12.9% to 10%. Soooooo....if I have 60 boards I have 61 gaps if you include the gaps between the last boards, and the wall. So each gap I will have around .039" allowance for movement for a really dry summer.
So, do I install the floor when the EMC = the average 12.9%? Or should I install the floor when it is slightly higher then 12.9% so that my expansion will never be greater than the day I lay the boards? 
Now, how does the work in the other direction? Along the length of a board? I've got far fewer gaps going that way. Do I need to allow for a 2 1/2" gap at one end of the barn? 
Or is the wood more stable than this? I would assume time is the other factor not included in these calcs. It takes time for the EMC to occur. So are all these calcs just assuming worse case scenario? It is okay to calculate for the average RH and EMC, and assume the EMC will stay within a few points of the average year round?
I fear not death, I fear not to live.
Ray Cecil | GrabCAD
www.linkedin.com/in/ray-cecil-b862805b

GeneWengert-WoodDoc

The outside EMC is in a report
www.woodweb.com/knowledge_base_images/zp/equilibrium_moisture_content.pdf
You will see that the monthly averages for Louisville range from 12.0 to 14.1% with an average of 13.6%.

Wood does not shrink or swell appreciably in length, except fo a rare piece that usually has the pith included.

Your calculations for width shrinkage have the correct process.  Note that there are two values given for wood movement...shrinkage and swelling.  One is for tangential width movement, which is parallel to the growth rings when viewed from the end grain.  The other is radial movement, which is 90 degrees to the rings.  Tangential is twice radial roughly.  However, we rarely have a perfectly tangentially sawn or flatsawn piece, or a perfectly radial or quartersawn piece.  So, especially for wider pieces, we should use a movement number halfway between t and r. For a quarter or rift sawn floor, we might move closer to the radial value.  

The movement values for white ash are 7.8% tangential and 4.9% radial.  So, use 6.3% for your floor.  Divide this number by 30 to get the movement for a 1% MC change, 0.21% / MC%.  So, for your expected movement with a 2.9% MC change, 0.0021 x 2.9 = 0.0061" per inch of width., or 0.61%.  For an 8" wide board, 8x0.0061 = 0.049" or 3/64".  For 60 8"pieces, or a floor 40' wide, 0.0061 x 480" = about 3", but this is spread out between each joint unless you glued the pieces together and then let the floor float, which is common with gym floors.

Note the the so called shrinkage calculations apply to swelling as well.  So, I prefer to call such calculations as wood movement estimates and not shrinkage.

However, when we have a dry piece that is exposed to higher humidity, there is about a 3/4% MC delay or lag before the piece begins to swell.  So, oftentimes swelling calculations are larger than actual. So, we usually prefer a slightly lower MC than the expected average in use MC.  Being wetter than the average can result in shrinkage problems.  Note that this lag also occurs when a dry piece is wetted and then it exposed to dry conditions...that is, it shows up whenever we go from dry to wetter, or wetter to drier.  It is calle hysteresis effect.

Overall, this hysteresis is the main reason why we see issues with wood movement the first year when slightly high MC wood is put into use, but seldom any movement issues in subsequent years.

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

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