Wood Moisture

[Doug Jones]

I recently bought some hackberry wood (hard dense wood with open pores, a lot simular to oak in its characturistics but not looks) the moisture was 13%. I am without a moisture meter myself and was curious if anyone can give me an idea how long would it take the wood to get down to 7-8%?
Its stickered in the garage, we are in the 80-90 degree range with about 70% humitity. I have the fan running on medium at an angle down the lenght of the wood. This question might be a long shot to get a answer but I had to try.
TIA, Doug

[Glenn Clabo]

I recently bought some hackberry wood (hard dense wood with open pores, a lot simular to oak in its characturistics but not looks) the moisture was 13%. I am without a moisture meter myself and was curious if anyone can give me an idea how long would it take the wood to get down to 7-8%?
Its stickered in the garage, we are in the 80-90 degree range with about 70% humitity. I have the fan running on medium at an angle down the lenght of the wood. This question might be a long shot to get a answer but I had to try.
TIA, Doug

Great question...made me use the gray matter. Most of the time I just wait for it to settle down to where it's stored...which is in my shop...which is pretty close to where it's going.

Outdoor relative humidity actually changes little from season to season (on average) so I'd say it's not going to change a whole lot. The moisture content of wood used or stored outside (ie: your garage), but protected from direct wetting (assuming you have a roof :D), varies little through the seasons...on average. It's inside homes where the relative humidity of the air drawn inside is changed by heating it and cooling it without humidification or dehumidification, that wide seasonal swings in relative humidity, and hence, wood moisture content and dimensions, will be noticed.

Installing a humidifier/dehumidifier to control relative humidity indoors, is the best way to minimize changes in wood moisture content and dimensions...which will allow you to build with wood conditioned to the average moisture content (equalized) that it will see in service. Which means...built it to as close as you can where you want it to be. Do you really NEED it to be 7%? Kindah low IMHO...but where will it end up is the question that needs to be answered.

But...maybe my gray matter is getting tired after all.:)

[Todd Burch]

Your wood will only reach 7%-8% moisture content (or more properly termed as "EMC", or equilibrium moisture content) when the surrounding temperature and relative humidity will allow it.

See the chart here:

EMC Chart (http://www.csgnetwork.com/emctablecalc.html)

With your current temp/humidity level, it will never reach that low. This fall or winter, when you humidity and/or temperature drops, then your wood moisture content will drop with it.

A quick ratio chart is @ woodweb here:

EMC / Relative Humidity Chart (http://www.woodweb.com/knowledge_base/EMCRH_ratios.html)

So, your RH needs to be between 32% and 46% before your wood will be in the 7% to 8% range.

I used to know where an EMC map for the USA was (I think Virginia Tech...) but I couldn't find it. It would show you what the EMC is for your locale.

[Doug Jones]

Your wood will only reach 7%-8% moisture content (or more properly termed as "EMC", or equilibrium moisture content) when the surrounding temperature and relative humidity will allow it.

See the chart here:

EMC Chart (http://www.csgnetwork.com/emctablecalc.html)


A quick ratio chart is @ woodweb here:

EMC / Relative Humidity Chart (http://www.woodweb.com/knowledge_base/EMCRH_ratios.html)



Great links Todd, Thanks, these will help for future questions.

[Gord Graff]

Hello Doug,

I can't add a whole lot to what the others have said, well said it was and the links were great. But I can tell you from personal experience that the money I spent on the moisture meter below was money well spent. I don't guess any more at the material's moisture content and I believe that my work has improved because of it. It's a tool that not many of us think about but one that has proved itself invaluable to me and many others. I hope this helps.

All the best
Gord

[Glenn Clabo]

I used to know where an EMC map for the USA was (I think Virginia Tech...) but I couldn't find it. It would show you what the EMC is for your locale.

Hey Todd...great links. It caused me to look further so I found thius link...
EMC of WOod in Outdoor Locations in the US and Worldwide
http://www.fpl.fs.fed.us/documnts/FPLRN/fplrn268.pdf

[Todd Burch]

Glenn, that's a great reference too. Thanks.

The chart I was looking for was a graphical chart, kinda of like a topography map, showing the EMC in different domestic regions. But, a table will work too! (It looks like Houston is rated a bit high though - in the 14's all the way across. I think it's more like high 12's, low 13's - but what do I know....)