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Author Topic: Drying Urban milled slab lumber  (Read 894 times)

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Offline Classic1

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Drying Urban milled slab lumber
« on: April 14, 2017, 12:04:25 am »
I'm looking for any helpful information on drying schedules or approximate timelines for drying of large slab lumber.  We are located in St. Petersburg, FL so were are in a warm tropical climate, lots of sunshine, relatively high humidity most of the year.  I'd like to build a solar kiln out of a shipping container, but looking for some kind of approximation of drying times so I can figure out how large of a container we'll need, or if perhaps we need multiples. 

We are milling a lot of exotics, camphor, Guanacaste, eucalyptus, podacarpus,rosewood, etc.  But we also get tons of huge oak logs, oaks are the single most common tree down here and we get them massive.  60+" diameter is common.

Currently we've been air drying, it just takes forever.  I've got a load of eucalyptus and camphor in one of those portable carport garages right now to try to speed things up, it seems to be working but I don't have any fans in it to circulate the air. Bottoms aren't tight to the ground so they let in quite a bit of cooler outside air also.  While I could probably make this function better with the addition of some fans and baffling, I'd really like to setup something more permanent. 

Is it feasible to dry 8/4 slabs in 45 days in a solar kiln without dehumidification system, etc?  We have no problems reaching temps of 150 here.   Feasibility of drying mixed loads of lumber? 

Any help appreciated.

 

  

  

 

Offline Ianab

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Re: Drying Urban milled slab lumber
« Reply #1 on: April 14, 2017, 04:54:11 am »
I think 45 days is going to be pushing your luck, especially with stuff like Eucalyptus. You can speed up the drying by upping the heat and airflow, but at some point you start ruining the wood. The solar kilns owe their ease of operation to the cyclic nature of the drying, and the reconditioning that goes on each night. That means that the control doesn't have to be as precise, but you only get 8 or so hours of really effective drying per day. Faster drying needs more precises control of the schedule, more expense, and more energy cost.

But a couple of solar kilns is not a silly idea, given your climate they will be effective all year round, even if the effectiveness varies with the seasons.

You might want to still air dry the more difficult to dry wood for a few months, then move it to the solar kiln for a month to finish it off. I'd think that several modest sized solar kilns would give you more flexibility?
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Offline thecfarm

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Re: Drying Urban milled slab lumber
« Reply #2 on: April 14, 2017, 05:54:09 am »
I just want some pictures of what those slabs are being used for.  ;D
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Offline WDH

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Re: Drying Urban milled slab lumber
« Reply #3 on: April 14, 2017, 07:43:32 am »
45 days to dry 8/4 hardwood slabs in a solar kiln from green?  Can't do it.
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Offline Classic1

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Re: Drying Urban milled slab lumber
« Reply #4 on: April 14, 2017, 07:54:38 am »
Ok, so... if 45days isn't happening.  What would realistic figures be?   I don't have issues air drying before putting into kiln, i'm trying to keep our quality up to get as little degrade as possible.  Our current problem is I have a huge pile of logs on our lot that need to be milled and I need to try to calculate how long its going to take us to process this.  I'd guesstimate we've got 50k bdft+ sitting here and we get more weekly.  I could be getting way more but I've been selective to what we take as we are running out of space.  I'm going to try to cut on our site and probably set the kilns up off site so I have more room.

I know there are kiln manuals and drying schedules, but from what i've seen they pertain to mostly domestic species, and the solar kilns are not in tropical climate areas like we have.


Offline Savannahdan

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Re: Drying Urban milled slab lumber
« Reply #5 on: April 14, 2017, 04:18:12 pm »
Curious, is that a dedicated slabber?  Also, what size can you handle? 
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Offline Classic1

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Re: Drying Urban milled slab lumber
« Reply #6 on: April 14, 2017, 09:23:01 pm »
Yes, it is the dedicated slabber model.  We can handle 76", we've maxed it out on a few occasions.   

Offline GeneWengert-WoodDoc

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Re: Drying Urban milled slab lumber
« Reply #7 on: April 15, 2017, 06:27:20 am »
To maintain quality, I suspect that solar drying time would be no less than 120 days and likely a bit longer.  Drying too fast means cracks and checks--end checks, surface checks and internal,checks.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline Classic1

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Re: Drying Urban milled slab lumber
« Reply #8 on: April 15, 2017, 09:23:00 am »
Is there a definitive guide to drying that includes optimal temperature ranges for % moisture loss per day.  As in 140 degree temperature for 8hrs will equate to xx amount of loss in xxxxx species of lumber?

I saw the chart in the Virgina Tech kiln info pack, but it only gives a reference to max % moisture loss per day.  Because of the different species we use and the fact we are doing slabs, it would be more difficult and wasteful to cut one slab out of every species we're drying to weigh and measure that way as directed.

Also, using the method as described in the VT instructions, there isn't any way for me to plot out the length of time it would be to dry this material as your doing the testing as the wood is drying.  Ideally i'd have a predetermined schedule that would be based on kiln temperature and I'd just need to focus my attention on hitting those target temps as the airflow would be static.

I've got a Tramex moisture meter, it has a chart for the adjusting the values of moisture content read to give true readings based on species from each species specific gravity. 

Seems like I could use that chart as a general reference to extrapolate how different species will dry and at what rates.  Then try to group those species together while drying.

If I had a reference point I'd think it would be easier to figure some of these variable out.

Am I way off base with my thinking?

Offline Den Socling

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Re: Drying Urban milled slab lumber
« Reply #9 on: April 15, 2017, 09:29:36 am »
Too bad you don't have a ton of money. You could dry your slabs in about 2 weeks with a vacuum kiln.

Offline Classic1

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Re: Drying Urban milled slab lumber
« Reply #10 on: April 15, 2017, 11:35:29 am »
Den,  the vac kiln route may be an option.  I'd be interested in hearing more about initial costs, as well as ongoing. I'm sure we could augment our milling operation by outsourcing drying also.  Just have no clue about profitability of this type of work.

Offline Den Socling

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Re: Drying Urban milled slab lumber
« Reply #11 on: April 15, 2017, 12:09:13 pm »
We have customers doing just what you are wanting to do. One new vac kiln is in Los Angeles. Just a few years ago, I never would have thought that we would have a kiln in a city like that!
It's interesting that your saw can handle 76" slabs. Our widest kilns can handle 80".
If you would like an information package, email me at dsocling@vacdry.com.
You're already cutting some beautiful slabs but they are soon going to be stacked up to your ears. They are so big!  :)