# species combo for the kiln



## greg4269ub (Sep 1, 2009)

I have a question regarding combinations of species in the kiln. I have to dry some walnut for a customer in my next kiln batch however it will not fill my kiln so I would like to top it off with another species. I would like to dry some qsawn red oak along with my customers walnut is that OK or would you guys recommend another species? Thanks for the help in advance.


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## Daren (Oct 14, 2006)

Mixing species is OK in many cases. Some factors to take into consideration are starting moisture content, thickness, species (which you are asking about), the way it was sawn (which you told us)...

Lets say the starting moisture content and thickness are the same. Red oak dries slower than walnut (and white oak dries slower than red oak). 1/4 sawn lumber dries slower than flat sawn. So the walnut is going to be dry first. Walnut is very forgiving air/kiln drying. You will rarely have problems with case hardening or surface check. Oak is bad about surface check if dried too fast.

If the oak is wetter and/or thicker than the walnut I would just run the walnut alone, or find something else to fill the charge.




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## greg4269ub (Sep 1, 2009)

The MC were nearly identical prior to the winter freeze(within a % or 2). I would imagine that they haven't changed much (I haven't checked but I will before I load the kiln) The walnut is both 5/4 and 4/4 and the qsawn R. oak is all 4/4. For some reason my kiln dries the top of the load faster than the bottom (I think this has something to do with heat rising) so given the info that R oak dries slower I will load the oak on top and the walnut on the bottom. 

At what MC difference would you suggest that I not load the oak with the walnut? I do have some walnut of my own to put in there however I do not have a need for any dried walnut at this time so it would kinda over load me on that end but for the sake of having a full load I would put it in there if the can't make the walnut/oak load work.


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## Daren (Oct 14, 2006)

greg4269ub said:


> . For some reason my kiln dries the top of the load faster than the bottom (I think this has something to do with heat rising)
> 
> 
> At what MC difference would you suggest that I not load the oak with the walnut?


Improper air flow...

Not putting an exact number on it, not knowing your set up. But basically wetter oak and dryer walnut is not ideal, even say 5% difference. It's not going to hurt the walnut, just waste space/electric (assuming your kiln is like mine where the RH stay up most of the time until the end of the cycle)

Do a partial load, or throw your walnut in there to top it off is easiest IMO.


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## buroak (Mar 25, 2010)

Try a partial load. I have a sheet of plastic attached to the top of my chamber and wraped around a scrap board on the other end that can rest on the top of the stack and keep the air from passing over the charge of lumber. works real good when the kiln is not full.


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## Allen Tomaszek (Dec 11, 2010)

Hi Greg,

Not sure what the current MC of your stock is but if you're mixing species and the current MC is below 25% for both you could mix even the oak without too much trouble. But as Daren said, if there's too much difference between the oak and walnut you might be better off with plan B.

If it were me I would mix something you have that's already air dried from your yard. I can't remember what you have air drying from the last time I was out by your place but I'd try something other than the oak. If your kiln is drying unevenly and you're unable to fix that then put the air dried stock on the bottom and the walnut on top. 

It sounds a little like Jed Clampett drying technique but I was able to pull it off with a load of 8/4 Cherry and 6/4 Spalted Box Elder crotches with no problem. The Box Elder was air dried and the Cherry was only one week off the saw. Pix of some of the stock below. Probably not recommended in any drying manual but it worked OK for me.


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## Rick C. (Dec 17, 2008)

This is also something I was wondering about.
Thanks for the informative thread


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## jim douglas (Feb 8, 2010)

I recently dried some 4/4 walnut with 8/4 pine. The pine ended up with some discoloration I believe from the black walnut. 
Jim


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## reberly (Jan 9, 2011)

Darn nice looking lumber there Allen,
Rich


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## reberly (Jan 9, 2011)

Hi Greg,
I sometimes mix load my kiln, but I have a solar kiln with some stratification and 2000 cfm of air flow so I use this to my advantage. I put the species with higher moisture content or slower dry time on top and control partial baffles to finish the loads at the same time.
Rich


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## Allen Tomaszek (Dec 11, 2010)

reberly said:


> Darn nice looking lumber there Allen,
> Rich



Darn nice sawyer too Rich.


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## reberly (Jan 9, 2011)

Touchee, 
I have definitely been had.
Rich


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## greg4269ub (Sep 1, 2009)

thank you all for the advice. I tried to load the kiln this past weeknd but it was to cold for the forklift to start i will try again later this week. I did check MC and the oak is dryer by about 5%. I will give the mixed load a whirl and see how it goes. Being that it is all 4/4 and the oak is a bit dryer I think it should work out fine. Guess worst case senario I will be unloading the walnut and keeping the oak in for a bit longer.


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