Refrigerator kiln?

[Richard Coers]

This is so interesting. I have a kiln, but suspect many don’t and use the good old paper bag method as I did for years. I don’t remember any problem with insects using the paper bag method. From my understanding insects need moisture to survive. I think insects need moisture to survive and once the wood is dry they dye. I built my kiln for quicker drying, not really for killing insects. I guess killing insects is a bonus. I do four cycles using my kiln. Start slow 90-100F with a pan of water for 7 days, 100-120F for 7 days, 120-130F for 7 days, and 130-140F for 7 days. I keep it on the last cycle until I have two 3 day reading the same. A little over a month. Now I have no idea if my internal temperature reaches the 133F as described by the USDA. Mostly bowls, but some blanks. However, I don’t expect there are any live insects once my wood is dry in my kiln. Is this a big problem experienced by many that I am not aware of?

I've read that powder post beetle eggs can remain dormant for up to 12 years. The picture is some soft maple I had stored in a shed. Note that there are very few exit holes. So a few exit holes can mean miles of trails. https://blogs.ifas.ufl.edu/volusiaco/2022/08/08/avoid-bringing-home-the-powderpost-beetles-from-yard-and-estate-sales/#:~:text=These pests are active all,be reinfested year after year.

 

[Brian Gustin]

I've read that powder post beetle eggs can remain dormant for up to 12 years. The picture is some soft maple I had stored in a shed. Note that there are very few exit holes. So a few exit holes can mean miles of trails. https://blogs.ifas.ufl.edu/volusiaco/2022/08/08/avoid-bringing-home-the-powderpost-beetles-from-yard-and-estate-sales/#:~:text=These pests are active all,be reinfested year after year.

Yep, and they'll happily much on your grandpappy's 200 year old chestnut secretary desk, if they find some unfinished wood to lay their eggs - they don't care if it's bone dry or not. (they'll also bore into MDF and Plywood - I know from experience.)

 

[DON FRANK]

Richard,
Wood is a good insulator but if you were drying 4" stock in a sawmill kiln you would still have to sterilize. I would think water at 210 degrees surrounding it would do the trick although it might take a bit of time. I might experiment just for the heck of it. Boil a piece of thinker stock for a few hours, pull it out, immediately cut it in half and use a thermal scanner to check internal temp. It would be a good test. Could try several pieces pulled at 1 hr, 2 hr and three hour time periods.

 

[William Rogers]

@Richard Coers Like I said interesting. Removing the moisture moist likely kill the beetles, but the larva eggs will likely survive in a doormat state waiting for the right conditions to re-infest the wood. Then this would be using the paper bag method of drying. Since I do have a kiln, I think my last cycle between 130 and 140 will get the internal temperature to the 133F for at least 30 minutes. This is a 7 day cycle with 6 days added on for a total of 312 hours. I would think everything would be very dead including the larva eggs. I need to rethink if I put my air dried wood in my kiln for the last cycle just to kill any insect and destroy an larva eggs. I haven’t seen any signs of powder post beetles in my stored wood.
@Brian Gustin I would think both of those cases would happen because the right conditions occurred. MDF seems a reach with all the resins and chemicals involved, but I guess anything is possible.
@DON FRANK I have also heard boiling reduces drying time and soaking in DNA works as well. I doubt I would do either for large blanks. For small blanks I have used a microwave.

 

[Mike Novak]

USDA has done the testing on heating times. As an example, they found that it takes between 246 and 304 minutes to raise the core temperature of 6x6 red maple from 60 degrees to 133 degrees in a 157 degree oven at high humidity. That’s under 5 hours. I’m heating for 10 times that long, using the plastic bags to maintain high humidity.

That said, I still plan to track heating time during my next batch. This will be in several weeks because I have a batch of wood drying right now.

Here is a link to the study

https://www.fpl.fs.usda.gov/documnts/fplrp/fpl_rp626.pdf

 

[Mike Novak]

I did my own test on heating time. I drilled a small hole into the middle of a 6” cube that’s been air drying for many years. I put a temperature probe into the hole (tight fit) . Loaded it into kiln with a big batch of dry boards that have some powderpost damage. Set the kiln for 83% humidity and 160degrees. By the time the kiln was up to temperature, the block was above 135deg. This was at 5 hours.

Based on this, and the USDA booklet I’m pretty confident that 24 hours in the kiln at 160 should be plenty of time to kill any critters and spores.

Keep in mind that this test did NOT allow moisture in the wood to evaporate, which would have lengthened the heating time considerably. Equilibrium at 83% 160deg is same as ambient here 70deg 50%, so no evaporation happens. If the wood was wet, I would have wrapped in garbage bags to stop evaporative cooling.

After removing from kiln, I did not see any significant cracks or warping. I think the key is to not allow evaporation.


Since last posting, I have dried a load of white oak bowls and a load of sugar maple. I’m pretty happy with the results. Less cracking than I get just sitting them on a shelf.

For both loads it took 2 weeks at 110/89% to get down to 30%, and then another week raising the temperature each day to finish.

I don’t need the humidifier. If the fridge is closed tightly with the vents taped closed it holds the humidity. It’s going to take me some time to get used to adjusting the vents. A small adjustment makes a big difference.

I added some latches to hold the doors tightly closed. The old seals were not sealing well without it.