project: bake the bugs!


Bill Tarbell

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All of the wood i've purchased so far has been air dried outdoors.  I didn't think much about possible infestations when i bought it, but i recently had a bug scare so i figured it'd be best to sterilize the wood.  After researching for a bit I came up with a plan on how to heat up a chamber to 150F.  Once it reaches that temp it should be held there for a few hours to ensure the wood is heated throughout.  The internet indicates that the internal temp must reach 130F for at least 30 minutes.

 

I built the chamber out of 3 full sheets of 1" insulation board. I already owned enough to cover the end caps, so if you build one of your own you'll need 4 sheets.  The chamber is roughly 12L x 4W x 2H.  I debated a while on if i'd need wooden supports inside, but decided it was unnecessary.  I sealed the joints with duct tape and then tossed some harbor freight blankets over them as well.. being careful not to cover up the wiring, just in case.

 

The heat is generated by an electric fireplace insert replacement.  It was only 30$ on amazon and it includes a blower fan.  This was the cheapest heating solution i could find (space heaters have a safety switch that turns them off at around 100F).  I wired up the fan to always run and connected the heater element to a temperature controller module.  The module was $18 on amazon.  It has a thermo sensor on a 6' wire and will turn allow you to set a specific temp to maintain.  You can specify the spread separately from the temp.. i chose 150F as the temp and 10F as the spread.. so it'll turn off at 160F and turn back on at 140F.  (note: the model i linked only reads in Celsius.  They make a fahrenheit model, but, ironically, it is labeled in a foreign language.  I goofed up when using the F model and wired it improperly at first (power into the thermo ports). It didn't smoke, but when i corrected the wiring it failed ot turn on, so i guess i killed it. I then bought the C model as a replacement).

 

Here's the wiring diagram in case someone wants to make it the same way i did:

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And here's the size of the stack.  Sadly, it'll take me about 6 or so batches in order to sterilize all the wood i've acquired.

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Here's what the finished chamber looks like.  The heater is positioned about 8 inches or so away from the foam and is blowing toward the wood stack.  The thermo sensor is inserted at the far other end of the chamber near the floor.  I also inserted a cooking thermometer at that side as a way to double-check the temp.

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Yeahhhh.....but.....sterilize the boards and miss a few bugs on the floor under the thing.....in 3 months you have a new crop.  

Definitely a worthy concern.  Thus far, the only bugs i've found in the shop so far have been identified as booklice, which are thankfully benign.  This is more of a precautionary step in case there are eggs inside waiting to spring bugs i've yet to see.  

 

I didn't craft a base for the chamber, so it's actually just 4 walls sitting directly on the concrete floor.  Bugs could easily crawl out under the walls, but if they stayed in the chamber they'd die from the heat.  

 

 

Pretty ingenious ! I would have several smoke detectors handy just in case. Garden hose and fire extinguishers also on hand.

I've been going down every 15-20 minutes to check on it.  I can't detect any leaks, but it's heating up a bit slower than i imagined it would.  After about 1.5h it's up to around 100F (air is about 70F).  I currently just have a little fire extinguisher, but bringing the hose around is a solid idea.

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I seriously considered that when i first discovered the bugs.  My main concern with using a pesticide was for our health as well as the health of our cats.  The pesticides i found that are benign to humans all seemed to be toxic to cats. The cats never go down into the basement, but one could certainly slip through the door as i'm heading down, so it was still a concern.  Boric acid is benign to both humans and cats, but it only works on insects if they eat it, so it's not quite as effective as typical pesticides.

 

Here's a closeup of the bugs i found in the shop.  I only found around 15-20 over a couple week span and they were all extremely small, about 1mm or less in length.

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And here are some google images for booklice.  I'm pretty confident that they're what i was seeing.

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Booklice only eat microscopic mold/mildew on the wood and do not damage the wood itself.  If i found any other bugs then i'd be much more concerned and would likely at least try the boric acid.  As of now, it's hard to justify using any chemical pesticides in the house.

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I would drill a hole deep into the edge of a board in the middle of the stack and use one of those digital kitchen thermometers with the probe on a armored lead you can put in the oven. Mine has an alarm that goes off when the roast reaches the temperature you set.

You could drill the hole near a flaw that's going to get cut out anyways.

Alarm goes off and you start a timer to give it the 30 - 45 minutes it needs to kill the pests.

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You could spray behind and under things where you don't go and the cats can't get to.  I'm thinking for each bug you see there are many more ...MANY that you don't see....kind of like termites. Personally  (and respectfully Bill) I think you're a little worried unnecessarily about the pesticides.  The way I look at it, this stuff that we buy over the shelf, is not designed to be toxic to humans just by being in close proximity to it.  Probably not good to mix in the Cheerios but spraying in the home, I'm thinking the EPA and the makers would take home usage into account when deciding the strength of products. That's just my thoughts.

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Please forgive my ignorance and this might be a stupid question but here goes. If the bugs you have found and benign and harmless why are you going through so much expense and labor to get rid of them? Are the boards that valuable? If I were that worried about it, I think I would invite the family over and have a good old fashion wiener roast. Please fill me in, I'm sincerely curious.

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Good question.  Killing the tiny bugs i found isn't the motivation for the project.  I initially thought the bugs i discovered were powder post beetles.  I read many nightmare stories while doing some research on them.  They lay eggs that can take upwards to years to mature and exit the wood.   I've accumulated somewhere in the ballpark of 2000 board feet of oak, maple, cherry, and walnut - all of which was air dried outdoors.   There's about $800 invested into the lumber and while that's not the end of the world, it's still sizable enough to not want to just burn it away.  

 

After doing all that reading i figured it best to spend the ~75 to build the little sterilization chamber just to be on the safe side.  I'd hate to build my upcoming projects only to have bugs emerge from it after they're complete.  Going forward I'll use it anytime i buy wood just to ensure that it doesn't pose any problems.  

 

The first batch is still in the chamber. So far it's up to 105 in the far lower corner and 120 at the roof near the middle.  It's definitely taking longer than expected.  For the second batch i'll likely buy a couple more sheets to place under the pile as i think the concrete floor is absorbing a good bit of the heat.  Also, i noticed that the wood is sweating out a good bit of water.  I'm wondering if i should toss my dehumidifier in there next time to try to ward the condensation due to the high humidity in the box.  Though, i also don't want to strip the wood of it's moisture only to have it regain it as it acclimates back to the shop's humidity.

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It does kind of function as a kiln, but i think it'd need some tweaks to be truly effective as one.  I think kilns are normally kept at a lower temp and only increased to high temp on the last day for the sterilization process.  They also have a lot more airflow in order to mitigate the high humidity that's created by the lumber.  There are a handful of DIY wood kiln instructions out there for those that are interested.

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RESULTS of the chamber:

So i let it run for a total of 31 hours.  The lower thermometer got up to 117F and the upper one was up to 145F.  It was still climbing, but only about .5F every few hours.  It was at ~115F for roughly 12 hours

 

Mistakes / Ways to improve:

  • I should have used 2" insulation.  The outside of the foam felt warm to the touch, so it was surely leaking warmth through the insulation.  As a test, i put a roll of paper towels on the board and left it there for a couple hours.  When i picked it up the one side of the roll was much warmer than the opposite side indicating the insulation was too thin.
  • Not enough airflow.  That little fan for the fireplace heater was enough to move the heat down to the other side of the chamber, but it wasn't enough to cause the upper air to mix with the lower air.  This lead to a fairly extreme temp difference from the top of the chamber to the bottom.
  • Poor joints.  It seems i should have used some kind of internal support afterall.  Or possibly just re-positioned the top piece so that it was sitting on top of the sides instead of simply taped to the sides in a floating position. Kind of a duh moment when i saw that the tape eventually failed and the top dipped down.  Coincidentally, this was also where i used the shortest pieces of tape. 
  • A larger or additional heat source could be used for faster operation. Though, with improved insulation i don't think it'd be truly necessary.
  • Using insulation on the floor would also speed up the process since the concrete absorbed a good bit of the heat.

Areas where there was air escape caused a significant amount of condensation when it reached the cooler room air/surfaces.  I suppose this is to be expected, but it did cause a few areas of the blankets to get saturated.  The wood inside was on stickers and appears to have remained dry.  The water was only at the base of the chamber walls where there was some air leaking in/out.  The interior walls of the foam were dry on the inside, so i don't think there was any real moisture threat to the lumber.

 

 

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From a quick look I think spacing the stack higher off the floor so the gap below and above is roughly equal then adding fans above and below blowing in opposite directions to distribute the heat might help. I got 2" foam at "Depot" to use under my track saw . Foil tape for ductwork works well on seams.

Sorry the learning curve is so rough on your project.

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