Air dried lumber and insects?

[Phil Thien]

So I found someone that has 20-year old air-dried lumber stacked in his barn. He thought it was walnut and beech. There are absolutely some pieces of walnut, but some of the stuff in the stack is awfully orange, and the fingernail test may indicate it is something other than walnut (but I'm not sure). And I'm not sure there is any beech, either, for that matter. I just didn't think beech was very common around here.

I took a few pieces home to inspect them and found some insect holes here and there. Mostly towards the edges. The holes are about 1/8" x 3/16", and are from 1/8" to maybe 1/4" deep.

I cannot see any insects.

I'm not sure it is safe to bring this stuff into my basement shop or not.

What type of insect would I have to be concerned with? What should I look for?

Any tips?

[Matt Ranum]

Any sawdust piles by the holes? If not they were probably made while it was in log form. If cut logs sit for a long time before they are sawed insects will invade the bark. The softer the wood the worse it seems to me.

If there wasn't evidence of recent chewing I wouldn't worry about it, and you could always apply an insecticide.

[Barry Vabeach]

Phil, if the lumber was heated to above 130 ( which would be true for klin dry not air dry ) any powder post beetles that were in the tree when the lumber was milled would be killed. You might want to do a search on powder post beetles, my guess is the larve can live a long time. I bought some air dried walnut recently and mixed it with some other lumber, and then found some holes and some dust - I ended up building a small solar kiln and put any lumber that was near it in the kiln ( it took several cycles) and heated it above 130 for a couple of hours. While not seeing any sawdust means it isn't active, I would hate to finish a project and a year or 2 down the road find bugs eating their way out. Barry.

[Phil Thien]

Are there any plans for small "kill the bugs" kilns that would do maybe 10-12 boards at a time? I'm thinking a 8 to 10' long box that is maybe 16" high and 16" wide, with some sort of thermostatically controlled heating element?

I've seen the solar kilns, but they are large and this time of year I'd need a lot of supplemental heat anyhow (days are getting short and dark here).

[Scott T Smith]

Are there any plans for small "kill the bugs" kilns that would do maybe 10-12 boards at a time? I'm thinking a 8 to 10' long box that is maybe 16" high and 16" wide, with some sort of thermostatically controlled heating element?

I've seen the solar kilns, but they are large and this time of year I'd need a lot of supplemental heat anyhow (days are getting short and dark here).

Phil, if the lumber is already dried then you don't need to worry about managing the relative humidity - only getting the temperature up. Some folks use an old refridgerator with some 200 - 300 watt light bulbs installed inside.

Another option is to stick the boards up in your attic for a few weeks, if you're in a warmer climate. Or, you can buy some tekfoil (www.farmtek.com (http://www.farmtek.com)), and build a tent with some type of heat source inside.

[Barry Vabeach]

Phil, the one I built wasn't that much bigger. I had the advantage of discovering the problem in the summer so solar was the way to go. If I needed to do it now, I would buy the rigid insulation sheets they sell at Lowes ( 4 x 8 panels in various thicknesses ) and put it together with tape and build it like a steam box and put an electric heater to feed it - ideally - feed the heat in the middle and make some controlled venting at each end. IIRC, you need 130 for a couple of hours for 4/4 lumber - as temp goes up, the time needed drops - so 140 might only need 1 1/2 hours.

[David Christopher]

sounds like alot of work for something a household insectacide would take of

[Barry Vabeach]

David, I think any insecticide ( other than fumigating) you use will kill the bugs on the surface but won't kill the eggs or the larve. THis site promotes the sale of some of the pesticides, but does point out that it is tough to kill the eggs.

http://www.powderpostbeetles.com/ This is an article from the lumber perspective http://www.palletenterprise.com/articledatabase/view.asp?articleID=2890

[roman fedyk]

That is correct. Pesticide kills the live bugs but not the eggs. When they hatch they eat their way out. If the insecticide is still active they would die. However that depends on how long it is before they emerge. Pesticide is not a forever thing and sometimes these critters take a year or more to emerge.

Then even if they do emerge and die, you are left with a lot of dead bugs and exit holes all over your fine furniture.

Heat is the best way. But the wood needs to be heated to at least 130 degrees not the air in the kiln.

[Scott T Smith]

Heat is the best way. But the wood needs to be heated to at least 130 degrees not the air in the kiln.

You also need to leave the wood inside the "kiln" long enough for the CENTER of the board to reach 130F for several hours. Just having it at 130 for two hours is not enough time for the center of the board to get that hot. Personally, I use a 24 hour cycle in my kiln at the end of the cycle for sterilization.

The thicker the board, the longer it needs to cook.

[Barry Vabeach]

Scott, I don't disagree with your statement about holding the temp in a kiln, and in general think 24 hours is the preferable if it can be done, but IRC I read a paper that did some testing and found that holding 130 at the center for an hour or two killed the bugs - and for 4/4 lumber, that only required a total of less than 4 hours. I augmented a solar kiln with heaters, and hit 130 pretty easy between 1 and 5, but before and after it dropped way down and there is no way I could make it 12 much less 24 hours.

[Yitah Wu]

Just occurred to me that during the summer a large car / SUV would easily work as a kiln, assuming you could fit the pieces in.

[Scott T Smith]

Scott, I don't disagree with your statement about holding the temp in a kiln, and in general think 24 hours is the preferable if it can be done, but IRC I read a paper that did some testing and found that holding 130 at the center for an hour or two killed the bugs - and for 4/4 lumber, that only required a total of less than 4 hours. I augmented a solar kiln with heaters, and hit 130 pretty easy between 1 and 5, but before and after it dropped way down and there is no way I could make it 12 much less 24 hours.

Barry, thanks for your note. I'm pretty conservative in my approach, as I don't want my customers to ever experience any problems.

The USDA "Dry Kiln Operator" handbook contains a lot of great information about kiln drying. Section 7 of the handbook addresses lumber sterilization, and table 7-31 of that chapter contains kiln schedules for killing powder post beetles and their eggs.

According to the handbook, at 130F it requires the kiln 10 hours to reach the sterilization set conditions for 4/4 lumber. This takes into account "cold spots" in the kiln, etc. You add 2 hours for each additional inch of wood thickness.

In my instance, I neglected to mention that I'm conditioning the lumber at the same time as sterilizing it, hence the longer than 10 hour recommended timerframe.

As an interesting "aside", per the USDA manual it requires 46 hours to sterilize at 125F, and only 3 hours to sterilize at 140F.

One comment re your solar kiln - have you considered covering up the solar panels with something like Tekfoil when you're sterilizing? With your auxilliary heaters, during the sterilization process if you covered the inside of your panels with a reflective product like Tekfoil I'll bet that you could come closer to holding the 130 targeted temp.

If you'd like, I can send you a .pdf file of the above referenced handbook chapter for your records. It contains some other good information re drying schedules, defects, etc.

Regards,

Scott