Sawing and Drying

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heat treating

6/27/19       
Jonathan Cook Member

several weeks back I staked with 1 inch spacers 2 inch pine boards in an insulated room. I had a blower sucking air from the top and blowing it under the pile. I had a thermostat attached to 2 torpedo heaters set at 170. They were blowing into the room through double walled pipes. I started early Saturday morning and achieved temperature late Saturday. I kept going until Sunday evening until the internal temperature of one of my board in the center bottom of the stack registered between 132 and 133 for several hours.
My target was 133 for 30 minutes, but I was exhausted from supervising the project all Saturday night and was afraid that the boards were going to warp too badly from all the heat and over drying. I thought surely over 132 for hours would be good. Then I edged and planed and polyurethaned about 50 of the boards because I want to use them to anchor over the purlins of my timber frame. Now I see fresh powder. also I sprayed these boards with timbore prior to the heat treatment, Partly to make sure they would not get reinfected during the process of edging and planing I imagine the timbore was mostly planed off prior to polyurethaning. This is very aggravating. Some of what I read says the life cycle should be interrupted simply by sealing the wood with paint or polyurethane. That eventually the adult will emerge and new larva will not penetrate the sealed surface. But I think the life cycle of some of these pests is years.

On top of this my timbers for the timber frame have been treated with timbore as well but can certainly not be heat treated as that would take weeks. They were fully air dried for years then recut to correct any twisting and sprayed with timbore. I am planning to sand them lightly and then finish them with out planing. I am hoping any bugs that might emerge through the timbore will die and no new larva will make it through the finish to start a new cycle. I have barns made with rough cut lumber with some signs of bugs that are still standing 30 years later and I hope timbore and polyurethane will eventually end the cycle in my house I am trying to build. I hope there is some advice here other than a huge bonfire. I could try reheating at least the boards with noticable powder once they are polurethaned. Maybe the polyurethane would prevent over drying and warpage, but I am afraid they might develop an unacceptable crown. They presently will fit together nicely since they have been edged. That still leaves my timbers. At least the timbore has not been planed off of them. I could spray the rest of the 2 inch boards with timbore once they are planed and then put them back with a dehumidifier prior to polyurethaning them, but it will be time consuming and they might warp again with the moisture changes. Thanks for any help

6/30/19       #5: heat treating ...
GeneWengert-WoodDoc

Spraying Timbor can, if enough chemical is concentrated at the surface, provide a barrier to the entry of new insects. If the wood develops a crack, there will be untreated wood exposed.

When spraying, you can determine the amount of wood you sprayed and the amount of chemical used per square foot or per cubic foot of wood. In other words, a single, light spraying provides limited protection from a new infection and no benefit for existing activity. Of course, the planing removed the timbor, which is now in the shavings.

But, even if you did get a new infection, it would be weeks before seeing the exit holes of any new insects. So, we know that the new powder, called frass, is from old insects. I assume you are certain that the frass is not just frass from the old holes, but that these are new holes. I assume that the polyurethane was thick enough and covered the old holes you exposed when planing. Can you see the new holes that now come through the polyethylene and the sharp edges of the holes, using 10x magnification? This assures us that they are indeed new holes, as a thick coating of poly would have filled or partially filled the holes. Of course, a very thin coating is likely not 100% effective on new insects.

If indeed you still have insects in wood you heat treated, then you apparently did not reach the magic temperature of 133 F. In fact, in pine, you could have ambrosia powderpost beetles, old house borers, and more.

What is the size of the hole?

Because you planed the wood, did you expose long tunnels that would have been near the surface? Is the frass coming from these?

7/1/19       #6: heat treating ...
Jonathan Cook Member

I dont think it is a new infestation as I polyurethaned the board quickly following planing and had them stored in the heat chamber with timbore on them prior to planing. also I would not think there has been enough time for it to be a new infestation. Some of the boards did have exposed running tunnels after planing and these are the ones with the most noticeable frass. They only have one coat even though most of them have 2 because I think I will plane the polly off and apply timbore. some boards have very little or no holes and some have no sign of fresh frass

the holes are different sizes, but mostly anything active seems pretty small

I still have a stack 12 layers high of 2x10s 7 feet wide and 14 to 16 feet long sitting in my heat chamber. I have edged and planed and polyurethane about 5 rows. I have a dehumidifier in there set on 45 % i could try heating them again but feel like I already caused some warpage the first time. Should I try again? I think I set my cut off at 170 degrees and the internal temperature of a center board toward the bottom of the pile was around 132.5 for hours. Assuming my probe was accurate is 170 good but just longer? Should I plane then use timbore again and then dehumidify and then poly and feel that with timbore and poly the infestation cycle should eventually be broken.

Also I have some issues with my timbers which I have sprayed with timbore. I was going to put a finish on those, but think maybe I will not put a finish on them so I can keep spraying them as needed during the construction phase and after as needed for an extended time?

Thanks


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