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Setting the Pitch - Temperature Guidelines

Started by foresterstan, September 29, 2016, 10:59:45 AM

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foresterstan

I have been drying softwood (mostly Larch and White Cedar)  in a Koetter kiln for a few years.
the max temp on all the schedules provided with the kiln is 60 degrees C (140 F)
most of the stock has gone into indoor trim and panelling.
recently some of the window trim that is in direct sunlight began to ooze pitch.  I looked it up and found that most people set the pitch at 160 F (71 C) which is quite a bit hotter than I have been going with my schedules

I understand that softwood will leak pitch when it reaches a higher temperature than it was at the hottest stage of the schedule.
is there anything magic about 160 F or is it just a good benchmark?   
even if I run the schedule up to 160 F will that protect me from the direct sunlight issue?

I would appreciate any advice...

-fs

Den Socling

It's just a bench mark. It's as you say - the pitch is hard until it reaches a temperature higher than the final temp in the kiln. I have pitch on the heating plates in my vacuum kilns. The combination of heat and vacuum has made that stuff hard as rock. It's like amber.

foresterstan

thanks for the quick response... 
any experience with the direct sunlight thing?

it's going to be a pile of work to modify my kiln to hit 160, just wondering if it will really make a significant difference to the end product...

-fs

GeneWengert-WoodDoc

Clarification.  At 160 F, or any other temperature, you will evaporate that part of the pitch that VAPORIZES at 160F.  However, there will be a lot of pitch that flows and is liquid at 160 F...such pitch will not vaporize until a higher temperature is reached.  At 160, some pitch is solid, but a lot is not.  Pitch has so many different chemicals that the hotter you go, the more that vaporizes.

Now, when the wood cools, let us say 10 F to 150 F, some pitch becomes more solid, but some pitch that would have vaporized at 170 or 180 or 190 F etc., still flows at 150 F but not as fast. 

Perhaps at 110 F, all the pitch will be solid and not flow fast enough to matter.  However, as you have seen, wood can get over 110 F from sunlight, or in a hot attic, or near a stove pipe, etc.  Plus, I f you treated under 160 F or did not apply the heat throughout the piece for a long enough time, there will be more pitch that flows under 110 F.  So, the best temperature for setting the pitch is 180 or 190F.  Some people, especially solar or DH, cannot achieve that temperature so they try for 150 or 160 F, but this is,not as effective as 180 or 190 F. Some people do not heat the wood long enough...for 1" and 2" pine, actual size 1.8", at 160 F, ar least 36 hours' at 180 F, 24 hours.

Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

alanh

Not that this is any help to your question but I have "store bought" pine I used on an outdoor kitchen project a few years ago and this summer the heat and sun caused pitch to ooze from a couple knots...

Den Socling

The store-bought may have been heated high enough but I'd bet it wasn't up there long enough. Like Gene says, VOC's are being evaporated during the process.

foresterstan

Thanks all for the input, very educational.
I guess most of our product has gone into lacquered panelling, so the finish must hold in a fair amount of the pitch.
probably because of this I have only had a few cases where the pitch ran out of larger knots in direct sun.


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