setting pitch

[wooddog]

You all must have covered this before, but I'm new to pine pitch, I'm used to working with ash, birtch, and maple, and other hard woods. I'm helping mill pine with pep when I can, and setting pitch seem to be a  topic. Pitch is the sap in the wood? I think, what temp will It show up air dryed wood? I have made stuff out of pine before I think that was only air dryed, have finish it and don't seem to have a problem with it.

[Minnesota_boy]

A lot depends on the species of pine you have.  Red pine will bleed pitch after it's air dried every time the temperature gets above the temperature it dried at, such as a piece from the center of the stack being out in full sunlight on a hot day.  Every knot will be stricky and have beads of sap on it.  White pine will do the same except perhaps worse.  When you put these pieces in a kiln and raise the temperature enough, the pitch is set and bleeding stops.

Jack pine seems to be less of a problem, although it can still bleed on a larger knot.  It takes a temperature change to above what the piece has seen before to make the pitch run again.

[Chet]

Normally you may asume, pitch will be set at what ever the highest temperature the lumber has been exposed to for 24 consecutive hours.

[wooddog]

Ok i'm working with white pine. would the pitch set If the wood is in a buliding in say july or augest when we get temps of 80 to 90F , would the pitch set to that temp even if the temp drop at night and how long would it have to stay there?

[Chet]

No....  that 80 to 90 temp will probably be only for a short time of the day.  I should have also mentioned earlier that the wood needs to be at those temps, not just the air.

[Brad_S.]

The temp used most often is 160 degrees. Even if the pitch were to be set at 90 degrees, sun shining on the wood could raise the temp well beyond whatever the ambient air temp is and get the pitch oozing again. I've read that even at 160, sun shining through a window may exceed that temp.

[Tom]

Wooddog,
You need to understand what is happening when you "set" pitch.  You are getting rid of all of the volatile chemicals that will liquefy at that particular temperature.  You can raise the temperature and not leave it high enough long enough and still not get all of the chemicals set.


If you had a jar with 6 chemicals in it, all of which would evaporate at separate 20 degree intervals, you could perform this test.

Heat to 90 degrees   the first chemical will begin evaporating.  After 30 minutes, it is gone.  It was the only chemical in the jar that became volatile at 90 degrees so relative to that chemical (temp) it is set.

The other chemicals haven't been affected yet because the temperature wasn't raised high enough for them to become volatile.

Now raise the temperature 20 degrees.  The chemical that becomes volatile at that temperature begins to evaporate.  In two hours it is gone and the chemical is set for that temperature.  

At 130 degrees another chemical is evaporated.

At 150 degrees another chemical is evaporated.

Each level of temperature will get rid of the chemical that is volatile at that temperature.  

The catch is that the temperature has to be held long enough for ALL of that chemical to be evaporated to reach a point of its being "set".

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A board raised to 110 degrees will have its pitch set.  But, it will be set only for those chemicals that became volatile at 110 degrees.   If you put the board in the window and the sun heats it to 150 degrees then there will still be chemicals present that will cause the sap to run.

If you never reach  150 degrees in your house, then setting the pitch at 160 degrees is sufficient.

If you have a house fire and the temp raised above 160 degrees, the sap will run.

That's why one has to be definitive when he talks about setting sap.  Commercially, sap is set above the temperature that would be expected to be reached in a home, or in the place it is expected to be used.

[woodhaven]

Well said, Tom

[breederman]

sooo... if I put air dried spruce in my furnace roomand shut the door for a few days, I could use it for panaling the rest of the basement where it would never gets as hot as it got in the furnace room??

[jimF]

breederman,
The basement room may not get that high of temperature, but is there a hot water pipe that will get a small area hotter.  Or will you use it in a cathedrail ceiling with southern exposed window in the room, that ceiling can get very hot.

To make the actual process more complicated but more accurate, the lower volatile chemicals will make the higher volatile chemical ooze at lower temperatures than if they were pure chemicals and not all of the lower volatile chemicals will evaporate at the temperature at which they would as a pure chemical.  The percentage present of each determines the actual temperature at which all this oozing and evaporating will occur. Ain't chemistry fuuuun!?

[breederman]

It is a small room with a wood furnace in it. If I shut the door on a cold day when house is calling for heat it probably will get to 90 degrees or more.
 I want to use it on the ceiling of our basement /family room,no sun.

[jimF]

90 degrees is air drying - no pitch setting there.  In such a small room you will have alot of checking/cracking for the very dry heat.

[jimF]

One more point to understand about pitch setting.  If wood is heated to say 120F and some of the pitch compounds evaporate, that does not mean the pitch will not get soft and flow if reheated to 120F.  Think of water you can have water heat to 120F have some evaporate but it is still liquid and it will flow.  Therefore the pitch will still flow if it is heated to below the temperature at which it was "set" at.  Ain't chemistry fuuuun!

[Tom]

That's why that temperature must be held to "boil off' all the volatiles available at that temperature to consider the pitch to be set.

If you boil a pot of water until all the water has gone away in steam, that pot won't boil again ......less you put some more water in it. 

[brdmkr]

90 degrees is air drying - no pitch setting there.  In such a small room you will have alot of checking/cracking for the very dry heat.

I have not dried any pine, but I was under the impression that pines were pretty forgiving in terms of drying (e.g., that you could dry them quickly and set pitch with minimal checking).  Would anyone care to chime in on this?

[Tom]

The results depend a lot on the type of pine.   It does dry fairly fast but can be ruined if the sticker stack is built wrong.   I think the reason that end splitting, and such, is minimal, relative to other woods, is because pine is self-sealing.  The sap at the end of the log congeals and forms as good of a sealer as anything you could buy.

[jimF]

Tom,
Go back to my first post yesterday.  Water is a pure substance, pitch is not.  All of the lower volatiles are not "boiled off".  Also, the compunds that evaporate at higher temperatures are fluid at lower temperatures and even lower temperatures with the not completed evaporated lower volatiles.  The percentage of each influences the rest.  Even with time lower volatiles do not evaporate.
Brdmkr,
If surface checks and cracks are acceptable then you don't need to worry.  One reason pine is dried so fast when used for dimensional lumber is because surface checks are not a defect in dimensional lumber, they are present though.

[Tom]

Well, JmF, I'll rely on your expertise.  You'll find that a lot of comments on the boards holds tongue in cheek jokes and simplifications.  It has been my understanding that  the setting of pitch is a term that signifies that the temperature has been raised significantly to rid the lumber of those volitiles that become liquid below that temperature.   I'm sure you know what you are talking about and I lack the formal education to dispute what you are saying or even understand some of it. 

[DanG]

I think I'll just go along with Tom's explanation until someone comes along who can explain it better.  Merely telling someone that they are wrong doesn't accomplish very much unless one can back up one's statement in a manner that the audience can understand.

[getoverit]

I've spent over 25 years distilling pine sap (turpentine)... Tom, you're exactly right.

[Don_Lewis]

Pitch setting has to take into account what you will be doing with the lumber. If you are making a piece of pine furniture or flooring and sanding it a lot, the temperature under the sanding belt will be hot enough to quickly load the belt.  160F is the accepted temperature for that use of the lumber (not the air) for about 24 hours. The time depends on air temperature though.

[Don P]

I'd like to understand this well enough to simplify it. I've understood pitch to be sorta like crude oil. If you had a tower to condense the volatiles as the were driven off there would be a range of by products that condense at different levels. If I'm anywhere close there must be a list of what is driven off at each temperature level. Is there a point, short of amber, where it is truly "dried up"? I guess the analogy would be, does it ever become thermosetting instead of thermoplastic?

[brdmkr]

I thought Tom's explanation sounded a little like tempering metal.  Once metal is tempered, as I understand it, it will not loose its temper until it is heated above the temper temperature.  Also sounds somewhat like frational distillation as mentioed above.  Either way, sounds like if pine is exposed to temperatures above that used to set pitch, it may weep.

[beenthere]

Interesting thread, and some of it is even understandable.  Thanks Tom.
 

[Ianab]

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Is there a point, short of amber, where it is truly "dried up"? I guess the analogy would be, does it ever become thermosetting instead of thermoplastic?
I dont think so, if you take your piece of kiln dried pine and get it REALLY hot, like on a fire, the pitch will start running out again.
I think the crude oil analogy is a good one, crude oil is usually a waxy sort of sludge, if you let all the naptha and petrol evaporate out it will 'set', but it can still be melted if you warm it up. Heat it and take out the kerosene / diesel weight components then you have bunker oil that is a solid at room temp. One step more is tar, pretty much a solid, but even than it will melt in the sun on a really hot day.

Cheers

Ian

[Den Socling]

Jim,

I'm sure that there are bonds between compounds that affect boiling point but don't you agree that Tom's explanation is basically correct? Guess what happens to 'pitch' in a vacuum chamber. I've taken pine that was dried to a max of 140'F in a vac chamber and heated pitch pockets to 190 and they stayed solid.

Den

[jimF]

Tom's explaination is the first step to understand what is going on.  But there is a strong interaction beteewn the pure chemicals in the mixture.  The remaining mixture will melt and flow at a temperature lower than the maximum temperature at which it was previously exposed to.

When it is exposed to the maximum temperature also influences how effective the "setting" process is.  If performed early in the drying cycle(when the MC is high) it is more effective than later (when the MC is low) because water is part of the mixture and it's boiling point also influences the boiling point of the mixture.