Stabilizing Wood: Physics, Chemistry, Materials, Techniques, and Performance: "Just the facts Man"

[Lotmom]

Correct!

Problem with freezing is you may split the wood as the ice expands?

From what I understand, freeze drying sublimates off the water and doesn't cause structural damage. See this guy's videos:

 

[Cushing H.]

From what I understand, freeze drying sublimates off the water and doesn't cause structural damage.

sort of. freeze drying preserves the bulk structure and shape of the thing being dried (once that thing is frozen) (you are right, because the water sublimates versus melts), BUT to get to the "frozen water" part, you need to first freeze the thing. when water freezes, it expands, and can do two things: is can cause bulk damage (like splitting - of wood or a glass the water is in), AND the ice crystals at a much smaller level act as "spears" or "many small knives" that, especially for food which has lots of cells in it, actually rip to shreds the cell walls. That is why frozen food never has the same texture as fresh - it has been ripped up at the cellular level. The faster you freeze the less the damage (because you get more but smaller ice crystals - but the damage is still there....

 

[Willie71]

sort of. freeze drying preserves the bulk structure and shape of the thing being dried (once that thing is frozen) (you are right, because the water sublimates versus melts), BUT to get to the "frozen water" part, you need to first freeze the thing. when water freezes, it expands, and can do two things: is can cause bulk damage (like splitting - of wood or a glass the water is in), AND the ice crystals at a much smaller level act as "spears" or "many small knives" that, especially for food which has lots of cells in it, actually rip to shreds the cell walls. That is why frozen food never has the same texture as fresh - it has been ripped up at the cellular level. The faster you freeze the less the damage (because you get more but smaller ice crystals - but the damage is still there....

Thanks for clarifying that. This is part of why we can’t freeze a body and revive it. The cells are torn apart.

 

[Lotmom]

Hmm... There must be a way to freeze wood fast enough that it wont break. Here in Canada, its not incredibly common to see trees split from freezing in the winter, I think this warrants extra investigation... It's been humid here, maybe ill toss some walnut or birdseye maple in the freezer and compare to an unfrozen piece...

 

[Cushing H.]

Here in Canada, its not incredibly common to see trees split from freezing in the winter

Live trees?

 

[Randydb]

I’ve been harvesting wood this month, and putting aside some nice stuff for guitars, tables, and knife handles. I’ve got a few trees with trunks over 24” wide!

This is my first stack to start drying. The bottom is a silver maple planted in 1962, by my uncle who passed away about a year and a half ago. I’m making at least three guitars out of this, as we have several pro musicians in the family. The top 6 pieces are the poplar. I cut down two more threes already, but the bases are still in the wooded area, as it rained heavy since I cut them. I’ll get them out this week. The bases almost all have spalting and or heavy curl. The top two pieces are crotch poplar for hopefully one piece guitar bodies. I’m going to assemble a passive solar kiln for drying as time permits.

790D384B-7241-49D6-87E8-2F09F4F6551C by Wjkrywko, on Flickr

I’m in Alberta.

I live near Vancouver in BC. Spent 8 years in Alberta. Things are a lot less humid there. I used to get nose bleeds in the winter from the dryness.
That is another thing that comes into play. It's difficult to air dry wood here below 9%. Dry on the coast is considered 9-12% I know you can get much lower moisture content in Alberta.

 

[Cushing H.]

I live near Vancouver in BC. Spent 8 years in Alberta. Things are a lot less humid there. I used to get nose bleeds in the winter from the dryness.

Yeah - minnesota is similar in the winter: it is common when the temp really falls to see a light sprinkling of small pieces of ice/snow falling from an absolute crystal clear blue sky. This is moisture in the air freezing out and falling to the ground. Probably why after many years some of my high-end knives are showing handle shrinkage. (the 35 year old Sabatiers with phenolic handles are doing just fine)

The thread on cooking steaks whetted my appetite fir one. Last night got a nice aged ribeye, put the grill (sorry, gas) on high. When temps exceeded 750F put the steak on. Nailed it a pefect medium rare. Pulled out one of my 15 year old Laguiole steak knives with Ironwood (i believe) handles. Darned if THEY have not also shrunk so the tang is protruding all around (pins still seem ok though).

Im beginning to wonder if my original question on “just how stable is stabilized wood?” Is going to end up being an ambient/environmental issue in the end...

 

[Lotmom]

Live trees?

Yes. In the winter, much of the sap goes into the roots to protect it and keep some nutrients stored, so it's very similar to deadwood or dry greenwood

 

[Cushing H.]

Hmmm.. the reason I ask is because it is my understanding that live wood (including trunks and branches) do not freeze (in the form of forming ice crystals). they might fall below "freezing point" ... but there is enough impurities in the sap that the freezing point is depressed. also, there IS some internal heat generated by metabolism so that the insides is kept warmer than the outside air (this is why snow falls off branches, and the snow melts away from the trunk before the surrounding snow melts.....

 

[Cushing H.]

just a little data to add to this (to help people with expectations). Just for yucks I placed single scale-size pieces of walnut and purple heart into that food dehydrator at 145F (BTW, wax melts somewhere below 145 :-( , and weighed them on a daily basis. (also BTW, the purpleheart held up to the stressed conditions well - not a sign of cracking). The weights over time look like this:

so clearly, the walnut dried as much as it was going to in one day. The purpleheart, however, after 4 days in the dehydrator is still losing weight, and does not look like it is leveling off. Granted, the purpleheart, I believe, was wetter to begin with (something like 14% versus 9% for the walnut) ... but as a percentage weight lost versus time the purpleheart is obviously much slower than the walnut. I do not know if I can keep this going (my wife objects to the sound of the dehydrator in the kitchen) ... but will try to see where this goes.

Just a little bit of reinforcement that, if you are drying wood for stabilization - you should generally be thinking multiple days for the process.....

 

[Randydb]

Hmmm.. the reason I ask is because it is my understanding that live wood (including trunks and branches) do not freeze (in the form of forming ice crystals). they might fall below "freezing point" ... but there is enough impurities in the sap that the freezing point is depressed. also, there IS some internal heat generated by metabolism so that the insides is kept warmer than the outside air (this is why snow falls off branches, and the snow melts away from the trunk before the surrounding snow melts.....

Local forester/researcher that I know was saying that trees get more sugar in their sap in winter which lowers freezing temp and also get rid of a lot of their moisture content (less moisture=less expansion with freezing) and enter a dehydrated dormancy period. This year we had a very warm spell in January in our area and a lot of the young douglas fir and salal came out of dormancy. Then there was a very cold spell after that in February and a lot of them were affected and parts of the plants were killed because of it. A lot of them have had new growth since, but the foresters were watching and unsure at first if the trees/plants would die.

 

[Cushing H.]

trees get more sugar in their sap in winter which lowers freezing temp and also get rid of a lot of their moisture content (less moisture=less expansion with freezing)

Interesting - i did not know sugar content rose in winter. Makes sense as a protective mechanism.

 

[Cushing H.]

Next issue:
What gets in the way of filling the porespace with resin? – AIR

This is an easy and fast discussion. Ultimately, the porespace in the wood is “closed” in the sense that since resin will be pushed into it from all sides, ultimately everything converges into “dead ends” inside the wood (not necessarily in the center of the wood, but probably mostly there, as the resin is pushed in by pressure from all the outside surfaces, converging towards the center of the piece). As the resin is “pushed in” to the wood, the remaining air is (more or less) pushed ahead of the resin, and gets compressed in those “dead end” spaces.

This has two effects. 1) the remaining compressed air will block further penetration of resin into the pores, limiting the amount of porespace that is filled by resin. 2) you might THINK that by putting a higher pressure on the sample (like the 4000 psi that K&G uses) you would compress the remaining air more and give you more resin-filled porespace. BUT, no matter how much pressure you apply (whether something slightly above atmospheric pressure in the home, or 4000 psi at K&G, when you release the outside pressure, that trapped compressed air will now push out and EXPAND (because the outside pressure pushing on it has been released), and in so doing, push the resin back out of the porespace (to the limit where the expanding trapped air is in roughly at atmospheric pressure).

There are some fine points around this having to do with viscosity of the resin (and elapsed time) which I will bring up later … but for now lets just leave it at the above.

(clarification of terminology: a “high vacuum” is the same as a low pressure. A “low vacuum” is basically a not very good vacuum – high retained pressure. I’ll try not to be confusing in use of terminology)

Roughly speaking then, the amount that residual air will interfere with ultimate retention of resin is proportional to the amount of vacuum you pull on the wood (i.e. fraction relative to atmospheric pressure) before you apply pressure (whether by just atmospheric pressure or by applying a higher pressure.).

In the end, a higher vacuum (lower pressure) is better – but extremely low pressures are increasingly expensive to achieve, and with the materials here basically impossible to reach. The problem is that old friend – adhesion – in this case of air molecules to all of the surfaces. Pull a vacuum, and that adhered air will start to come off the surfaces …. Increasing the pressure ! For example, very high vacuum systems (like scanning electron microscopes that I am used to using), have clean stainless steel surfaces everywhere. Even then, with a highly effective vacuum pump, they will take many HOURS to pull down to a really low vacuum.

We really can not do much about the air adhered to the surfaces, but we can do something about the quality of the vacuum pump we use (they get increasingly expensive as their ability to pull better vacuums increases). So – how much is good enough? Given that residual moisture (unless you take extreme measures) sits at about 5%, lets use that as a guide. Atmospheric pressure is 760 mmHg (14.7 psi). 5% of that value is 38 mmHg (0.735 psi). If you have a vacuum pump that can pull down to 38mm Hg, then you will have roughly 5% of the porespace excluded from resin penetration (in addition to the roughly 5% excluded by water – for a total of roughly 10% porespace exclusion.

Again, lower pressures are better – so best to drive to find a vacuum pump that can pull as low a pressure as you are able to afford (or that you are willing to accept lack of penetration of resin). Per the above calculations, you should be able to get a ballpark idea of what percentage of the porespace you are losing to trapped air depending on the actual vacuum level you are able to pull.

A couple final points:

1) When looking for a vacuum pump, pay attention NOT to the CFM (cubic feet per minute) ratings. This is totally separate from the vacuum level the pump can achieve, which is what you should be looking at (in fact, the pumps that are able to achieve the lowest pressures (high vacuum) have extremely low CFM capabilities. In the looking around I have done, many of the pumps appear to not readily publish their ultimate pressure capability. So beware, and look carefully at those ratings.

2) After you think you have pulled the vacuum level down to where you want it – WAIT. The air you have pulled out of the wood has not aerated the resin around it – you need more time for that vacuum to now get that air out of the resin. Also, you still have that issue of air molecules adhered to surfaces (both of the wood and the container). The more time you give it under vacuum, the more air you ultimately get out of the system. How long to wait? I would give it several hours, kept under as good a vacuum as you can during that time.

3) After that, then go ahead and release the vacuum, and allow the resin to get pushed into the wood. There is a TIME issue here, related to the viscosity of the resin, but that is mostly an independent issue, and I will talk about that later.

 

[Cushing H.]

Next up - Particulate....

What gets in the way of filling the porespace with resin? – Particulate

This is another quick one, but pretty important. From the earlier posting on the pore system in wood, remember that the typical pore sizes can be categorized into four basic ranges: 10 microns, some that are about 1 micron, some that are about 0.1 micron, and some that are 0.01 micron in diameter. Now … these are pretty small, and any particulate present will lodge in the pore “pinch points” (technically called pore throats) and act as “stoppers” in those pores. They will either completely clog the pores, blocking any resin penetration, or they will effectively make the pore throats smaller, greatly inhibiting the ability of resin to pass that point (next point will be on surface tension, which will make that point clearer).

So – any treatment that intentionally includes significant particulate will pretty much by definition only be a surface treatment of the wood, not a fully penetrating bulk stabilizing process. These are probably fine, as long as you know what you are getting: surface reinforcement only, not a bulk treatment.

As far as acrylic resin-based stabilization goes, you do NOT want particulate present – as penetration of the resin into the wood will be inhibited. There will, of course, be some particulate present … but you want it minimized.

Any particulate present can come from several sources: manufacture, handling, and storage.

As far as differences in manufacturing goes, I just would not worry about the differences between resins. It has been said that the professional stabilizers somehow have higher quality resin – and that they can get resin the home stabilizer can not. By and large, I really doubt that is the case. First of all, anyone synthesizing resin has got to be doing it on a large enough scale to make it economically profitable: a small-scale effort somehow exerting profound quality control would be EXPENSIVE (and it has already been pointed out that the commercial stabilizers are just not that expensive to process your wood through). I have confirmed that K&G does not synthesize their own resin – and I would very much doubt the other commercial stabilizers synthesize their own – it is far too technical and expensive a process. Also, actually it is easier to control the quality of a process with larger or continuous processes. All of the resins I have seen out there are basically in the same price range – which means they are all basically manufactured using the same level of quality control. When you do a search on the web, you are not restricted to seeing those resins just available to the “home” user – you see them all – small scale and commercial scale (sorry, but I have been doing these searches for professional sourcing my entire career…). And … there are just not that many different resins out there. Some are identical, but just re-labeled and re-branded from a larger manufacturer (for example BVV’s “American Made” resin – which is actually re-labeled “Stickfast” resin).

So far I have seen the following resins: Stickfast, Cactus Juice, BVV PC504/66 (relabeled Ultraseal), BVV “American Made” (relabeled Stickfast), Locke / Locktite Resinol 90C, Locktite Resinol 88C, and Paraloid B72 (it is quite possible I missed one or two – please let us know if I did so miss). What is telling, at least to me, is that the direct Chinese synthesizers of the Locke / Locktite resins indicate a production capacity of 4 tons/day, and a minimum order of 200kg. This gives an indication of the scale this stuff is synthesized at. A smaller sized manufacturer simply could not compete. Because they are all pretty much at the same price point – they are probably pretty much equivalent in terms of particulate content. They might have somewhat different formulations (for example Stickfast, BVV “American made”, and BVV PC504 all have viscosities of ~ 2 Centipois, whereas Cactus Juice is more viscous at 4-6 Centipois), and the Resinol 88C has a viscosity range of 5-20 cps … but the basic quality controls (as far as particulate goes) on these large scale synthesis processes are very likely equivalent. Because this stuff is synthesized in such large quantities – I would not be surprised at all if we actually have far, far more re-labeling of imported material than we suspect (thus reducing the actual variation in initial sources). For differences I would simply pay attention to the indicated viscosities – again, I will talk more about that later.

I would be more concerned about particulate introduced or created by handling or storage.

Anytime you handle, transfer, or re-package a material particulate can be introduced. The handling equipment might not be clean, or the transfer can be exposed to the environment (I doubt such transfers are done in an environmentally controlled “clean room” – as these are expensive to build and maintain. Also, the new receiving containers (gallons or thereabouts versus industrial steel barrels the original stuff is put in to) themselves are likely not fastidiously cleaned of particulate (doing so is an expensive and time consuming process). Unfortunately, with the likely few sources of materials, and likely common re-packaging / re-labeling happening, it will probably be difficult to determine up-front which resins have seen reduced handling and re-packaging. Probably the best option we have is, as a community, share experience with specific resins in terms of penetration (but this will be complicated by differences between individuals’ processes). Toss a coin on this one.

Above all, I would be most concerned about storage. For these resins, heat is the enemy in terms of particulate. Technically, these resins need an “activator” to start the polymerization process – but this is mostly a time/temperature thing. Even without “activator” present, there will be some reaction between monomers, especially at elevated temperatures. These reactions will create some level of particulate. Once “activator” is added to the resin, things become more dicey – and much more sensitive to temperature. Technically, even the activated resins will say you can store at room temperature, and that they are “heat activated” – but that does NOT mean that no reaction occurs at room temperature – the reaction is just slower (if you want, look up the “Arrhenius equation” regarding chemical kinetics). Again – any level of reaction begins to create particulate resulting from small monomers creating small “polymers”.

With that background, consider the following: much of this stuff is likely really sourced from China – and it is shipped to the world and to the US in big barrels on slow moving cargo ships. Temperature is completely uncontrolled. Even for un- “activated” material, there will be some level of particulate generation, especially when the ship hits tropical waters, and thus uncertainty in terms of particulate level. If you buy domestically a gallon of “activated” resin (whatever the brand), that gallon container is trucked around in non-temperature controlled truck trailers, which is the sun on the open roads will get HOT inside. More uncertainty. When you store that gallon container at home, you have more control, but again, even at room temperature, there is some level of reaction going on.

So, how to deal with all this? I would recommend the following: I would look first to domestically manufactured resin (it sees less exposure to temperature extremes when sitting on a ship for months). Second, use only non-activated resin, and add the activator yourself when at home (“non-activated” resin sitting in a hot truck on the highway will be much less sensitive to polymerization reactions than “activated” resin sitting in that same hot truck. Third, when you get your resin at home, whatever the source, store it in the refrigerator. All chemical reactions speed up at higher temperatures, and slow down markedly at lower temperatures. The difference in reaction rates between room temperature and refrigerated temperature depends on the specific system (and we do not currently have enough information on this one), but it can only help. (aside, it is quite possible that “freezer” conditions might be ok and thus even better … but we do not know enough about the resin to determine that. Has anyone out there tried storing your resin in the freezer – and what was the result?)

This turned out to be longer, and more “stream of consciousness” than I thought it would be – but hopefully it makes sense.

I think in the next posting I will try to tackle “surface tension”. This is probably our biggest issue to full resin penetration (but wont know until I crunch some numbers) … and also the most misleading and difficult to understand (it definitely requires pictures ). But once understood, it is really cool, and will help explain a lot about the application of pressure during the impregnation process…..

 

[daizee]

[content no longer relevant]

 

[Cushing H.]

Super interesting. Did you mean "non-activated" vs. activated in the above sentence?

Oops. Thank you for the catch. The sentence has been corrected!

 

[Alex Topfer]

I think there is also the suggestion that you buy resin in the smallest lots you can. no point buying a 50 gallon drum if you won't use it quickly. edit: this is what i do with epoxy glues. so far i use ~50ml a year, so i just buy 25ml every 6 months

This has two effects. 1) the remaining compressed air will block further penetration of resin into the pores, limiting the amount of porespace that is filled by resin. 2) you might THINK that by putting a higher pressure on the sample (like the 4000 psi that K&G uses) you would compress the remaining air more and give you more resin-filled porespace. BUT, no matter how much pressure you apply (whether something slightly above atmospheric pressure in the home, or 4000 psi at K&G, when you release the outside pressure, that trapped compressed air will now push out and EXPAND (because the outside pressure pushing on it has been released), and in so doing, push the resin back out of the porespace (to the limit where the expanding trapped air is in roughly at atmospheric pressure).

could you cure the resin at pressure? i've seen that done for resin castings. even a couple of atmospheres will reduce the bubbles significantly

 

[Cushing H.]

seen that done for resin castings. even a couple of atmospheres will reduce the bubbles signifi

Technically i suppose you could - but you would need to find a way to remove it from the pool of resin around it, all while maintaining pressure, before you heat it. If you release the pressure at all before curing the trapped air will expand and push resin out (it will “ooze out” of the outside of the block (god .. what an image...). Probably technically really hard to do. Good thought though!

 

[Rhinoknives1]

Technically i suppose you could - but you would need to find a way to remove it from the pool of resin around it, all while maintaining pressure, before you heat it. If you release the pressure at all before curing the trapped air will expand and push resin out (it will “ooze out” of the outside of the block (god .. what an image...). Probably technically really hard to do. Good thought though!

Crushing, I send my wood to K&G or WSSi because I get a batch or two maybe a year or two of Buckeye, Maple that I know benefit from this Process to be possibly Dyed and then Stabilized. I buy A few from others I know that send theirs to the same outfits and maybe trade a few of my Rhino fingers Skins for ——the scales........It’s not worth all of the hassle of playing with these chemicals, Dyes, buying a pump etc... I’m a one man band and don’t resale.. you have cleared up many of my thoughts & questions that I’ve wondered about the process and I thank you for your time & knowledge!

 

[Cushing H.]

. you have cleared up many of my thoughts & questions that I’ve wondered about the process and I thank you for your time & knowledge!

You are very welcome - im glad this helps!