Re-Fortifying Ancient Wood
I will be working the wood in its wet state, and hopefully getting it to dry enough to take up something which will saturate the cells and give the wood better structural integrity. I already have pentacryl, and PEG, and I normally use cyanoacrylate on some of the spalted wood.
I was wondering if there were any of the thin epoxies that might be right for this? Are they really good at penetrating, and how dry does the wood need to be? Any recommendations would be appreciated.
From contributor E:
The Smith and Company resin is pretty good stuff but most epoxies will give you some problems if it's still wet. An interesting strategy that I have seen used is to immerse the wood in some resin, weighted down if necessary, put under a strong vacuum (like 25" HG) in a vacuum bag or something similar. You then wait until it stops foaming and allow normal pressure back in and the resin will drive right through most porous woods.
From the original questioner:
To contributor E: I was already planning to use the vacuum. My pump usually draws 28" Hg.
From contributor S:
To treat the wood, put it in a reservoir in a vacuum chamber, with a line from outside going into the vacuum chamber, positioned to fill the reservoir. Put a valve in this liquid filling line. That connects to an outside reservoir of Clear Penetrating Epoxy Sealer
An oil-less rotary-vane vacuum pump that will pull 25" is adequate, although an oil-type pump can be used. The oil needs to be flushed and replaced more frequently due to water condensation.
Pull a vacuum on the wood piece to be impregnated. If it is wet, it will take longer to evaporate the water, as evaporation cools the remaining water in the wood, it gets colder, the water vapor pressure drops, and the remaining water evaporates more slowly. This can literally be freeze-drying.
Better for drying wood is to leave it in a convection-oven at 140 F or so, overnight, and weigh carefully with a gram scale until its weight loss has slowed down. This usually takes 24-48 hours. Then put it in the vacuum chamber, and pull a vacuum. The natural porosity of the wood will vent its trapped air in only a few hours typically.
Once the wood has out-gassed, valve off the vacuum pump line and valve on the liquid-filling line. The Clear Penetrating Epoxy Sealer will come in, driven by the external atmospheric pressure. It will splatter about quite a bit at first, so the interior reservoir should have high walls to contain the spray. Fill until the wood is immersed. (I forgot to mention earlier to put a lead weight or two on top of the wood so it does not float at this point), meaning entirely covered with the liquid.
Now valve off the liquid-filling line and valve on the external-air line, and bring the vacuum chamber up to atmospheric pressure. That being done, you have almost an entire atmosphere of pressure driving the liquid into the wood. Leave it immersed for about ten minutes, and you should see then that the liquid level is not dropping any more.
Take out the piece of impregnated wood and put it somewhere to dry out and cure and allow the solvents to diffuse out. This may take a week or so.
In most cases vacuum impregnation is not necessary, as the porosity of the wood and capillary forces will draw the clear Penetrating epoxy Sealer into the wood very nicely. Simple immersion of a weighted-down piece of wood in Clear Penetrating Epoxy Sealer, covered, for twenty minutes, is normally adequate and should be done first and the results evaluated.
I personally have used simple immersion to stabilize some six-million-year-old wood; it was a fossil fern trunk buried in mud for all that time, away from oxygen, and some was still wood whereas some other parts were mineralized and had actually grown fossil opal in layers around some of the growth rings.
From the original questioner:
To contributor S: It is close to what I am planning to do. After the wood is dry, I plan to put it into a bag, which, besides the evacuation line, will also have pick-up lines that lead to my mixing container of epoxy.
After drawing and holding the vacuum for a while, I will then open the flow lines and allow the epoxy to be drawn into the wood. I believe with this method, I can get by with less mixed volume of epoxy because the only place for the epoxy to go will be into the wood, and a thin bleeder fabric surrounding the wood. This is similar to a method being used to build boats lighter and stronger these days. Did you find it yourself, and where did it come from, and how big?
From contributor S:
To the original questioner: One of my customers dug it out of a mud bank where they allow tourists to dig for fossil opal. It has to be kept under water or the opal dehydrates and disintegrates, and the dry crumbly wood falls apart. It was about an inch around and a few inches long.
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