Stabilizing Wood with Polyethylene Glycol
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Advice and explanations about using PEG to prevent shrinkage and cracking in heavy wood disks being dried for a specialty application. July 15, 2014
Question (WOODWEB Member) :
I have many large four inch thick round slabs or cookies to soak to prevent them from cracking. I have a 1200 gallon poly tank to soak them in. I don't want to spend $15-$20,000 thousand dollars on Pentacryl. What else can I use that is more cost effective that will produce the same results? Ethlene glycol will discolor the wood after the wood dries. Not sure about Butyl alcohol. Are there any proven ideas?
Forum Responses
(Sawing and Drying Forum)
From Gene Wengert, forum technical advisor:
We use poly ethylene glycol 300, not ethylene glycol - big difference. If you use it, put the discs in a bag and fill the bag so you do not need a full tub of PEG. It only works well on permeable species. Alcohol might be worth a try, but I suggest trying it on a test pieces first.
From contributor S:
Where do you get PEG, and roughly what is the cost?
From Gene Wengert, forum technical advisor:
One source is Rockler Woodworking.
From the original questioner:
I checked on the cost of polyethylene glycol 300 and it is more costly than Pentacryl. I need multiple 55 gallon drums at a time. I am seeking a source or a cost effective means to soak and cure the slabs on a very large scale.
Gene, where am I going to find a plastic bag that won't leak and can fit a 5 foot diameter slab? Remember I want to completely submerge and soak each piece for ten days and process many pieces at a time in the same tank.
From Contributor N:
Just to share a bit of my research: I'm doing big carvings of, for now, poplar. I've become focused on polyethylene glycol 1000, mentioned positively by many for stabilization wood for turning projects. (Pentacryl has only recently come onto my radar but your problems with cost seem similar to mine with PEG.) My carvings will not fit within the 4’ max depth that is recommended but I'm moving ahead anyway. I'm currently carving an experimenting piece which I'm keeping immersed in water while not working on it, as an uneven drying process seems to be the main culprit. I plan, once this pieces approached it's final dimensions, is to trying soaking in a 50% solution of heated PEG (the ideal is apparently 140º) for a few weeks in an 8' watering trough I got through Tractor Supply. (They have some pretty large circular troughs, too, if this factor is still in the planning stage.) As for me, time will tell.
From the original questioner:
I can relate to your carving project using Poplar. Your idea of keeping the wood immersed in water is a good and reasonable one as you progress with your carving. Are the round tubs from Tractor Supply plastic or metal? How are you heating the solution to 140 degrees? What are your costs of the Poly Ethylene Glycol 1000?
From contributor K:
You don't need to immerse it, just spray it and then cover it with plastic sheeting or a cloth cover when you want to start a slow drying. The immersion will just add a lot of free water which will have to come out before you start losing bound water. I have managed to reduce a lot of checking by drilling the largest hole up the pith from the bottom that I can manage. This can be achieved by going with progressively larger bits and then adding extensions as they get deeper. Instead of trying to use chemicals I try to control the rate of drying. The sapwood of almost everything will dry faster than heartwood so sealing it while leaving the heartwood unsealed, then up on stickers inside a cardboard box inside another larger box should slow down the surface drying to a rate as slow as the moisture from inside can make it to the surface. I love carving green wood but patience in drying is the key. For sculpting you are much better off starting with a tree large enough to work with one side, leaving the pith out of the work. As for using those giant cookies I would plunge cut the pith out of a few with the chainsaw and then just plan on going back in the end with something creative.
From Gene Wengert, forum technical advisor:
Actually, the PEG replaces some of the water, so the amount of bound water is lessened with PEG treatment. I worked with PEG treatments over 45 years ago at the US FPL where it was developed. Note that the developers of using PEG 300 and PEG 1000 prefer 300 as it works just as well and is less expensive. In order to get the wood into the wood core region, there must be a supply of PEG at the surface so it will continue to diffuse inward. Hence, soaking is preferred. Check the SG frequently, so you know when to add more PEG as it is absorbed by the wood. They tried a surface coating of PEG and found it to be ineffective.
To lessen the amount needed for treating a single item, the plastic bag approach (you can get bags at least 4' x 4' x 12') works. For lots of items, the vat is more reasonable. Note that for any chemical to get into the wood, the wood must be permeable. Are you treating aspen poplar or tulip poplar?
From Contributor N:
Useful info as this is all going where I've never gone before, these ideas will be incorporated into my continuing experiments. The troughs I mentioned are galvanized with zinc coating. This will keep the PEG from turning dark and changing the wood color (theoretically). Also at Tractor Supply I found a water heating wand. I haven't used it yet and it may take more than one. I'm still trying to find the best price but Rockler has is in 10 lb. containers.
