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Wood Stabalizer Question

Posted: Wed Sep 14, 2016 3:27 pm
by Iowa Big Tree Guy
Recently, the second largest remaining American elm in Iowa was cut after sustaining storm damage. It was a beautiful tree with a circumference of 16'1", a height of over 80' and a crown spread of 115'. Slices of the trunk were saved for the Iowa Arborist Association and for the Science Center of Iowa, where I work. I'm wondering if it would be best to use Polyethelyne Glycol (PEG) or Pentacryl/ Wood Juice to stabilize the wood.

In 1983 I salvaged a cross section from the state champion bitternut hickory that was cut after it lost a limb. I contacted several saw mills to see if they would be willing to give the section a precise, straight cut. They all turned me down because it was a city tree and there could be metal hidden within the wood. I ended up making a frame around the section that was laying flat. Then using a circular saw, I cut a 1/16 " swath at a time until I covered the whole surface of the 40" slice! I used PEG to stabilize the wood and it worked very well. The only problem with PEG is that it stays wet and some of the chemical will actually exude from the wood at times. This is part of the reason you are very limited with what you can use as a finish.

A few years ago, I used a product similar to Pentacryl called Wood Juice in an attempt to stabilize a couple of cross sections from the trunk of an Iowa white oak over 400 years old. Because the outside layer of the trunk was soft, I used product called Polycryl on the soft wood to try and firm it up. I didn't want the section to check during this process so I was also brushing Wood Juice on the rest of the slice at the same time which is not recommended. To ensure maximum penetration of the chemicals, I was applying the Wood Juice and Polycryl to both sides which meant constantly flipping the 6" thick by 45" cross sections!

I did this through the fall and winter before the slices were completely saturated. After about two years of slow drying the results were less than satisfactory. Both sections suffered considerable checking. One checked so severely I considered it unsuitable for display. Because one was slated for the Iowa DNR, I decided to cut the better section in two to get another slice. That proved to be a poor decision because even after two years of drying the wood was not yet dry. Cutting the better slice into two, made each slice thinner and more prone to checking. One of the newly cut sections actually separated into two pieces! I had envisioned what the finished slices would look like and they turned out so poorly, I lost all of my enthusiasm for the project.

If I had just submerged the sections would that have made a difference? The sections were wrapped in cardboard and left in an unheated building for drying. Unfortunately the were leaned against a south wall which probably fluctuated in temperature. Sudden changes in temperature are probably very bad for trying to stabilize drying wood. White oak is very dense, could that be part of the reason for the lack of success?

After the experience with the White oak, I'm leaning towards the PEG but I would appreciate comments from anyone who has had some experience in stabilizing large cross sections.


Re: Wood Stabalizer Question

Posted: Wed Sep 14, 2016 5:31 pm
by RayA

Two years ago we treated a 7" thick cookie of hemlock 42" in diameter with Pentacryl. The disc was from the New England champion hemlock, which came down during a winter storm. We wanted to preserve a cookie of it and display it in the visitors center of the state park in which it grew. We contacted Preservation Solutions, the maker of Pentacryl, for advice. They were very helpful and gave us exact directions on how to treat the disc. The center 10 or 12" of the disc was rotted, but most of the material was still there, though much of it was essentially like sawdust. We ended up diluting a gallon of white wood glue with water and flooding the rotted area with that. Once it hardened, we treated the rest of the cookie with Pentacryl. We placed the cookie on sticks over plastic sheet, and applied flooding coats on it, over a period of days, until the wood seemed to be saturated. Pentacryl will seep down into the wet wood and do the job; it should come out of the wood on the bottom side at some point. I think we did flip the cookie at least once to apply it to the bottom side as I recall, but that may not be necessary in all cases. The maker recommended covering both sides of the cookie with cardboard discs once it's saturated, to prevent rapid surface drying, and setting it aside to dry for several months. They said we could apply Lysol to the wood first to prevent mold; we didn't do that though.

We only covered the disc with plastic once it was saturated, and stored it outside out of direct sun. Once we judged the disc surface to be sufficiently dry, we brought it to a mill that had a huge capacity horizontal bandsaw (made by Woodmizer, but BIG!), and they took a thin slice off both top and bottom sides of the cookie, giving us a nicely smooth pair of parallel surfaces. We then sanded both sides with a belt sander, and applied a few coats of polyurethane varnish to both sides. It's been on display for two years, and came out great. A few shallow hairline surface cracks appeared, but no other defects at all. It worked beautifully. Other wood species may differ due to different porosities and densities.

My suggestion to you is to contact Preservation Solutions and talk with them. They will give you good advice based on your particular cookie. They also have online info, and a calculator to determine how much Pentacryl you'll need. Don't allow the cookie to dry out at all before being treated, or it will crack. Once dried, the Pentacryl treated wood is not wet like PEG treated wood. Most any finish can be applied over it. I highly recommend it, but do get advice from the maker for best results. They'll be helpful.

Good luck!


Re: Wood Stabalizer Question

Posted: Thu Sep 15, 2016 12:09 pm
by Don
Of course the desired end product matters! My friend wished to have workable wood after the preservation treatment, and he chose the PEG treatment. He had a dozen 4' cookies from the interface of black and english walnut grafts (trees bordered an agricultural area, and were taken out for more acreage...) He had members of his parish who were having to discard 500 gallon stainless steel tanks (vineyard) and managed to obtain several. As I recall, he submerged them for 6 months at a time, and turned them over for the second 6 months.
He really liked the treatment...left the wood, not so much moist, but, uhh, waxy? Once he had the shape he wanted, it was a burred straight edge that put on the final "finish"...none of his woodwork required ANY finish, and the grain was awesome. Water would run off of it like mercury...
His was a nearly industrial undertaking (in his garage!), I recall that the PEG came in about 1 foot cubes, and weighed more than steel.

Re: Wood Stabalizer Question

Posted: Sat Sep 17, 2016 3:15 pm
by Rand
I have a stupid question. You know how the center of cookies always split out at the pith, making a big crevasse in the middle? Obviously this has something to do with the wood drying, but I could never wrap my head around why the wood in the center of the cookie would shrink more than the wood on the outside (near the bark), causing the center of the cookie to separate from itself, leaving a void in the middle.

Re: Wood Stabalizer Question

Posted: Sat Sep 17, 2016 5:48 pm
by Don
Rand, not a stupid question at all ! I recall (some 40 plus years ago) such a question on my Wood Tech and Science class final exam. Technical answer involves a discussion of the various species of wood's tangential shrinkage ratio. Has to do with our nature (to have things flat and smooth and dry) and the tree's nature (to have things round and intact and moist)...any time we cut into wood, we're at odds with it until you get way out on a large diameter log and you cut perpendicular to the center. There you approach parallel annual rings (for example a 1" x 12" board cut from the outer third of a large diameter log (for extreme example, say 6 foot diameter)...there won't be as much of a tangential shrinkage ratio issue there. Any diversion from that simplistic example involves more internal stress to warp, crack, split, check, etc. That's why knots can often be a problem in lumber, where stability is important, hence knotty lumber is considered to be of poorer grade.
Probable haven't helped much, but want you to know it's a good question!