The contractor's recommendations strike me as pretty funny. The ratchet strap idea is especially mystifying.

Warpage probably isn't a big issue. I'd be more worried about cracking. With any such slice of a tree, radial cracking (from the center out to the bark) is almost impossible to prevent because the cellular structure of trees resists shrinkage along lines radiating from the center of the tree while allowing more shrinkage tangential to the annual rings. (Sorry for the jargon). Some woods are worse than others in this respect and, according to Hoadley's Understanding Wood, cottonwood is among the worst in this respect. In other words, your odds are not good. If the surfaces of this piece are left exposed to air, the cracking will start very quickly.

Polyethylene glycol, commonly known as PEG, is sometimes used to stabilize such chunks of wood. The wood is soaked in a solution of the stuff, which is absorbed and ultimately prevents the wood from shrinking so that cracking is prevented. I've never tried it, but I'm linking to a good resource. It looks as if you'd need to soak that chunk in a 50% solution for at least a couple of months. A search for PEG on that site will turn up more information.

Here is a link that might be useful: PEG primer on woodweb

Coincidentally I obtained a few like pieces of Cottonwood back in March and had them seasoning in my garage. By late summer they showed quite a bit of splitting and cracking but I kind of expected it. I was just going to use them as rustic seats so I wasn't that concerned, but I did experiment with some of the larger pieces. Some I sawed and planed (3 or 4 inches thick), and these seasoned fairly well. I turned a few pieces on a lathe and they also seasoned quite well. I should warn you though that it was fairly hard to plane and very difficult to sand - the grain fuzzed a lot and it was hard to get a smooth surface - this may have implications for your table top finishing.

I like to turn different woods I can pick up for nothing, and unfortunatley any thick piece of wood of most species has splitting and cracking problems. Just think of a big pile of firewood seasoning - all the cracks that develop in the ends of the wood as it dries. I think it's why sawmills cut up a log as quickly as possible. On woodturning sites they mention a product called anchorseal (which you apply like paint with a brush), which may be similar to or some derivative of the PEG the other poster mentioned. You can get it online, and I noticed they were even carrying it at a local lumberyard in my area. Woodturners coat the green pieces they turn with the stuff and it helps them season with less cracking - they do the whole piece I guess. In lumberyards they paint the ends of the boards to minimize edge splitting.

Since your cottonwood was probably sawed with a chainsaw (like mine were) you are going to have a tough time planing and smoothing out that surface for your table top. It did a number on my hand plane (which isn't really meant for end grain anyway). Hand sanding will take forever. It's a crude tool, but you might want to try a belt sander with an aggressive grit for smoothing your top (expect to go through a few belts). Your best hope for minimizing splitting is to keep it out of the sun in a temperate location. Put it on some sticks or a pallet and turn it occasionally so it doesn't mold too much. If you don't want to trust to luck use the PEG or anchorseal on it. Keep in mind that a thick piece of wood takes longer to season when you are air drying. I think I read somewhere that a 3 or 4 inch thick piece of oak might take 4 or 5 years to completely season. I doubt if you want to wait this long but I would wait at least a year. If you don't mind some imperfections I think it could be quite interesting. It's not very decay resistant so I would definitely use it in a sheltered location if you take a lot of trouble sanding the top smooth. Finish it with something if it will be exposed to the sun on a patio, even after it is seasoned direct sun will initiate cracking.

Danfurmanek, that is a nice link you found.

Anchorseal is NOT a substitute for PEG; it is simply a temporary topical sealer. Sawmills use it to buy time, saving logs from damage until they get around to sawing them into pieces, and also to prevent the ends of boards from drying faster than their middles, which would also cause cracking. Other people use it, as bhrost described, to slow the drying of smaller chunks of wood so that the drying occurs with minimal damage. This technique will not be very useful for a slice of a whole tree trunk; such a slice will crack when it shrinks, no matter how slowly that shrinkage happens. PEG helps by preventing shrinkage, not delaying it.

It gets pretty pricey to get enough PEG for a very large round.
The entire round must be submerged in the PEG/water solution, and the concentration of PEG monitored and adjusted for absorption and evaporation of water.
Simple plywood boxes with plastic liners work well.
Be sure you have a drain available if a leak occurs.

I was wondering what you ended up doing with your tree slice?
My husband has a section of a white oak tree trunk about 3-4 feet by 3-4 inches that we're hoping to turn into a table top. Any suggestions beyond these posts?

I used a bunch of White Oak slices for stepping stones in my garden. They have been there 3 years and still look nice. They were not treated in any way. The bark has fallen off but it just get mixed in with the surrounding dirt and mulch. My white oak slices are only about 2' in diameter. They do not get slippery when wet either.

I have a seasoned slice of a tree trunk about 36" around and 4-5" thick. My questions are:
1. What's the best way to sand a piece of wood like this? I don't want to ruin the grain of the wood.

2. Will a standard clear varnish/shellac work?

Grazie,
HenryS

you need to leave the log as a whole and let it cure ....then slice it otherwise if you slice it first it has room too expand while drying. if you leave it a log until done curing it wont expand because it dried as a tight piece of wood.

Should anyone consult this thread in the future, please ignore gabe huff's comment above; it is completely wrong. Wood does not cure well in log form, and it doesn't expand as it dries, either.

Here is the information about wood drying and shrinkage from USDA in the Wood Handbook.

Figure 3-3 is very good at showing how wood changes shape and size as it dries (and then continues changing forever as the moisture content varies with relative humidity).

Here is a link that might be useful: USDA Wood Handbook, Chapter 3

i'm pleased i found this forum.. i've been looking for some helpful tips and thankfully i believe i found some people who can possibly help me. my project: i have a 2' section of a cottonwood trunk about 5' wide that i want to turn into a table top as well. it has been sitting outside, here in ia since last summer. it has cracking, but i don't believe all the way through.
unfortunately, i have no experience with wood in this state. i've asked around and picked up on things such as cure time, and PEG... but basically as terms, and not as informative steps to proceed with. any help would be greatly appreciated.. as this is a project my grandfather and i have that may be his last.

Jason, I'm not sure PEG will be practical but you'll find detailed information in some of the links further up in this thread.

I was just presented with a 4" X 48" slice of a Pin Oak from my back yard. How fast do I have to start preserving it? Is PEG the best for Oak?

PEG us just about the only thing that will allow a slab cut from a tree to not split and check as it dries.

You need to start PEG treatment as quickly as you can, before significant drying occurs.

I have a 5 foot diameter piece of oak 3 inches thick soaking now.

I am trying to make clocks out of whole tree slabs. I see your discussion here and would like to ask: My pieces would be much smaller approx. 12 - 14 " diameter and approx 1/2" thick. I have looked into apoxy resin for wood, and see you are mentionin PEG. does any one know which I should use, or should i use both? How long would a piece that size have to soak in the PEG? I am looking to use cedar for its nice grain & softness, Am I correct in using a softer wood for better results of not splitting? I also would want to have a glossy finish on finished peice. In the end I need a finished product I know will not split. I have talked to a few mills & such and they are telling me that there isnt a way to cut a whole slab and have it not split and that to even kiln dry a piece that size would take like 3 months & probably loose the bark, yet I see many samples of what I'm trying to make for sale and I dont think they all used 100 year old wood thats completely air dried on its own. I would very much appreciate a response from someone who could help me. Thanks in advance :)

This may be too late after the post to get attention, but there IS an alternate way to avoid splitting and cracking without using polyvinyl glycol.

Make a straight saw cut from the outside to the center of the slice. Now shrinkage of the wood due to drying will normally be adjusted at this cut, widening it to a "V shape. 'the rest of the slice will be intact. I usually just finish up the slice when dry, using a belt sander followed by rotary sander to a smooth finish (hand sanding inside the V) then applying varnish or polyurethane coat.

If you insist on authenticity, then you may take a V-shaped cut from an adjacent slice, trim and glue it in to exactly fit the primary V. More trouble but unique result without poly glycol!

"If you insist on authenticity, then you may take a V-shaped cut from an adjacent slice, trim and glue it in to exactly fit the primary V. More trouble but unique result without poly glycol!"

And not likely to remain un-split when the humidity changes throughout the year.

PEG and PVA are not the same thing.