resin and slabs and wood movement

[Mike Barney Sr]

I looked over the topics and could not figure out which to post this in. I figure finishing was probably the best.

A coworker who also has a woodshop completed his first project using an ash slab and resin to make a workbench for his wife. The top is what they refer to as a "river" table, where the slab is ripped an the live edges are placed side by side and the gap is filled with clear or colored resin to look like a river. They look great but my question is about differing movement. The wood at 2" is quite wet inside and this moisture will want to migrate out in the course of time. I have watched many projects of this type on youtube and facebook and I never see them finishing the underside. I understand the resin coating is probably the best seal one can have on wood as far as a moisture barrier but is the bottom is not sealed as well as the top you will have warping. Even if the bottom is finished temperature will play a role in creating dimensional changes. Also will there be unevenness in the thickness especially if the resin is next to a section of quarter sawn grain.

I have not been able to find any reports of these projects years after their completion, most likely because this is a relatively new fad. If there is anyone out there who does have any info on the longevity of this process please reply. I am quite curious

[Jamie Buxton]

If your friend used green wood for his table top, it is going to dry and shrink. It will do this regardless of how he finishes it. The biggest effect will be that the overall width of the top will get smaller. If he has firmly fastened the top to parts that will not get smaller in the same way, the top will likely split. I'd be concerned about resin bonding well to wet wood, and wouldn't be surprised to see the resin/wood interfaces to pull apart. A smaller likely effect is that the top will cup. It will be concave toward the bark. Making anything more than rustic furniture with green wood is asking for trouble.

[Mike Barney Sr]

He used kiln dried lumber of course. But even with kiln dried lumber the inside is still considerably higher in moisture than the outside. I have resawn thick kiln dried lumber many times and I always count on it to cup towards the resaw cut. And it does. Even on some 25 year old well stored lumber I once had. The inside of the board always is wetter. And this is why I question using a dimensionally stable product such as resin with a product that is not without making concessions for this. Wood moves. Period. (see my signature)

[Jim Becker]

The "river" in the middle is more or less not material because almost all movement is going to be in the two surrounding boards. That movement is going to be across the grain. (to/from the edges) Unless the finish on the wood is so thick that it really restricts things (doubtful) I don't think there's going to be a major problem if the lumber was within reasonable MC when the piece was built.