Q: I have made some cutting boards that after several uses are starting to develop cracks in the ends at the glue joints. What advice can you give me to stop this?
A: I think you first have to understand what is happening. When a board is washed, the end grain will pick up moisture and the fibers will swell. However, the rest of the board, because it does not pick up moisture as fast as the end grain, will not swell as much. In other words, the rest of the board stops the end grain swelling. As a result, with this end swelling, compression forces develop that squeeze the cells at the end of the board. Some of this compression is large enough that it is permanent. Now when the cutting board subsequently dries out, the cells at the ends will shrink. However, the end is now a little smaller (due to the permanent compression) and so when the end cells shrink, they create tension that can be large enough so that the cracks are created in the ends. With tension forces building due to shrinkage, the weakest spot will fail. As all glue joints have the potential to be stronger than the wood itself, the failure should be in the wood (unless the glue joint is not up to snuff).
If you see open glue joints, go back to your gluing process to make sure that it is close to perfect. Glued edges should be freshly prepared (within an hour), flat, true and so on. Use a "waterproof" adhesive, such as Titebond II, which is crosslinking. Then use a finishing system that is approved for cutting boards that also waterproofs the end grain as much as possible. Finally, put a note on the board that suggests that the boards not be soaked or put into a dishwasher.
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