I need to find a way to solve this problem. I have designed and built a custom bar for a client with the top made from IPE wood. I am getting some slight convex cupping of some of the individual boards where they were initially a flat, smooth surface. The link below shows some photos of the problem and construction details. Needless to say I did a lot of research before, during and since starting this project. The design alone was about 1-1/2 yrs. My inclination is to let it settle in its new home and then sand and refinish. Would the problem recur? How long would it take to completely settle? Is there another solution? I don’t have the option to remake it. Has anyone experienced and fixed a similar problem?
Related Web Page: Photos of Problem and Building Specifics
Your biggest mistake is treating this solid wood top as if it was a veneer. The reason to cut veneer thin and glue it to a stable substrate is to stop it from moving with shifts in relative humidity. If they are not thin, less than 1/16", the wood has too much structural integrity for the glue to be able to hold it. When it is this thick, if it doesn't break your glue line, it will tear chips off of the face of the wood, and fail anyway. You can not stop solid wood from moving. You need to learn to plan for it to move, or learn to veneer with the thin stuff. Both are good options, but not both at the same time.
Your project is just beginning to self destruct. My best advice to you now is to look at that last year of planning and research with a bit of skepticism, and see what you can learn from your mistakes now. If you had not glued it to the p/w substrate, the outer band would have been a mistake also for the solid wood option, but it would have been fine for real veneer over a stable substrate. If you believe that only solid wood is the real thing, you should have milled either T-slots or dovetail ways in the bottom and waxed the parts so they could move without warping or binding. Those parts could be connected to the carcass, while the top moves freely.
When I am teaching, I always tell my students that you can learn more from your mistakes than from accidentally getting things right without understanding why. Of course it is unfortunate to have to remake expensive parts. I hope my assessment is wrong, but I suspect it is going to get worse.
As for your second question, no - as of today there is no cracking at any seam at all. What you are detecting is something that you can feel as you rub your hand across the surface. The finish seems to be compressing and rising very slightly at the joints. I appreciate your candor in assessing a worst case scenario that may be imminent, as well as the very good advice that you offer.
As I began to notice the negative changes I began to call some of the Ipe yards and product manufacturers that are located around the country to ask for opinions and advice. The consensus was to leave it alone, wait and it would probably settle. I came to the knowledge bases and forums in case their optimism was wrong so that I might possibly come up with a positive pro-active solution. Worst case scenario is also good.
Since you do not address removing the finish on top to let it settle, as one of the Ipe guys suggested, what about removing as much ply from beneath in areas that will not show? I stress again that what I am looking for are solutions and alternatives to failure if possible.
I suspect that you used a lot of glue under there thinking it would need a lot to compensate for any imperfections. I know a fellow who made a mistake like yours. He was sure he had some faulty glue, and after talking to the glue hotline, he took his vast knowledge of glue, and added a powder glue to his Titebond to improve it, then made another top using the same method, only to have it fail.
Remember the two rules of woodworking:
1. Wood will always move in relation to any humidity/moisture changes, period.
2. Woodworkers will all disagree on how wood behaves in certain circumstances, when subjected to moisture and humidity changes.
If the piece has been in service for a while (more than a year) without the problem getting worse in a stabilized humidity environment, and you can count on the humidity remaining stable forever, you might get away with sanding and refinishing. That is a lot to ask. One possible solution might be to run the top through a wide belt sander to reduce the top veneer to an appropriate thickness and remove the bottom veneer, and immediately replace the bottom veneer with an equal thickness of Ipe as is left on the top. You would have to redo the edgebanding or add a separate apron to conceal the lights, and given that the core is plywood of almost surely varying thickness, the prospect of coming out with a perfectly balanced panel is doubtful. It might be a satisfactory and less expensive solution than starting from scratch.
As far as mitigating,is there any chance you can get away from a gloss finish? You could either rub to a satin finish or sand and strip back and use an oil finish. This probably won't do anything about the root cause (except for an oil – this might allow the top to breathe) but at least lighting would not highlight the problem.
Comment from contributor J:
If you decide to redo the top completely, I have to agree with the others suggesting you re-saw the IPE and apply it as a veneer. If you decide to go this route, it would be wise for you to use either Unibond 800 or an epoxy type glue to attach the veneer. These types of glues are appropriate for veneering. Also, keep in mind that one of the cardinal rules in veneering is to apply a like hardness and thickness veneer to the other side of the ply or MDF. You must have a balance of pressure on both sides to achieve a proper sandwich that will stay flat. If you apply veneer to one side only, it will cup and twist.
As to thickness, I think you could put on a 3/32 inch veneer and then sand it to around 1/16" finished. By doing this the veneer will still take a beautiful finish and also be thin enough to withstand years of use. Gluing the thick (5/8") IPE to a ply backing with Titebond will always cause any board to cup. Titebond and other glues of this type are not good for veneering as they move too much and will eventually lead to other problems such as the joints opening as the veneer shrinks and expands. You might want to look into the archives at this forum about veneering if you decide to pursue this route.