A client asked for a desk top that was reversible, with wood on one side and leather on the opposite side, so that it could be switched from one to the other. I used 1/8 inch sapele on one side, leather on the opposite, with 1/4 inch MDF for a core. I used Titebond III on both surfaces, put it in the vacuum press for 6 hours. It worked fine until the room it was in heated up with the sun streaming onto the desk. Like a potato chip! I’m going to re-do it with 1/8 sapele on both surfaces. Should I use PPR adhesive (which I already have)? Unibond 800 (which I will have to order)? Should I use Baltic birch instead of MDF? Or, I can use 3/8 inch substrate with 1/8 sapele veneer on only one side. I will glue the panel to the 3/4 inch Baltic birch desktop this time, as it no longer needs to be reversible. The panel needs to be 1/2 inch thick to fit.

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Sapele both sides. MDF is fine as a substrate. The choice of glue was not the issue in this case it was the unbalanced glue-up. The sapele dried which put tension on one face. The leather has no resistance to the warping forces. 1/8" veneer will impart a fair amount of tension on the panel especially when it is so thin.
You could probably get away with sapele on one side again because you are gluing it onto the table but how good will that gluing be in an already assembled desk? Better safe than sorry.

Thank you Tom. I will go with MDF and veneer both sides. And my fingers crossed.

It's the glue go to these guys they have the right glue
https://www.veneersupplies.com/categories/Veneering__Supplies/Veneer__Glue/
Also I know a lot of people glue veneer to MDF for such a small piece use Baltic then you don't have to worry about balance.

I also would like confirm that the construction and glue choice were the problem. You should have better luck with thinner veneer, balanced panel, and a ridged glue line (for something this small a polyurethane glue would be handy).

I would not use TB III with 1/8" veneer, balanced or not. I also see no reason to use 1/8" thick veneer. If you need 1/2" final thickness then use 3/8" MDF or BB and glue 1/16" thick veneer on both sides, preferably with PRG or Unibond 800, or TB Original or TB II. If you can't get 3/8" then sand down 1/2" MDF and use extra glue to satisfy its thirstiness.

Above all, do not use Better Bond with any shop sawn veneer. Learned that one the hard way.

John

What Tom said. The problem is the unbalanced panel. I would not use T3 for veneer as it is not a very rigid glueline. If you want to use a one part water base glue Titebond Extend is decent. PPR or epoxy are more rigid. 1/8" is the absolute maximum thickness I would use and 3/32" or less is preferable, on both sides of the panel.

1/8" is not veneer, its wood just thin, then when you add the thin MDF its not good, doing both sides would be a start it still could warp again tough I would use 1/42 veneer and a thicker core