Veneering with Crotch Mahogany
Advice on veneering techniques that can improve the performance of crotch Mahogany veneer. January 14, 2013
About three years ago I had some veneer panels done with crotch mahogany, and I had it hot pressed to MDF substate. It has looked great up until recently, but now it is starting to get small raised places in it like it is going to crack. I do not know if it is drying out or what to put on it. I do not have a lot of experience with veneer and this is on some very high dollar cabinets. They have had some sun. Could someone please share some recommendations on what I need to do, or if there is anything I may put on them?
From contributor C:
That's what crotch mahogany does when pressed directly to a panel. We have been doing grand piano tops and components for years with it. There several things you need to do to prevent this. The material has to be treated for flexibility using GF-20 or similar. You should hot press the veneer to a poplar or similar cross band. You should use a Tego film adhesive or at least a Urea Resin adhesive, and it must be hot pressed. The 2-ply then can be pressed to a panel (with an equal backer).
After sanding you should glue size before finishing. In addition you need to watch the MC of the core and veneer prior to and after pressing. That usually will keep checking from happening, although sometimes it doesn't. As far as I know, there is not a permanent solution to fixing the panels you have except maybe an epoxy type finish. Most stock plywood houses do not follow the above so what you are getting is to be expected. Check with your supplier and see if they did any of the above. I'm not sure you would have any recourse.
From contributor O:
I am sure Contributor C抯 method of using crossbanding when lying is correct, however if it is of any use in discussing the flaw with your client I would. Note that if you look at the great 揂ge of Mahogany?masterpieces the wonderful carved cabinets with the beautiful panels of crotch mahogany are for the most part cracked and fissured. In antiques it is accepted as part of the charm of crotch mahogany.
From contributor C:
On the Tego film glue you need to hot press it at 275 degrees F and use at least 100 psi. It is important to go in the press with the veneer at high moisture content (some spray water just before pressing) as the high temp and long press time (five minutes) will turn your lovely veneer into a potato chip. Anyway, this takes a very strong press to get that much pressure and heat. A vacuum press is 15 psi at best.
From contributor A:
We use an Axlo Nobel pre-cat finish. Our piano mfg. customer uses a polyester finish and has no problems with checking. No matter what you do, if it is not cross banded, the core and veneer movement (dis-similar) will create checking again. If it's minor and you want to try, strip the old finish, re-sand, glue-size the veneer, sand very lightly, and re-finish. The epoxy would be any clear two part finishing epoxy. The problem is that it looks like epoxy unless you put it on light and then lacquer over it. You can get a finishing epoxy from U.S.Composites. Try it on a sample, it may eliminate your checking. We have had similar issues even with following the rules, but it's rare. Crotch cut wood is very hard and if it moves it cracks.