Replies

1. 
   EarlKelly | Feb 07, 2006 06:50am | #1

   The Key, is to know when, you can leave off the backside veneer. If you leave it off on the wrong piece, you'll get a warped panel. It's not so much the veneer, as the glue that pulls the panel. And if your considering not veneering the backside of even 3/4" plywood, a 2'x4' panel can warp enough to be easily seen.

   Furniture...the Art of a FurnitureMaker
2. 
   ring | Feb 07, 2006 09:26am | #2

   Dave,

   The key difference is that in adding veneer or laminate to one side of the sheet, you are adding a material (and its adhesive) which have totally different expansion and contraction coefficients than the underlying material.  It is this that needs to be "balanced".  You correctly note that you can glue wood to itself face-to-face with no problem, but if you do it with 2 different species you will get an interesting demonstration of the forces at work.  As far as adding an "extra" layer of veneer to 3/4" ply, look at it this way -  the industry has understood long ago that sheets need to be made up in a symmetrical way for them to be stable.  They are not idiots.  Maybe in some cases the panel will resist bending, but it certainly is under stress.  Suppose you knew that in 50% of your panels they would bend - would you glue them all symmetrically or throw 50% in the trash bin?

   DR

    

3. 
   RMillard | Feb 07, 2006 03:08pm | #3

   LD,

    

   You are correct, it is not necessary under all circumstances. I often veneer drawer fronts with no veneer on the back side. I've found as long as the front is less than 6"-7" wide there is a not problem veneering one side. ( I use a mahogany, cherry, or poplar as a substrate). Along the same line, I have veneered a many card table aprons on just one side with no ill effects. Tall case clock hood doors are another example were veneering one side is acceptable.

   Having said that, there are many more times where veneering both sides is absolutely necessary. I once thought I could veneer just one side of a prospect door in a Butler's Desk, since the door was quite small. I was very wrong, that door bowed at least 3/16" in the center of its 6" width. I hammer veneer, and I've found that I must quickly get the veneer on both sides, and then go back and make sure there are no bubbles or other problems, as the veneer starts to distort the substrate very quickly. Once the glue has set, not amount of clamping, coaxing, or cussing will ever bring it back to flat.

   When gluing two boards together face to you should take into account the growth rings. One school of thought is to have the rings oppose one another, but I'd prefer having them concentric. Plus with solid wood, you can plane out some distortion, which is not an option with thin veneer.

   On your example of veneering one side of a piece of 3/4" plywood, depending on the size it could be done, but a large panel, say more than 3' square could easily be distorted ( I'm guessing on the size, but I have no doubt the veneer would distort the ply)

   Cutting a thin piece from the face of a board often results in some cupping due to changing the moisture equilibrium, but this could be overcome by the glue bond, yet in a wide board, you'd be asking for trouble if you did not do the same thing to the other side. Here again if your off cut piece were thick enough you'd have some room to plane it flat.

   Rob Millard

   
   

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   Edited 2/7/2006 10:14 am ET by RMillard

4. 
   RickL | Feb 07, 2006 03:24pm | #4

   "All knowledge is gained through experience. Yours or others. Others is cheaper! "

   So why not do some reading as the subject goes back to the Egyptians?  Plenty of documented information on the subject so why ask the question? 

   Gluing to boards face to face is a different matter than gluing veneer to a face.

    The glue one uses  has an effect. A water based glue adds moisture so adding water to one side will certainly make a difference.

    

1. 
   LD | Feb 07, 2006 04:03pm | #5

   SO WHY DO YOU THINK I POSED THE QUESTION?

   Edited 2/7/2006 8:11 am ET by LD

5. 
   LD | Feb 07, 2006 04:17pm | #6

   Thanks for the responses. Most of the veneering I have done have been on small box tops and drawer fronts. I have always veneered both sides because of the potential problems pointed out in this discussion. It just didn't seem logical for this rule to apply in all cases.

   I usually use urethane glue in veneering. Could the use of this non water based glue change anything?

6. 
   joinerswork | Feb 07, 2006 05:33pm | #7

   LD,

   As Rob has pointed out, there are times where you can get by without gluing a balancing veneer on the backside of a panel.  To his examples, I'd add veneering the panels for a cabinet door.  I'll also point out that it makes a difference which way you run the grain of your veneer, as to whether you will likely have problems later on.  Your example of ripping a layer off the face of a board and gluing it back on, is similar to gluing a veneer long grain to a long grain substrate, like the clock door that Rob mentioned. Not usually gonna give you trouble, especially if the species is the same. You will more than likely have problems if you turn the grain direction 90* to that of the substrate.  Note too, that most of the examples Rob gave, the table aprons  and drawer fronts, like the door panels I mentioned, are restrained from warping, by being tenoned, or dovetailed, or captured in a frame.

   An easy place to see the results of unbalanced veneering is to look at period chippendale mirrors.  The top and bottom scrollboards are almost always warped to some degree, depending on how well the applied battens on the backsides have held up.  Card table folding tops are another example.  If veneered on one side, and not balanced, they usually will curl over time. 

   Generally too, the thicker the substrate, greater its ability to withstand the stresses introduced by veneering, and subsequent changes in moisture.

   Regards,

   Ray Pine