Does a well secured panel need to be veneered on both sides?

[David Kuzdrall]

I am building a modern looking book case out of some quartersawn, spalted sycamore lumber. The lumber was 5/4 so I resawed 1/4" off to use as the back leaving the rest for the case and shelves. By the time I surface that 1/4" stock it will likely be 3/16 or less leaving me to believe that I might as well get it converted to veneers.


my overall plan is to keep the case joinery clean (I usually just dovetail everything and show off the joinery) so I am going to go with miters reinforced with a hidden spline running the depth of the case. If i do this the joints will not have and long grain to bond to but plenty of integrity to support a load, so I need to address racking. If I veneer this lumber to some ply, then I can nail it to the back and address the racking, the issue is that I only have enough lumber to veneer one side of the ply.


the size of the ply back will be ~47" x 34" and have ample areas within that space to nail it to the back of shelves and vertical dividers (I can basically nail it every 9-13"). With that amount of fastening points, if I use 3/8 ply, will I need to also veneer the back?


thx

[Keith Bohn]

Are you saying you'll have 3/16" solid wood applied to a substrate? If yes, you'll probably have worser problems with the face splitting. For all intents and purposes it's not veneer, it's still solid wood.

[Mike Henderson]

I've never worked with 3/16" "veneer" so I can't give you a definite answer. The thing that causes bowing in a panel is uneven absorption of moisture, even in ply or MDF. The initial bowing is usually seen right after you do the glue up because most of us use water based glue (when you only glue one side).

Often, if you're willing to wait long enough until the moisture equalizes, the panel will straighten out.

To avoid (or minimize) this, most people glue up both sides of a panel at the same time. That way, you introduce moisture on both sides and you encounter much less bowing.

If I was putting in a back to a carcasses, I'd run a groove around the inside of the carcasses and then install the back panel when you glue the carcasses together. That hides the raw edge of the back panel and captures the panel pretty well to prevent racking (if the panel is a tight fit in the grooves).

When you glue up the panel, you can use some regular (1/42") veneer on the back of the panel. You're probably going to need a bag to glue it (unless it's a really small panel) and some glue that gives you a long open time.

If you decide to only veneer one side, and you have time to let the panel equalize, putting it into a groove will keep it pretty straight, especially if you finish the back of the panel well.

Good luck,

Mike

[If you don't have room for a groove, I'd do a rabbet around the back of the carcasses and inset the panel into that rabbet. That will hide the raw edges of the back.]

[David Kuzdrall]

Are you saying you'll have 3/16" solid wood applied to a substrate? If yes, you'll probably have worser problems with the face splitting. For all intents and purposes it's not veneer, it's still solid wood.

No. 3/16" is too thin for a solid back so I will either have it sliced or sanded down (or both) into veneers 1/16" or less.

[Jamie Buxton]

No. 3/16" is too thin for a solid back so I will either have it sliced or sanded down (or both) into veneers 1/16" or less.

So use your show veneer on the visible face of the back, and use some other species for the non-visible face. Or use a lower grade of the same species -- for instance non-spalted sycamore. Either of those is perfectly legit.

[David Kuzdrall]

I've never worked with 3/16" "veneer" so I can't give you a definite answer. The thing that causes bowing in a panel is uneven absorption of moisture, even in ply or MDF. The initial bowing is usually seen right after you do the glue up because most of us use water based glue (when you only glue one side).

Often, if you're willing to wait long enough until the moisture equalizes, the panel will straighten out.

To avoid (or minimize) this, most people glue up both sides of a panel at the same time. That way, you introduce moisture on both sides and you encounter much less bowing.

If I was putting in a back to a carcasses, I'd run a groove around the inside of the carcasses and then install the back panel when you glue the carcasses together. That hides the raw edge of the back panel and captures the panel pretty well to prevent racking (if the panel is a tight fit in the grooves).

When you glue up the panel, you can use some regular (1/42") veneer on the back of the panel. You're probably going to need a bag to glue it (unless it's a really small panel) and some glue that gives you a long open time.

If you decide to only veneer one side, and you have time to let the panel equalize, putting it into a groove will keep it pretty straight, especially if you finish the back of the panel well.

Good luck,

Mike

[If you don't have room for a groove, I'd do a rabbet around the back of the carcasses and inset the panel into that rabbet. That will hide the raw edges of the back.]

I will be using unibond800 for this project....so moisture absorption through via glue would be a non issue. I have rabbeted the back, so it will be clean looking and I may even get lucky and yield more sanded veneer than I thought so maybe I will be able to veneer the back with the same species.

it would be interesting to conduct or review an experiment to see just how much force is applied to a substrate based on veneer species / cut type / thickness and then see how well a few different substrates resist that force...

thx

[David Kumm]

For what it is worth, I glued 1/8-3/16 walnut to 1/2" ply for 8" baseboards a hundred years ago and they are all still straight. In some cases the veneer is from a more stable species than the plys which reduces the risk. I'm looking at a 4'x4' ply with african mahogany veneered on one side and it has also stayed flat. Not recommending but that has been my experience. If I'm doing cabinets with a side showing and no panel to pretty it up I will often veneer just the outside because ply looks like ply when finished. Dave

I should add that the larger the panel the thinner I will make the veneer. 1/16 -3/16 depending on how large or how secured. A cabinet side doesn't have a lot of room to move but 1/16-3/32 seems to work best. When it gets sanded down it's a little less. Dave

[Loren Woirhaye]

You can veneer solid wood veneers over solid wood substrate with the grain running the same way. If the expansion characteristics of the woods are similar, the panel will function a lot like a solid board.

I'd look at laminating the 3/16" stock to 1/2" backer boards or something. Seems like the easy way to go about it to me. I don't see an advantage in having 1/8" removed from from veneer stock.

[Peter Quinn]

I've glued a lot of 3/16" veneers to 5/8" Baltic birch for flooring at work, single sided, it never ever stays flat. Sometimes it comes out of the press flat but its a short lived effect. For "engineered" flooring its hardly a problem, it gets glued down and nailed in most cases, and it flexes to sit flat over its length. But I wouldn't trust this approach for a panel on a case, maybe the case keeps it squared up, maybe the case racks? I prefer a little more surety in my technique. I'd buy or make some backer veneer, I'd get that sycamore a lot thinner than 3/16". I like the veneer on solid approach, or even a lumber core glue up, its a lot more work but adds great strength, and those do tend to stay flat.