Learning the hard way - veneering mistake

[Alex Berkovsky]

I veneered a piece of plywood (63x17) for a dresser top on one side only. It looks like the plywood has bowed due to the fact that only one side was veneered. I placed some heavy weights on top of the plywood hoping that it will flatten under load - not sure if this method will work though. If I veneer the opposite side now with some cheap veneer, will it flatten the plywood?

[John Huber]

I made the same mistake. Even after veneering the second side, the plywood substrate still was bowed. Maybe the wood took a set.

You might consider this: veneer the second side; then laminate the sandwich to a thicker, stiffer backing panel. Maybe even make some cauls with bowed edges to bias the new composite opposite to the offending bowing.

[Cliff Rohrabacher]

you might try to spritz the reverse side with water and see if it returns.

[Alex Berkovsky]

you might try to spritz the reverse side with water and see if it returns.Cliff,
Once I spritz (or is shpritz :D ) the opposite side, do I just drop a few 50 lbs weights on top of it or maybe clamp it down?

[Carl Eyman]

If you are going to spritz with water, you should do the concave side, but if that is the veneered side, I'd not do so. I'd consider applying heat to the convex side to try to shrink it. Then when the piece is straigt veneer the off side. I'd most certainly not veneer it while bowed - either way.

[Joe Jensen]

I don't know why, but veneered panels almost always do this if only veneered on one side. The weaker the substrate the more the warp. I always veneer both sides. I've found that I can't wait more than an hour or so to do the second side. I think that as the glue dries, the veneer dries and shrinks, pulling on the substrate. I now always put laminate on both sides for the same reason.

[Rob Millard]

Alex,
Unfortunately it is too late to reverse the cupping by veneering the other side. What you can do, is kerf the underside, to relieve the stress, much like what is done with door jambs and flooring.
Rob Millard

[Dennis Peacock]

Man....that stinks...but it happens to many of us at some time or other. :( :(
With any substrate that you're going to veneer? Please veneer the opposite side of your "background" to better prevent/reduce these warp tendencies.

[Steve Wargo]

Carl and Rob have the right idea. If you can get the board flat, the try to revener it while it's flat. Also, you may want to put a heating blanket on top of the bag to help the glue cure faster once the piece is flat. The saw kerf method will work as well. Good luck. Too bad about the mistake, but it's one I've made before as well.

[Alex Berkovsky]

If you are going to spritz with water, you should do the concave side, but if that is the veneered side, I'd not do so. I'd consider applying heat to the convex side to try to shrink it. Then when the piece is straight veneer the off side. I'd most certainly not veneer it while bowed - either way.The concave side is the non-veneered side. Once the concave side is moistened, do I apply weight to the convex side (the veneered side)?


Alex,
Unfortunately it is too late to reverse the cupping by veneering the other side. What you can do, is kerf the underside, to relieve the stress, much like what is done with door jambs and flooring. Rob,
I am not sure what is done with floors and jambs... is it similar to making kerf cuts when bending plywood? If the ply substrate is 3/4", how deep should the cuts be and how far apart?
I will take some pictures tonight to show the project and see if other suggestions can be offered. You know what they say... a picture is worth a thousand words.

[Mike Henderson]

I veneered a piece of plywood (63x17) for a dresser top on one side only. It looks like the plywood has bowed due to the fact that only one side was veneered. I placed some heavy weights on top of the plywood hoping that it will flatten under load - not sure if this method will work though. If I veneer the opposite side now with some cheap veneer, will it flatten the plywood?
Alex - If you don't mind, could I ask a few questions?

1. What glue did you use to attach the veneer?

2. How thick is the substrate? I'm sort of assuming that it's 3/4".

3. How long was it between the time you veneered the plywood and when you noticed the warp?

4. Do you have the top attached or is it still loose?

5. If it's not attached, have you tried heating the panel, perhaps by putting it in an electric blanket, to make sure that you've driven out all the moisture from the glue?

Mike

[Tim Sproul]

It isn't a problem inherent with the veneer on only one side. Really, the problem is adding an extra layer of adhesive to only one side. Nearly all adhesives will change in volume as they cure (generally shrinking rather than expanding)....and hence have a bit of tension in the adhesive once cured. This tension tries to pull into the middle of the panel since the adhesive want s to shrink....use and adhesive that wants to expand and the veneered side will crown rather than cup.

The adhesive causing warp is why plywood has an odd number of layers of wood veneer (veneer core, obviously).....but and EVEN number of layers of adhesive. If the wood was the culprit for causing warp and not the adhesive, you'd balance the layers of wood veneer core and not worry about balancing the layers of adhesive.

[Rob Millard]

Alex,
The kerfs are similar to what is done to bend stock. In this case the kerfs would remove the tension so the piece could lay flat. It would be hard to say how far apart and how deep the kerfs should be. My guess is that you’d only need a few ( perhaps 4 kerfs) down the middle of the top and just over half the thickness of the top .
Rob Millard

[Alex Berkovsky]

Alex - If you don't mind, could I ask a few questions?

1. What glue did you use to attach the veneer?
White carpenters glue

2. How thick is the substrate? I'm sort of assuming that it's 3/4".
3/4" plywood

3. How long was it between the time you veneered the plywood and when you noticed the warp?
I didn't look at it for a long time and don't want to guess when the warp occured.

4. Do you have the top attached or is it still loose?
Still loose.

5. If it's not attached, have you tried heating the panel, perhaps by putting it in an electric blanket, to make sure that you've driven out all the moisture from the glue?
I don't have an electric blanket and would guess that the glue has dried by now. It's been about 3 weeks since I veneered it.

Here's what I have to deal with... I have to glue the mitered molding all around the veneered plywood which is warped. I then have to glue the top to the dresser.

http://i73.photobucket.com/albums/i232/jarhead8286/Woodworking/th_Dresser-front.jpg (http://i73.photobucket.com/albums/i232/jarhead8286/Woodworking/Dresser-front.jpg)

This picture may give you an idea how much the plywood has warped:
http://i73.photobucket.com/albums/i232/jarhead8286/Woodworking/th_Dresser-side.jpg (http://i73.photobucket.com/albums/i232/jarhead8286/Woodworking/Dresser-side.jpg)

[Eric Derry]

Why not attach the top to the dresser carcass, it should be substantial enough to pull the top flat and then apply your edge banding?

[Alex Berkovsky]

Why not attach the top to the dresser carcass, it should be substantial enough to pull the top flat and then apply your edge banding?I was thinking about that, but am afraid that I may not be able to line everything up.

Welcome to the creek, Eric.

[Greg Funk]

Alex,

It seems odd that the board warped away from the veneer. This means the veneer expanded rather than shrank. Maybe it will shrink back in a few days. You should be able to dry it out and cause the veneer to shrink enough to straighten out the panel. Is it in a warm dry area?

Greg

[Mike Henderson]

I see your problem. Even if you kerf it as Rob suggested, you need a way to hold it flat while you attach the edge molding. You could kerf it and then screw some temporary cauls to the bottom to get it straight, then put your molding on. When you have everything "finished" remove the cauls and screw it to the carcass to hold it in place.

If it was mine and I had more matching veneer, I'd do it over with veneer on the bottom.

Mike

[Alex Berkovsky]

Alex,

It seems odd that the board warped away from the veneer. This means the veneer expanded rather than shrank. Maybe it will shrink back in a few days. You should be able to dry it out and cause the veneer to shrink enough to straighten out the panel. Is it in a warm dry area?Greg,
I veneered it about 3 weeks ago; one would think that it would dry by now. It is in a room temp dry area.


I see your problem. Even if you kerf it as Rob suggested, you need a way to hold it flat while you attach the edge molding. You could kerf it and then screw some temporary cauls to the bottom to get it straight, then put your molding on. When you have everything "finished" remove the cauls and screw it to the carcass to hold it in place.

If it was mine and I had more matching veneer, I'd do it over with veneer on the bottom. Mike,
I like your idea... this may be the way to go.

[Mike Henderson]

Greg,
I veneered it about 3 weeks ago; one would think that it would dry by now. It is in a room temp dry area.
Before you do more extreme things, I'd really recommend that you try some heat on it. Moisture can stay in the wood for a long time. Go to one of the Salvation Army type stores and buy an old electric blanket (or borrow one from an understanding friend). Wrap it around the panel and set it on high for 24 hours or more. It may not make fix it but it's worth a try before you start cutting.

Mike

[Steve LaFara]

I assume that you were planning on using screws to atatch the top even though you mention glue???? If you make the screw holes in the top stretcher elongated, you should be able to tighten, shift, tighten again, shift if needed, etc, etc., to get it lined up properly. If the cup is not too bad, the screws should get rid of it. Once it's installed and flat, you can apply the edge banding or solid wood edge. May work, may not. Either way, it won't take much time to find out. Good luck.

Disclaimer...........I would make a new top if you have enough material.:rolleyes:

[Joe Jensen]

It isn't a problem inherent with the veneer on only one side. Really, the problem is adding an extra layer of adhesive to only one side. Nearly all adhesives will change in volume as they cure (generally shrinking rather than expanding)....and hence have a bit of tension in the adhesive once cured. This tension tries to pull into the middle of the panel since the adhesive want s to shrink....use and adhesive that wants to expand and the veneered side will crown rather than cup.

The adhesive causing warp is why plywood has an odd number of layers of wood veneer (veneer core, obviously).....but and EVEN number of layers of adhesive. If the wood was the culprit for causing warp and not the adhesive, you'd balance the layers of wood veneer core and not worry about balancing the layers of adhesive.

WOW Tim, great explanation. Thanks...joe

[Alex Berkovsky]

I assume that you were planning on using screws to atatch the top even though you mention glue???? If you make the screw holes in the top stretcher elongated, you should be able to tighten, shift, tighten again, shift if needed, etc, etc., to get it lined up properly. If the cup is not too bad, the screws should get rid of it.Actually, I was going to glue it; I am thinking that it would be difficult to predrill and run the screws with the little space available to work with.


I appreciate all the advise given. Starting to think of lining up the veneered top on the dresser and glueing it down with cauls and clamps to flatten it. Once glued, I will plane the molding down to final thickness and glue it around the veneered top.