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Necessary to veneer both sides of a 1-1/2” thick laminated plywood substrate?

by IsaacJames
posted 10-12-2018 03:15 PM


28 replies so far

View TDHofstetter's profile

TDHofstetter

4 posts in 226 days


#1 posted 10-12-2018 03:32 PM

If you don’t add some sort of veneer to the underside, then the plies won’t be balanced and any humidity shift may encourage some warping. Even if you need to buy some nasty junk veneer for the underside, veneer it. The surface plies should always be the same thickness and in “grain agreement”.

-- -- Tim --

View DS's profile

DS

3145 posts in 2784 days


#2 posted 10-12-2018 04:14 PM

When laminating you should ALWAYS make balanced panels.
It is important to have the same treatment on the front face as the back face.

No matter how strong you think your substrate is, an unbalanced panel is doomed to failure.

There are plenty of acceptable backer sheets that can be used instead of expensive veneers in order to balance your panel.
Polybak sheets are super stable and relatively cheap. (About $9 per 4×8 sheet in my area)

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View Andybb's profile

Andybb

1900 posts in 967 days


#3 posted 10-12-2018 04:56 PM

As you said, you are a pro and I am definitely not but …. 1 1/2” seems pretty darn thick to worry about veneering the underside. Especially since the underside is a completely different sheet of ply from the top side. Almost as if the plywood is 3/4” veneer. Good chance that I am wrong but I would think that veneer attached to a seperate sheet of plywood would have very little connection to the veneer on the top.

Interested to hear responses.

-- Andy - Seattle USA

View oldnovice's profile

oldnovice

7475 posts in 3732 days


#4 posted 10-12-2018 06:10 PM

I was taught and always followed “balance” whether veneer, finish, or paint.
Hasn’t let me down so far!
But that was 60+ years ago …. maybe things have changed?

-- "I never met a board I didn't like!"

View Aj2's profile

Aj2

2211 posts in 2162 days


#5 posted 10-12-2018 06:30 PM

Of course you should treat both sides equally.What could be the downside the cost of a cheap veneer and the time it takes. Hardly worth the risk of a cupped panel.
I’m sure there’s ways around using ridged glues but then there a whole new set of issues that come up.

-- Aj

View DS's profile

DS

3145 posts in 2784 days


#6 posted 10-12-2018 06:36 PM

It is a known fact that wood is a natural material that moves and breaths with changes in temperature and humidity.

It wouldn’t matter if your substrate is 12” thick, if there are uneven stresses in the panel, it will move accordingly over time.

I am not saying it wouldn’t take a bit longer, but it WILL move – 100% guaranteed.
Will it stay straight and flat as it moves? That depends if it is balanced or not.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View gwilki's profile

gwilki

293 posts in 1838 days


#7 posted 10-12-2018 07:10 PM

I don’t have an answer, but I hope you don’t mind a question for all of those who say that you need to veneer the bottom.

Since the top is made up of two sheets of plywood, what is the difference between a piece of veneer that the OP would add and the outer “veneer” or ply on the sheet of plywood in terms of how moisture will affect the piece?

I’m not arguing one way or another, and I am not a professional by any stretch of the imagination, but I really would like to understand this. The outer ply on the plywood is really just a sheet of veneer, is it not? It may be a bit thicker than some veneer, but other than that, it’s just a thin layer of wood, just as veneer is. So, why would adding another piece of veneer to the plywood substantially change the way it is affected by humidity?

-- Grant Wilkinson, Ottawa ON

View MrRon's profile

MrRon

5440 posts in 3607 days


#8 posted 10-12-2018 07:33 PM

Kitchen countertops have a laminate on one side only, yet they don’t warp.

View Aj2's profile

Aj2

2211 posts in 2162 days


#9 posted 10-12-2018 07:37 PM

When the plywood was made they veneered both sides correct.? The smart guys know without doing this the panel would warp straight out of the press.
Now the op wants to upset this balance so it needs to be equally treated on both sides.

I will now attempt a scientific guess to what happens when we add water based glue to One face of a sheet of plywood

Glue is absorbed into sheet, the cells puff up into their natural shape everything is happy. Panel is removed from clamps air is now in contact with surface. And panel starts shrinking as water starts leaving unhappy cells. A bazillion cells all shrinking a tiny bit adds up and pulls the whole substrate into a unknown shape that’s not anywhere near flat.
I rest my case :))

-- Aj

View Fred Hargis's profile

Fred Hargis

5507 posts in 2857 days


#10 posted 10-12-2018 08:38 PM

I suggest you veneer the bottom, but nothing says it has to be walnut. After all, if you didn’t veneer it , wouldn’t it be what ever the plywood veneer is? There are “backer” veneers made just for this, get some of that and use it.

-- Our village hasn't lost it's idiot, he was elected to congress.

View MrRon's profile

MrRon

5440 posts in 3607 days


#11 posted 10-12-2018 09:26 PM



Kitchen countertops have a laminate on one side only, yet they don t warp.

- MrRon


On second thought, counter tops are not plywood, but MDF or particle board.

View clin's profile

clin

1027 posts in 1360 days


#12 posted 10-12-2018 09:53 PM

I agree with adding a similar veneer to the bottom. Though I don’t think it needs to be expensive wood or even walnut. Though I would use a wood with similar expansion characteristics to walnut and the same thickness as the top. And of course this would need to be cut similar to the top veneer.

Also, when I think veneer, I think of something thinner than 3/32”. I think 3/32” is thick enough to matter.

Concerning the two layers of plywood, run their outer grain the same direction. I think some might think that you should alternate them, just as the inner layers are, but it won’t be balanced that way. Running them the same just means the inner layer will be that much thicker and effectively have the desired odd number of plies.

I also can see where this might be a belt and suspenders type thing. But you are not manufacturing a thousand of them, you are making one. And you have to get it right the first time. So best to err on overdoing it.

-- Clin

View IsaacJames's profile

IsaacJames

6 posts in 226 days


#13 posted 10-12-2018 11:07 PM

Thank you all so much for your responses, I really appreciate it.
I agree with everything you all said. I completely understand wood movement in reference to veneer and plywood. I agree that veneer should indeed be applied to all sides. That being said, I also see how the second sheet of 3/4 ply could indeed act as a veneer itself considering it would be glued the same way as the top layer of walnut veneer.
However….begrudgingly I have decided to add a layer of cheap veneer to the underside of the bottom piece of substrate as an insurance policy.
Now, let me ask you all another question:
My client would prefer to have to table slightly distresssed looking. She doesn’t want it to look like a brand new piece bought from a factory showroom.
So, instead of applying the 7-1/4” wide X 32” long strips of Walnut veneer to a sold sheet of plywood, what about ripping the top layer of plywood into matching 7-1/4” X 32” pieces, glueing the veneer to them (top & bottom) and either glueing or cabinet screwing those individual veneered strips of plywood to the bottom piece of solid 3/4 ply? My thought in doing this is to create a “pieced together” effect to the tabletop as if it were built out of individual boards vs. glueing all of the veneer pieces to a single large piece of plywood giving it that typical smooth veneered look.
Do you think this would give me the effect I’m looking for or do you think this would just create a cluster of other problems?
Aaaaannd….......GO!!

-- | Measure Once, Cut Twi |

View IsaacJames's profile

IsaacJames

6 posts in 226 days


#14 posted 10-12-2018 11:48 PM

@ DS:
I really like your quote!

-- | Measure Once, Cut Twi |

View shipwright's profile

shipwright

8293 posts in 3162 days


#15 posted 10-13-2018 02:30 AM

First: I would, to be safe, put some kind of veneer on the back.
However, if it were me, I’d be doing a sample to keep around the shop with veneer only on one side.
I’ve done a lot of veneering and I don’t think this will warp. You have at least 14 glue lines. The more layers in a lamination, the more stable it is.
Gut feeling, I don’t think it moves at all.

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese! http://thecanadianschooloffrenchmarquetry.com/

View JAAune's profile

JAAune

1864 posts in 2681 days


#16 posted 10-13-2018 04:42 AM


Kitchen countertops have a laminate on one side only, yet they don t warp.

- MrRon

On second thought, counter tops are not plywood, but MDF or particle board.

- MrRon

Laminate counter can warp if it’s not fastened to something rigid like a cabinet box. I’ve always used laminate backer to avoid the issue. It’s the same phenolic material used for laminate but without the decorative plastic coating.

Phenolic CNC tables are prone to warping too which is why aluminum tables are preferable.

-- See my work at http://remmertstudios.com and http://altaredesign.com

View Richard's profile

Richard

11274 posts in 3397 days


#17 posted 10-15-2018 01:41 AM


Kitchen countertops have a laminate on one side only, yet they don t warp.

- MrRon

This is TRUE!! I also don’t think Yours is going to move.

-- Richard (Ontario, CANADA)

View Richard's profile

Richard

11274 posts in 3397 days


#18 posted 10-15-2018 01:45 AM


I was taught and always followed “balance” whether veneer, finish, or paint.
Hasn t let me down so far!
But that was 60+ years ago …. maybe things have changed?

- oldnovice

“But that was 60+ years ago …. maybe things have changed? YES! They certainly have! :-}

-- Richard (Ontario, CANADA)

View Lazyman's profile

Lazyman

3339 posts in 1751 days


#19 posted 10-15-2018 01:49 PM

+1 one on adding some veneer to the bottom but how are you going to glue up the panel in the first place? I am actually more concerned with how you are planning to glue 2 large 3/4” sheets of plywood together than with the veneer causing the warpage. I’ve seen more reports of warping problems caused by improperly gluing and clamping sheets of plywood than with imbalanced veneer. Any reason you can’t leave the panel a single thickness of plywood?

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View IsaacJames's profile

IsaacJames

6 posts in 226 days


#20 posted 10-15-2018 05:09 PM

Hey Nathan, As I stated in my second question on this thread, I’m considering ripping the top sheet of 3/4” plywood into strips that match the veneer I’m applying to them. This would prevent having to glue two full sheets of plywood together and creating the issue that you’re concerned about.
Here is a screenshot of my SketchUp drawing to help visualize what it is I’m building if you all think that’ll help. The veneered pieces are the 10 interior boards and center cross piece. The 2 outside edges and the breadboards will be solid wood.

Thoughts?

-- | Measure Once, Cut Twi |

View Aj2's profile

Aj2

2211 posts in 2162 days


#21 posted 10-15-2018 06:09 PM

It think that will work just fine. So long as the solid wood is on the outside perimeter.
And if you have the skills to make all the square cuts. :)

-- Aj

View IsaacJames's profile

IsaacJames

6 posts in 226 days


#22 posted 10-16-2018 12:26 AM

Thanks Aj,
I appreciate your input. Looks like everyone else has lost interest :D
I think I’ll move forward with my idea; seems like it gives me the best of all worlds. I’ll let this thread know how it pans out.
Thanks everyone!

-- | Measure Once, Cut Twi |

View Lazyman's profile

Lazyman

3339 posts in 1751 days


#23 posted 10-16-2018 04:14 AM

Isaac, it just seems to me that you may be making it more complicated than it needs to be. As long as your trestle has good support underneath, 3/4” should be thick enough. If you can cut the veneer so that it has straight and parallel sides, I think it will be easier to attach the veneer directly to a single 3/4” .sheet. I am not sure how difficult it is going to be to attach the veneered plywood strips to the full sheet without creating gaps, which could look bad. Any gaps you get are going to allow spills to seep into them and cause other problems. I just don’t think that is a good idea.

BTW, I highly recommend you look into hammer veneering using hot hide glue. It will be the most forgiving method for applying the strips of veneer. As long as your veneer has square and parallel sides, you can easily get perfect joints with this method. It is also reversible which may be important if you have a limited amount of veneer to use. Checkout shipwright’s blogs for more information.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View shipwright's profile

shipwright

8293 posts in 3162 days


#24 posted 10-16-2018 04:52 AM

I think this is the blog Nathan is referring to. It is part of a series on animal protein glues but this segment is about hammer veneering.
There is a learning curve, but it really isn’t that hard to learn.

http://lumberjocks.com/shipwright/blog/36014

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese! http://thecanadianschooloffrenchmarquetry.com/

View EarlS's profile

EarlS

2732 posts in 2712 days


#25 posted 10-16-2018 11:32 AM

Since no one seems to have given an opinion on distressing I’ll throw my 2 cents in. Distressing wood makes it look like it’s been around a while and seen some wear and tear. Generally, that means some dings and dents, maybe a scratch here or there. In other words, let it get banged up somewhat during the build and don’t put quite as much effort into eliminating every nick or scratch. If you are rounding over edges, hit them with a ROS a little heavier here and there to provide a worn, but not abused piece.

Can you do any distressing on the edges of the interior pieces or would that make gaps that would look sloppy rather than distressed? If not, I’d stick to careful surface distressing so it doesn’t go through the veneer. Drop a few nails on it, maybe a nut or two.

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

View Robert's profile

Robert

3374 posts in 1845 days


#26 posted 10-16-2018 02:57 PM

I agree with shipwright I seriously doubt it will warp you’re essentially creating a 1 1/2” thick lam beam.

I would, however rip one sheet in 1/2 and orient the second layer perpendicular to the first.

Have you considered using MDF?

-- Everything is a prototype thats why its one of a kind!!

View 000's profile

000

2859 posts in 1263 days


#27 posted 10-16-2018 03:21 PM

deleted

View IsaacJames's profile

IsaacJames

6 posts in 226 days


#28 posted 10-17-2018 05:48 PM

Hey everyone, thank you for your continuing responses. I appreciate all of your info. I agree that one sheet of 3/4 plywood would be strong enough for this application. However, my client requested that the substrate be 1-1/2” thick. It’s just what she wants so I’m rolling with it. I like the idea of altering directions of the two sheets; it seems like an easy insurance policy to keep it all flat and happy.
I will also look into hammering the veneer. Sounds like a great way to do it. Thanks again guys for all of your input. I will keep you all in the loop and include pictures as I go along just for the hell of it.
Have a good one!

-- | Measure Once, Cut Twi |

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