Laminating "Thick" Veneer - Do I Need to Vacuum Bag?

[Marty Tippin]

I'm working on a project where I'm resawing veneers about 12" wide and planing to ~1/8" thick, with the intention of laminating the veneers on both sides of a 1/4 or 3/8" substrate to build up a 1/2 or 5/8" panel.

Not sure whether I can effectively get this done using clamps only, or if I would get better/faster results with a vacuum bagging system. Already have the vacuum pump, so it's not a huge cash outlay to get set up with a bag - but if it's not necessary, I probably won't go to the trouble. I've done a little bit of research regarding the use of vacuum bags but really don't know much about it at this point.

Appreciate any advice that might get me pointed in the right direction!

[Mel Fulks]

I would ( and have ) used Weldwood plastic resin glue. Apply to both surfaces, put 'em together, cover with a plastic bag,cover that with a piece of plywood, put spring clamps around perimeter and a weight it the middle. That glue pulls down as it sets.

[john lawson]

Is a vacuum bag necessary, probably not. Would it help do the job, absolutely!!!

About 10 years ago I built a Demilume table featured in Fine Woodworking. The author used 1/8" mahogony veneer and on a round apron. At the time I was teaching a class for the local Woodworking Guild and our class built 6 of these tables using his plan/article. We used a vacuum bag for the veneer and it worked perfectly. He used clamps. Some friends of mine were taking a stringing class later from this author and questioned him about the veneer method. He admitted to them that he would have used a bag but Fine Woodworking wanted him to use a more traditional method.

If you plan on doing more veneer work or get into bent laminations then I would recommend you treat this as an opportunity to get a vacuum bag. Good luck either way.

[Mike Henderson]

The "safe" approach is to get a bag - they really work well. But if you use lots of clamps, and cauls to pull the center down, it will work. I did it that way before I got a bag.

Mike

[Brian Holcombe]

I did a project with a lot of veneers of this size and larger and about that same thickness. I used a bag but I wouldn't say it can't be done without it (I don't know). I used cold press glue and when that ran out at the last minute I did the last few panels with Titebond III. Both worked fine, the cold press glue a little easier to deal with in the press. Titebond required more time in the press IIRC.

I've used wood weld, or attempted to before, I can never get it right so I just stick with what works for me.

[Larry Edgerton]

I have done it both ways with equal success. I use epoxy usually, but that is just me, I like epoxy. I have made slightly curved steel cauls, wood cauls, and the bag. 373653

For example on this one with 1/8" makore veneer it was too hard to get perfect fits of the wedge shaped pieces using a bag. What I did was apply every other one using a bent steel caul, then did the remaining ones by tapping up into place. There was a center bolt to pull down the cauls in the center.

[Mel Fulks]

With an area that small you could use PVA glue. But the plastic resin is thin and,I think ,less messy.

[Bill Adamsen]

If you already have the pump (as you indicate) vacuum bagging is a no-brainer. It is easy and the results consistent and excellent. If your finished product is flat, you can use a single-sided plastic film on a platen such as plywood or preferably plastic, or more convenient in practice is an appropriately sized bag. If the result needs to be flat you would likely use a platen in the bag. Vacuum significantly slows the cure time on aliphatic glues though I'm not certain why from a chemistry perspective. To my knowledge their strength derives from cross linking as a result of drying (not oxidizing). But my experience from practice is that that bagging slows the cure process.

I have frequently laminated 1/16" and up to 1/8" with no difficulties. Typically I use epoxy which has more predictable cure time in a vacuum environment, and better gapfilling qualities.

Good sources for supplies are Jamestown Distributors (boats) and Fibreglast.

[Mike Ontko]

For an earlier bookcase project (view pics in my album: Bookcase - IKEA Valje copy (http://sawmillcreek.org/album.php?albumid=865) ), I used contact cement and a j-roller to apply a 3/16" thin veneer of CVG Doug Fir to a substrate of 3/4" birch plywood. I decided on contact cement based on a number of posts I'd read on this board and on a couple of other well used woodworking related message boards. In this case the veneer is thick enough that there's no risk of bleed-through, though it's still thin enough that grain movement isn't a significant issue. The reason for the vacuum bag method is to ensure an even distribution of pressure across the entire surface of the lamination. Likewise, you can achieve something close to that even distribution using a cover sheet of some kind (plywood, for example). I'd read that a veneer roller is more effective than a j-roller because it applies the pressure force over a smaller area. That pressure is intended to ensure the veneer and substrate materials are making contact, and to force out any air bubbles that might be trapped between. In my case, I was more concerned about scratching or compressing the relatively soft Doug Fir, so the rubber of the J-roller and it's wider dimension seemed like a better alternative.

[Bill Adamsen]

Larry's point is good ... not everything is a candidate for vacuum bagging. If using a true bag, the "wet" assembly needs to be able to be picked up and installed in the bag while wrapped with breather fabric. When done you will want confidence that nothing has shifted. Typically a one sided film (or mechanical cauls) is easier to apply if there is a fragile glueup.

Mike actually touched on the first thing I thought of ... contact adhesive. It is very fast and if the specifications work, that's a real alternative.

[Marty Tippin]

Thanks for the replies. I believe I'll go ahead and order the few additional bits I need to set up a vacuum bagging system and see how it goes.

I did some more research this morning and, given that I'll be using a thicker veneer (1/8"), it seems there's a good chance that contact cement wouldn't stand up to seasonal movement of the veneer; in fact, joewoodworker.com recommends using a PPR (pre-catalyzed powdered resin) glue for shop-sawn veneers specifically because of it's additional bonding strength. So I'm gonna give that a try as well.

[Kerry Wright]

Marty,
Please let us know how it turns out. I am about to embark on a similar adventure with 1/8" veneer only without the vacuum system.

[Mel Fulks]

Contact cement is made to last about 10 years ,and the reps will tell you that. Yes ,sometimes it can last longer.

[John TenEyck]

You will be happy you got a vacuum bag set up. Flat work, curved work, it can do it all.

I'm glad you saw that comment by Joe W. with regards to PPR glue. I had a very bad experience with his Cold press glue with 1/16" thick shop sawn veneer. Total disaster actually; I'll never use that stuff again on shop sawn veneer.

I like Weldwood Plastic resin glue (PRG) for shop sawn veneer. 1/16" for most interior work, 1/8" for interior door skins, and 3/16" for exterior door skins. If you read the literature for that product you want a lot of pressure to affect a good bond and minimum glue line at the recommended coverage. A few hand clamps around the edges of a large panel won't do it. Cauls might get you there, but the vacuum bag is a far better and easier approach, even though the absolute pressure is less than Weldwood recommends. For hand clamping epoxy is a far better approach because you don't need, nor really want, high pressure. Epoxy works great in the vacuum bag, too, and I would probably use it exclusively if the cost were not high compared to PRG.

One last tip. If you have to make up edge seamed panels of shop sawn veneer, glue the edges before gluing them down to your substrate. That will prevent any unwanted opening of those seams. Learned that one the hard way. TB III works fine for that.

John

[Mel Fulks]

Clamps around the edge won't work without a weight in the middle. The plastic resin glue pulls down as it sets. That was shown to me many years ago. The cautious can add a couple more weights. Bags and pumps will soon be FREE as current owners dispose of them to buy new ones that will serve as clamps for gluing , making all their clothes fit in a pic nic basket, and curing "dysfunction". But not all at one time.

[Mike Ontko]

Contact cement is made to last about 10 years ,and the reps will tell you that. Yes ,sometimes it can last longer.

I hadn't thought of that (yeow!). But then, like the IKEA original I patterned my bookcase after, I didn't really expect it to last beyond 10 years ;)

[Mike Henderson]

Contact cement is made to last about 10 years ,and the reps will tell you that. Yes ,sometimes it can last longer.

Amen to that. Do not use contact cement on raw wood veneer. Contact cement is intended for millwork applications. And as Mel said, it often starts to come apart too soon.

Almost any furniture glue can be used with veneer. I've used PVA, epoxy, cold press, and urea formaldehyde. They all work well in the proper setting. Epoxy is good because it doesn't contain water, and water makes veneer expand. When doing a radial match, water based glues can be a real problem.

Mike

[Jim Becker]

I agree that the vacuum system is ultimately the best solution to use for this kind of thing because of its ability to provide even pressure over the entire workpiece. For flat pieces, using platens to surround the workpiece essentially creates a "clamp" over the whole thing. I use MDF for that.

[Robert Cherry]

Vacuum bagging is a no-brainer, If you have a vacuum pump you already have the most expensive part. I've made bags from heavy plastic drop cloth taped closed with clear packing tape. A bit leaky but worked well. I bought one of Joe Woodworkers vacuum bags for my most recent veneer project and it is a very nice bag, worth the money.

Also be careful how thick you go on the veneer. I've been told by people with much more experience with veneer than me that anything over 1/16" starts to behave more like solid wood than veneer. This is particularly a problem if you are joining multiple pieces of veneer since the joints can open up or the glue line can telegraph proud of the surface as the thicker veneer moves with moisture changes.

I also prefer the urea formaldehyde glues mentioned already. I've used the Weldwood and the Cat-5 with equal success. They are the same product from what I can tell.

Good luck!

[John TenEyck]

You have to be careful using solid cauls over shop sawn veneer, actually any veneer, if it has thickness variations. If the thickness is not dead constant the solid cauls will bridge over the low spots and those low spots will not get pressed and end up poorly or completely unbonded. Breather mesh between the cauls and veneer will prevent this. But at that point you only need a bottom caul with breather mesh on both sides of the veneered substrate and the bag directly on top. That gives you a flat panel with the most uniform pressure possible on every square mm.

John

[andy bessette]

With epoxy glue I simply use weights.

[Mike Henderson]

You have to be careful using solid cauls over shop sawn veneer, actually any veneer, if it has thickness variations. If the thickness is not dead constant the solid cauls will bridge over the low spots and those low spots will not get pressed and end up poorly or completely unbonded. Breather mesh between the cauls and veneer will prevent this. But at that point you only need a bottom caul with breather mesh on both sides of the veneered substrate and the bag directly on top. That gives you a flat panel with the most uniform pressure possible on every square mm.

John

I use carpet padding under a caul - the "rubber" type of carpet padding that looks like it was made from small pieces of different color foam. Of course, I put a layer of plastic under the padding so if any glue comes through, it won't glue the padding to the veneer. I find that gives me good even pressure.

Paul Schurch uses a heavy cloth, like sailcloth, and that works also.

Mike

I never tried it, but I have some fairly thick cork in roll, about 3 feet wide. I could glue that to the underside of a caul and that would probably work, also.

[nate graham]

I'm really surprised no one has brought up Unibond one, we've been using it since its inception, we've had excellent results both with veneering (thick and thin veneers) as well as bent and straight laminations, the unibond has a very hard glueline and is thick enough to prevent bleed through (to a point), with a one hour press time,
We always go for the bag or press, if your only a few parts away from using a pump I would recommend it, big time saver along with solid results.

[John TenEyck]

I took a similar approach, Mike; I used a 1/8" thick closed cell foam silicone mat that has about 25% compression at 10 psi. That worked great, but then I realized that the better approach is to use breather mesh. The reason the breather mesh is superior is because it lets the vacuum come between the caul and veneer so you get absolutely equal pressure on every square mm. Your carpet padding may in fact do the same thing if it's open cell, as would sailcloth. I'm actually using heavy duty plastic window screen material which is really cheap and lasts a very long time. In any case, two cauls is unnecessary. I'm not sure even one caul is needed for flat work if your bench is flat. It does no harm, but I'm not sure it actually does any good.

John

[Mike Henderson]

I took a similar approach, Mike; I used a 1/8" thick closed cell foam silicone mat that has about 25% compression at 10 psi. That worked great, but then I realized that the better approach is to use breather mesh. The reason the breather mesh is superior is because it lets the vacuum come between the caul and veneer so you get absolutely equal pressure on every square mm. Your carpet padding may in fact do the same thing if it's open cell, as would sailcloth. I'm actually using heavy duty plastic window screen material which is really cheap and lasts a very long time. In any case, two cauls is unnecessary. I'm not sure even one caul is needed for flat work if your bench is flat. It does no harm, but I'm not sure it actually does any good.

John

I'm going to look for that heavy duty plastic screen material, John. That sounds like a good idea. Where did you find it?

I've been using screen for breather mesh but the regular screen material. It works as breather mesh but is too thin for anything else.

Mike

[Jim Becker]

I got my mesh from Joe Woodworker

[John TenEyck]

I'm going to look for that heavy duty plastic screen material, John. That sounds like a good idea. Where did you find it?

I've been using screen for breather mesh but the regular screen material. It works as breather mesh but is too thin for anything else.

Mike

I get it at Home Depot, Mike. It's available in several different widths and lengths, too. Look for the stuff labelled Pet Screen. You'll see how much thicker it is.

John

[Mike Henderson]

I got my mesh from Joe Woodworker

I got some from Joe, also. But it's fairly expensive from him. What John is saying is that the heavy duty plastic screen is really inexpensive.

Mike

[Bill Adamsen]

Interesting idea on the screening. Trying to think of a situation where that would be a good solution for my process. Does someone have a diagram?

For me, if doing something flat I use a kerfed platen inside the bag to provide vacuum equalization underneath the object being glued. I suspect that is the function for which you are using the screening? If I add breather fabric between platen and object it serves to absorb glue squeeze out. It doesn't seem like a good practice since it could reduce flatness.

Trying to think of pros and cons of having the equalization inside or outside the platen. Joe Woodworked shows it outside, but I typically put it inside. I guess I worried the bag would close off the kerfs.

If I'm doing a wet layup – bagging on a "skin" of resin impregnated cloth – and want that to conform to the shape without inducing flatness, I would wrap entirely first with the release (peel ply typically) film, then with flexible polyester breather. The release film provides a secondary adhesive surface and minimizes excess resin. That's my standard approach for making say, a foil. I'm pretty liberal with the breather because it is quite inexpensive. Sometimes in a jam I use clothes for breather.

[John TenEyck]

I got my mesh from Joe Woodworker

The problem with his product is it's really coarse and stiff, and if you get a wrinkle in it it's impossible to get rid of. The window screen mesh is much more compliant, available locally, and cheaper.

John

[Jim Morgan]

The problem with his product is it's really coarse and stiff, and if you get a wrinkle in it it's impossible to get rid of. The window screen mesh is much more compliant, available locally, and cheaper.

John

My wife refuses to iron anything, so I commandeered the family iron for my workshop. I use it mostly for hot-melt edging, but set at moderate heat it also serves to smooth wrinkles in breather mesh.

[John TenEyck]

Bill, if you put the mesh outside of the platen it will equalize the pressure on the platen, but do nothing to equalize the pressure on the veneer, glue, substrate interface. If the veneer and substrate are of constant thickness, it's all good. However, the veneer and substrate often are not perfectly flat and, if they aren't, you will have areas that could see low or even no pressure. But if you put the mesh directly outside the veneer every square mm will see the same pressure and the bond will be good as long as the glue was sufficient and well distributed. Yes, if the substrate or veneer has thin spots there will be thin spots after it comes out of the bag. But I'd rather deal with that than areas with poor/no bond.

John

[Bill Adamsen]

But if you put the mesh directly outside the veneer every square mm will see the same pressure and the bond will be good as long as the glue was sufficient and well distributed.

Interesting point. In a nutshell, the substrate on top of the veneer would dilute the pressure of the bagging. Taking that to the extreme .. sometimes (often) I veneer both sides of a substrate (panel) at once. One has the benefit of being just beneath the breather the other is pressed against the platen, which we're saying is "less effective." Presented with that task would you do two glue-ups?

[Brian Holcombe]

You will be happy you got a vacuum bag set up. Flat work, curved work, it can do it all.

I'm glad you saw that comment by Joe W. with regards to PPR glue. I had a very bad experience with his Cold press glue with 1/16" thick shop sawn veneer. Total disaster actually; I'll never use that stuff again on shop sawn veneer.

I like Weldwood Plastic resin glue (PRG) for shop sawn veneer. 1/16" for most interior work, 1/8" for interior door skins, and 3/16" for exterior door skins. If you read the literature for that product you want a lot of pressure to affect a good bond and minimum glue line at the recommended coverage. A few hand clamps around the edges of a large panel won't do it. Cauls might get you there, but the vacuum bag is a far better and easier approach, even though the absolute pressure is less than Weldwood recommends. For hand clamping epoxy is a far better approach because you don't need, nor really want, high pressure. Epoxy works great in the vacuum bag, too, and I would probably use it exclusively if the cost were not high compared to PRG.

One last tip. If you have to make up edge seamed panels of shop sawn veneer, glue the edges before gluing them down to your substrate. That will prevent any unwanted opening of those seams. Learned that one the hard way. TB III works fine for that.

John

Thanks for writing this, though certainly a bit frustrating to read after the fact. That said I have used it on multiple shop sawn veneer projects without issue thus far even with wide flatsawn panels.

I typically glue them thick then plane them thin. Still, I will heed your advice as it is always on point.

[John TenEyck]

Interesting point. In a nutshell, the substrate on top of the veneer would dilute the pressure of the bagging. Taking that to the extreme .. sometimes (often) I veneer both sides of a substrate (panel) at once. One has the benefit of being just beneath the breather the other is pressed against the platen, which we're saying is "less effective." Presented with that task would you do two glue-ups?

Not sure I understand your question. I try to veneer both sides at the same time whenever possible. Sometimes I stack up two or three veneered substrates with mesh in between. And often I use no caul at all. If your bench is flat it isn't needed. Hopefully, some of that is relevant.

John