Vacuum bagging marquetry veneers using epoxy, and dealing with bleed through

[vincent wawrzynski]

Hello All,

I am an experienced composite laminator trying my hand with veneers, specifically burl veneers. My usual first removable layer on top of the composite is peel ply. When the extra epoxy is drawn into the vacuum bag it saturates the peel ply but the tight weave makes tearing it off a simple albeit forceful event. Wetted out fiber always stays together even though the tearing action is strong. I am concerned that I might just be pulling off bits and pieces of the veneer with the peel ply.

Should I be concerned, are there better practices for the first layer on top of the veneer inside the vacuum bag?


Thanks
Vince

[Kevin Jenness]

I'm not familiar with peelply, but a caul that sticks to the veneer seems like a bad idea. I typically use lightly waxed 1/4" or 3/8"melamine coated particleboard on flat work. For curved layups I will use waxed bending ply or plastic laminate.

Normally one tries to prevent bleedthrough of adhesive through wood veneer. That is just about impossible with epoxy under sliced veneer and doubly so with burl. If you want to use epoxy you may as well seal the entire surface with epoxy and sand that back before finishing. That is laborious but it does fill the grain and any voids. Otherwise you may want to try plastic resin glue and experiment with the spread to avoid bleedthrough.

If you are new to wood veneering I recommend Scott Grove's Advanced Veneering for a thorough introduction to the basics plus some innovative seaming techniques for burl work.

[johnny means]

What is the purpose of the peel ply when using veneer?

[John TenEyck]

In a vacuum bag I never use a top caul, curved or flat. I put a piece of plastic over the veneer, then a piece of plastic window screen, then into the bag. I only use shop sawn veneer so I can't vouch if the same procedure works with commercial veneer but I don't see why not.

John

[Kevin Jenness]

There are several reasons why I use cauls over veneer on the top side of a panel, especially with thin sliced veneer. I also use a caul under the veneer and over a grooved base platen, but that is typically the full press size.

One reason is to protect the bag from sharp corners- I round over the edges and corners of the cauls. If I am veneering one face at a time (infrequent) I may just pad the panel corners rather than cut a caul.

Another is to protect the edges of the top veneer from breaking over the panel edge. I usually cut the caul and the veneer about 1/4" larger than the panel to account for any slippage in the press, and the stiffness of the caul protects the veneer overhang.

The major reason is to ensure a flat result. Shopsawn veneer has enough inherent stiffness that it doesn't necessarily need a platen, but sliced veneer at >020-.025" has little rigidity. A platen ensures that any ripples in the glue spread are flattened out as are any waves in the veneer. Veneer can and sometimes must be flattened but it is laborious , and unless pressing is likely to damage a given veneer I will avoid the flattening process. Figured woods and especially burls sometimes have some unevenness that would not be pressed flat without a caul.

Using cauls does take time and material and they aren't always necessary. It's routine for me. I know some people use breather mesh directly on veneer but that seems to me to run the risk of imprinting the mesh texture. Likewise, a solid platen avoids the potential for wrinkles in a plastic sheet directly on veneer, especially in a bag press where the layup is slid in and the layers are harder to control. Again, that would have less effect on a 3/32" sawn veneer than on thinner stuff. They keep slicing the baloney thinner and the flatter the layup coming out of the press, the less sanding is required.

That's my reasoning- I'm open to change, but I've been getting consistent results using platens.

[Mel Fulks]

Most of my veneer work has just been putting patches on old veneered furniture, but I have used platens . I do wonder why the old
veneer hammer method is never mentioned. Much cheaper than using modern presses .

[Walter Plummer]

It is not applicable to veneer lamination. How are you planning to finish your project? Unless you are going to use epoxy as the finish on the project I think any bleed thru will be an issue. I have done some composite work so I am familiar with the materials. Evan if you flooded the surface with epoxy the peelply I have used leaves a textured surface that would need to be sanded and buffed. Also vacuum for veneer is only about 20 Hg. not absolute like infusion. Good luck.

[vincent wawrzynski]

It is not applicable to veneer lamination. How are you planning to finish your project? Unless you are going to use epoxy as the finish on the project I think any bleed thru will be an issue. I have done some composite work so I am familiar with the materials. Evan if you flooded the surface with epoxy the peelply I have used leaves a textured surface that would need to be sanded and buffed. Also vacuum for veneer is only about 20 Hg. not absolute like infusion. Good luck.

The veneer top surface once proof sanded will get saturated with epoxy then a transparent glass weave with epoxy and topcoated with a UV stable Poly. Overkill in most cases but this is decorative seating in a boat that will see foot traffic and the elements.

[vincent wawrzynski]

What is the purpose of the peel ply when using veneer?

First attempt with veneer for me so I can't say there is a good purpose for the peel ply. Its general purpose is to skip a step in post layup finishing. The peel ply will wick a layer of resin above the composite and then pass any surplus resin into the breather material. This gives a uniform resin layer on top of the fiber that often times needs no further sanding. If you use the peel ply right you can simply tear it off and apply your next coating immediately. The peel ply weave is tight enough that while it technically is bonded, the bond points are so tiny compared to the weave that it tears completely free. I noticed another post by someone who is sealing with epoxy alone and wanted to know how to get epoxy to lay flat. Peel ply is the answer to that even if no other fibers or layers are being used. Instead of (epoxy-cure-sand-epoxy-cure-sand-epoxy-cure-sand...next finish) you may achieve (epoxy-cure-next finish)

[John TenEyck]

Kevin, if you use breather mesh (I use heavy duty plastic window screen) you don't need a grooved bottom plate. A flat piece of Melamine is all that's needed. Put the screen under it if you prefer. If you want to use a top caul then just put another piece of window screen over that. Make sure the window screening, both top and bottom, go to the vacuum port so the air can escape. No grooved bottom plate = one less thing to contend with.

I make the veneer the same size or a little smaller than my substrate. I tape it on in a few spots to keep it from moving. It doesn't move. The window screen hanging over the corners of the substrate is enough to protect the bag from the sharp corners; I've never put a hole through the bag from a corner. With the veneer not hanging over the edges there's no need for a top caul, although I understand your motivation to use one with thin, commercial veneer for the reasons you mentioned. I pretty much exclusively use 1/16 to 1/8" shop sawn veneer these days, even 1/32" or less if I have to match an old piece for repair. I've never had a problem with the window screen or a wrinkled piece of plastic imprinting into the veneer. Shop sawn veneer is just so much nicer and easier to work with. Wrinkling, bleed thru, check marks, etc. are never an issue.

John

[Kevin Jenness]

Kevin, if you use breather mesh (I use heavy duty plastic window screen) you don't need a grooved bottom plate. A flat piece of Melamine is all that's needed. Put the screen under it if you prefer. If you want to use a top caul then just put another piece of window screen over that. Make sure the window screening, both top and bottom, go to the vacuum port so the air can escape. No grooved bottom plate = one less thing to contend with.

I make the veneer the same size or a little smaller than my substrate. I tape it on in a few spots to keep it from moving. It doesn't move. The window screen hanging over the corners of the substrate is enough to protect the bag from the sharp corners; I've never put a hole through the bag from a corner. With the veneer not hanging over the edges there's no need for a top caul, although I understand your motivation to use one with thin, commercial veneer for the reasons you mentioned. I pretty much exclusively use 1/16 to 1/8" shop sawn veneer these days, even 1/32" or less if I have to match an old piece for repair. I've never had a problem with the window screen or a wrinkled piece of plastic imprinting into the veneer. Shop sawn veneer is just so much nicer and easier to work with. Wrinkling, bleed thru, check marks, etc. are never an issue.

John

Many ways to skin the cat. I started out with this method following Darryl Keil's lead and have stuck with it. I'm sure yours works equally well.

One reason I use a grooved platen currently has to do with the homemade frame press I use. The aluminum extrusions in the Vacupress frames are quite rigid and the pleats in their membrane pretty much eliminate any lateral pull under vacuum, but my flat silicone membrane tends to bend the long sides into the center. My platen is a close fit inside the frame and prevents the frame distorting. The platen is in two pieces, thus easy to move and is stored in my plywood rack next to the frame.

I worked for a long time with a bag and still have one for curved work, but for flat or slightly curved work the frame press is far easier to load and unload.

I don't know that I have ever holed a bag with an unprotected corner, but it definitely leaves persistent marks and potential weak spots. The plastic sheeting and screen that you use certainly soften the corners.

I have used breather mesh and plastic film and find I prefer a rigid sheet for a caull as it is easier to keep in place and flat, especially maneuvering everything inside a bag. I too prefer shop sawn veneer as a rule but there are many species and cuts available as sliced veneer that would be difficult to impossible to source in sufficient dimensions of solid wood.

[Kevin Jenness]

The veneer top surface once proof sanded will get saturated with epoxy then a transparent glass weave with epoxy and topcoated with a UV stable Poly. Overkill in most cases but this is decorative seating in a boat that will see foot traffic and the elements.

That is a different breed of cat. I suspect you might get more insight from boatbuilders than from most of the woodworkers here. Are there alternative formulations of peelply that release more easily? Is the additional thickness of epoxy deposited under the peelply necessary given the fact that you will be adding another layer of glass and epoxy?