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Thse pockets of insufficient vacuum inside the bag, greatly reduce the clamping strength needed to press the veneer down onto the substrate. By using breather mesh, you allow the vacuum to evenly distribute throughout the bag and this is the key to successful vacuum pressing. A bottom platen board (typically 3/4" melamine) is still required when breather mesh is used, but with this method there is no need to cut grooves in it or to apply the border strip as mentioned on the platens page of this site. To be very clear about this, only a single 3/4" melamine board without grooves is needed if you are using breather mesh. The platen board should be at least as large as you project panel but it can be larger. Some users prefer to have one platen board this is sized to fit their bag and they use that same set up for all projects large and small. The life of the vacuum bag and the mesh can be significantly increased by easing all of the platen board edges using a 3/8" or 1/2" radius round-over router bit. For flat veneer panels, the bottom platen is only used to provide a reference surface which keeps the veneer panel flat while the veneer adhesive is setting up. For flat and curved projects, the mesh acts as a flexible top platen that comforms to the shape of the project. Some users set their vacuum bag and platen board over a pair of saw horses. This can be problematic since the platen board can bend under its own weight. It is better to place the vacuum bag and platen on a flat work bench surface instead. You may be wondering if you can use window screen material as breather mesh. The answer is both yes and no. Window screen material can create a pathway for the flow of vacuum. Several users have sent messages saying they had no issues other than a moderate increase in the amount of time it took to draw full vacuum in the bag. It is important to know that a veneer that is not completely flat is not likely to flatten under window screen material; you can get lumps in the finished panel. The other issue is that any adhesive that bleeds through the veneer will smear back onto the surface of the panel. The breather mesh offered at VeneerSupplies.com has a much wider and open weave than screen material so glue that comes through the veneer beads up and can be easily scraped off. I've also found that breather mesh is much easier to slide into the vacuum bag than screen material. Breather Mesh Advantages
It was once thought that breather mesh was only suitable for curved projects in which a standard caul would not be usable. However, you’ll find this material excellent for use with flat panel veneering as well. Here are some tips for using breather mesh on your next vacuum press project. Breather mesh is typically cut to fit the size of the vacuum bag if most of the user's projects will be flat panels. Curved projects often require a piece of mesh cut to match the panel size. 
The Ideal Set-Up for Most Flat Panels If you have a small project to veneer, you may not be using the full width or length of the vacuum bag. In this case, insert a platen and place your veneer and glued-up substrate on top. Then place the breather mesh over the entire veneer surface leaving a few inches of over-hang at the edge closest to the bag stem. Position the entire assembly so that the bag stem on the bag is above the overhanging breather mesh. This will allow you to evenly distribute vacuum over the veneered panel.
Optional Vacuum Mesh Bridging But keep in mind that the vacuum bags offered at VeneerSupplies.com have a flush-mount stem. In other words, the bottom of the stem does not protrude into the bag. This means you can put the bag stem right on top of the mesh and directly over the veneer. That's why this section is titled "optional".
Veneer Positioning With Breather Mesh
Additional Information The first key to preventing bleed-through is to use the right amount of adhesive with a dedicated veneer glue roller. The surface should be evenly and lightly coated with the veneer adhesive. When applied correctly, you should be able to see the substrate through the wet glue layer. To make this as easy as possible, I draw a few pencil lines on the substrate before applying the glue. Then I use the roller to spread to glue out so I can see the pencil lines through the glue layer. At that point, I know I've used the right amount of glue. Even with the correct amount of adhesive, some bleed-through is possible. This is especially true with burl veneers. However with breather mesh, the glue stays in a tight bead on the surface of the veneer which is easily sanded or scraped off with a minimal amount of effort. After the excess adhesive is removed, the only glue on the face will be that which has filled any voids in the veneer. This is a great advantage and will give you a smoother finished panel.
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Breather mesh
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