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Breather mesh is an extruded plastic fabric that is used in a vacuum bag to allow air to flow away from the project being pressed and towards the vacuum port (valve stem). It is used in place of a top platen/caul. Without it, the vacuum bag material can seal itself against the veneer causing pockets of air. These pockets have little or no pressure inside and therefore do not provide enough clamping strength for veneer work. By using breather mesh, you allow the vacuum pressure to evenly distribute throughout the bag. This is the key to successful vacuum pressing.
Breather Mesh Advantages
- Light weight
- Inexpensive
- Re-usable
- Allows you to see the veneer as it is being pressed
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- Does not fatigue the bag material
- Reduces bleed-through artifacts
- Easy to use, cut, and store
- Will not stick to most veneer adhesives
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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.
Small Project with a Large Platen
If you have a small project to veneer, you may not be using the full capacity of a vacuum bag. In this case, insert a platen and place your veneer on top. Then place the breather mesh over the entire veneer surface a few inches to overhang at the edge closest to the bag opening. Position the entire assembly so that the valve stem on the bag is above the overhanging breather mesh. This will allow you to evenly distribute vacuum pressure over the veneered panel. See the picture below.
Keep in mind that you can (and should) veneer the back side of the substrate at the same time as the face veneer. You do not need breather mesh on the back side of the panel. The platen itself will prevent any air pockets from forming.
Figure 1 : Pressing cherry veneer to 1/4" plywood.
Note that the bottom platen is larger than the project panel.
Large Project with a Large Platen
When a large project is being pressed in a vacuum bag, you may not have room in the bag to allow the breather mesh to overhang. In this case, place the breather mesh over the entire veneer surface. The valve stem will have to sit over the veneer and may leave a mark on the veneer when pressure is applied. Remedy this by placing a 4" x 4" piece of ¼" plywood on top of the veneer and then adding a 5" x 5" square of additional breather mesh over the ¼" plywood as shown below.
Figure 2: Pressing maple burl veneer to 1/4" plywood.
Veneer Positioning With Breather Mesh
Burl Veneers
Flat or Contoured Panels |
Non-Burl Veneers
Flat Panels |
Non-Burl Veneers
Contoured Panels |
Face veneer up
(against the breather mesh) |
Face veneer up
(against the breather mesh) |
Backer veneer down
(against the platen) |
Backer veneer down
(against the platen) |
Backer veneer down
(against the platen) |
Face veneer up
(against the breather mesh) |
This position minimizes
bleed-through issues as
noted below. |
The platen side provides
the smoothest surface and most
even pressure distribution. |
This is the only way to veneer
a contoured panel with
breather mesh. |
Additional Information
When pressure is applied to the veneer, burl veneers will sometimes allow small amounts of glue to pull through the veneer face. This is often referred to as "bleed-through". One of the great aspects of breather mesh is that it reduces any adhesive bleed-through artifacts. With a standard platen or caul setup, the glue that bleeds through is forced back down into the veneer face creating a splotching effect which can be very difficult to remove. 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 "painted" with the veneer adhesive. When applied correctly, you should be able to see a small amount of the substrate through the wet glue layer. I prefer to draw a few lines on the substrate before applying the glue. Then I use a roller to spread to glue until I see the pencil lines.
Even with the correct amount of adhesive, some bleed-through is possible. However, with the use of breather mesh, the glue is not pushed back into the veneer face. Instead, it stays in a tight micro-bead on the surface of the veneer which is easily sanded or scraped off with a minimal amount of effort. After the excess glue 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.
Bleed-through with a platen or caul |
Bleed-through with breather mesh |
One Thing to Note
Breather mesh may leave small impressions in softer woods such as walnut and pine which can be sanded off easily. If this is a major concern, reduce the maximum pressure from your vacuum press system to 18" of Hg. To get rid of the impressions, you can steam them out with a clothes iron on the medium heat setting. Spritz the veneer face of the panel with water (after the glue is fully cured) then iron lightly.
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