Cast off the damps and cauls. The power of atmospheric pressure puts damping success in the bag.
Veneer provides the perfect way to add exotic species and special grain to projects.
Gluing veneer to large panels requires the application of clamping pressure evenly over broad areas to ensure a good bond with the substrate. Woodworkers usually rely on platens, clamps, cauls, and a hectic scramble to get everything clamped up before the glue starts to set.
PERFORMANCE UNDER PRESSURE
Vacuum-bag clamping simplifies veneering large panels by using the power of atmospheric pressure to provide clamping force. Atmospheric pressure is always pushing on everything on Earth at 14.7 pounds per square inch (psi) at sea level (and slightly less at higher elevations). That pressure doesn’t crush objects on Earth because air inside the objects pushes back to equalize the force-unless you remove that air, a process called creating a vacuum.
A vacuum-bag clamping system does exactly that. By placing your panel glue-up in a sealed bag and connecting a vacuum pump to remove the air, you can put that 14.7 psi to work for you. Best of all, vacuum clamping applies that pressure consistently inside the bag.
That means you get a flat panel with no bubbles, compressed spots, or glue-starved areas.
Bag-and-pump systems exist to suit many needs and budgets. Learn more about them in Selecting a System. In addition to the pump and bag, you only need a few other items. See In the Bag-and Beyond.
BAG IT UP TO GLUE IT DOWN
Before you spread glue on your substrate, make sure your veneer is flat. Burls and crotch veneers commonly have ripples or puckered areas. Eliminate them by spraying the veneer with softener [Sources]. Sandwich the veneer between paper towels or kraft paper, and then clamp it between a pair of plywood or MDF platens overnight or until dry.
After flattening, apply blue painter’s tape to the outside face of the veneer to hold any cracks or tears together during clamping.
Get your vacuum-clamping system and supplies ready to go before you spread any glue. You won’t have a lot of time to get everything into the bag before the glue starts to set.
1. Place your panel substrate on one platen, and then use a roller to spread glue over the surface (Photo A). We like to wrap the platens in wax paper to prevent glue from sticking them to the veneer and substrate. Also round over the outside edges of the platens. This helps the vacuum bag wrap tightly around the platens and eliminates sharp comers that could damage the bag.
2. Lay your veneer on the substrate and press it lightly into place, making sure to position it w’here you want it (Photo B).
3. If you’re veneering both faces, flip the substrate over on the platen, spread glue, and apply the veneer as you did on the first face (Photo C).
4. Position the second platen to sandwich your veneered panel, and then slip the sandwich into the vacuum bag (Photo D), You need to create your sandwich and get it into the bag before the glue begins to set, so work quickly but carefully.
5. Seal the open end of the vacuum bag using the closure. This bag uses a PVC tube the bag rolls over, plus a C-channel that clips over the top (Photo E).
6. Connect the pump to the bag fitting and turn the pump on. It pulls the air out and maintains vacuum pressure while the glue dries (Photo F). Glue drying time remains the same inside the bag. So, you can remove your panel from the bag in 45 to 60 minutes.
7. Shut off the pump, open the bag, and remove your panel. Use caution when peeling off any painter’s tape, because it may have become stuck to the glue.
Now you can cut your perfectly veneered panel to size to add pop to your project. And you’ll know that the veneer is well adhered, so you don’t have to worry about loose edges or bubbled areas in the future.
With a vacuum-bag system, you’ll also have newfound clamping abilities that allow you to do much more than create flat panels. You can veneer curved surfaces, create bent laminations, and even use the pump to add vacuum-activated holding capabilities to benches and shop fixtures.