Vacuum Veneering Techniques #5
Video that accompanies this
article can be found here
Vacuum Veneering a raised
described here is for use with a standard vacuum veneer press.
Typical vacuum bags are made from polyurethane, more industrial grade
material as compared to vinyl. Both materials are available in .020".
We have used the .020" poly vacuum bag because it is the most
supple and flexible of all the options.
There are two
important factors in the success of this process in addition to the
bag. The shape of the panel and the flexibility of the veneer. The
shape should be a gradual curve and not have a right angle turn near
the top of the cut. Most veneers will generally not bend into the
angle and will either snap or just have a gap, thus not a good
The other factor is
that the veneer must be softened so it bends and does not crack when
being vacuum pressed. We used our VKS veneer softener which is diluted with
an equal amount of water. It is sprayed on both sides of the veneer
then placed in the vacuum veneering bag with plain paper on both sides and a caul
on top. When under vacuum, the moisture gets wicked out from under
the caul and will evaporate faster when under vacuum. You should
change the paper several times to speed up the process.
shows spraying the veneer with the veneer softener.
is placing the wet veneer between several sheets of
paper and placing a caul on top and putting the assembly in the vacuum
press. Change the paper for faster drying time.
Check the moisture
content to be sure you are back to the correct moisture level
(moisture content MC). This is an important step and needs to be
addressed with a moisture meter. If the MC is too high when it's
pressed, the veneer can shrink and when it's out of the press and
fully dried can cause crazing/cracking on the surface. Also, be sure
to measure the center as well as the edges when checking the MC
. When in the vacuum press, the edges will dry faster than the
Once you have
shaped your panel and eased the top edge, apply glue to the
substrate. We are using our VAK Bond 2000 veneering glue, a urea glue which is the
type of glue recommended for veneering and laminating.
It should be noted that most of the plywood's, MDF, etc., are made
with urea glue as it has better characteristics than a typical yellow
or white glue. If you are using a birds eye or other veneer with
holes in it, you can minimize the glue push thru by allowing the glue
to set-up for a few minutes. Less moisture will mean less push thru
as it will evaporate and be absorbed into the substrate. How long you
leave it open will depend on; the glue, temperature/humidity of your
shop, how much glue was applied, the veneer, etc., you will need to
test if this is an issue with you.
Also, if your birds
eye is a light color and you are using the VB2000 veneering urea glue, consider
adding a white tint to make it almost white. By controlling the
amount of white tint that is added, you can go from the dark brown to
Pressing a single
sheet of veneer verses a spliced sheet made of two or more pieces, is
slightly different. For the single sheet, lay the veneer on the panel
and smooth over the top surface to remove any bubbles or wrinkles.
Slide the assembly into the bag and pull vacuum. Make sure the bag
does not have any wrinkles over the veneer. We are doing it without
the usual caul because it's difficult to make a caul to totally fit
the panel. We can easily smooth out any wrinkles in the bag before it
is fully evacuated. When the bag is pumped down, you will see slight
wrinkles in the veneer in the four corners. Because the veneer has
been softened, it is pliable and these wrinkles can be pushed out with
your thumb. Just work each corner until the veneer is down on the
substrate, it only takes two or three rubbings to get it flat.
If you are vacuum pressing
a book matched veneer or sheet that has been taped together (use
veneer tape only), then you need to include another step. Once you
put it in the vacuum bag, as vacuum is being applied smooth over the
bag on the top of the panel. Then take and push the bag up around the
sides so as to raise the bag like it has a bubble all around the edge
of the panel. The reason for doing this is that we have seen some
pulling apart at the seam if the outer edge gets pressed at the same
time as the top. It doesn't always happen. However, it's worth the
extra step to have the bag press on the top surface first and thus
hold it in place before the edges start getting pressure. Then rub
out the wrinkles in the corner.
Allow the glue to
dry according to the manufacturers instructions. Remember, you can
speed the cure time of any glue by applying heat. We have used an
electric blanket on top of the bag with another cover blanket covering
it and have reached 100 degrees F with this method.
is the finished piece.