I made some rather thick veneer (3/32 to 1/8 thick) and wanted to try
out the iron-on method of coating the base and veneer pieces with PVA,
letting the coats dry then ironing them on. It took quite a bit of
time and heat (cotton setting and about 20 seconds in one place).
The pieces ironed on just fine, but the seam between each piece formed
a gap. I tried to just hold one piece against the other, use a clamp
to hold one piece against the other, veneer tape to hold one piece
against the other. In each case, I had a slight (maybe 5 to 10 mils
or so) gap in the seam. I finally used the old "many clamps" method
and just glued the last veneer piece to the substrate without heat.
That worked just fine. No gaps. I assume that the wood pieces lost
moisture when heated and shrank leaving the gap.
Does the problem go away if the veneer is very thin, or is there
another way to eliminate this gap problem.
I haven't done it myself but I often see the veneering guys using
super glue (cyanoacrylate (sp?)). Gluing the edges together first.
Small amounts cyano with just a little pressure instantly cure to a
very strong bond. Too much glue won't let the catalyst process heat up
enough form the pressure to bond; so thin applications.
Just an idea.
I usually use a plastic glue (unibond, but there are others) that
dries hard as a rock. PVA will creep under continued stress and is no
match for shrinking wood. I presume that thinner veneer would be
easier to control.
The problem may be that the heat expands the veneer, then when it cools and
contracts, it forms a gap. May be much less a problem with thin veneer that
doesn't take nearly as much heat to bond the PVA. Not that I've ever done
If you are using relatively narrow pieces of veneer to cover a wider
surface you first make all the veneer pieces into one. You do that by
joining mating edges then laying them out and fastening them together
with veneer tape on the top surfaces (veneer tape is paper with
mucilage on the back - some has holes, some doesn't, with holes is
easier to remove). Strips of masking tape pulled tightly across the
joint will pull them together while the veneer tape dries and keeps
the top surfaces flush.
Once the tape dries, bend open the joints and coat with white glue.
Bend back, wipe off squeeze out and let dry. Again, strips of masking
tape across the joints can provide lateral pressure if needed. Once
the glue dries remove any masking tape.
You now have a wide piece of veneer. If the veneer sheet is NOT flat,
you need to make it so. I'll leave that for you to research (hint:
Constatine's). If it IS flat, it is ready to glue to the substrate
but I would NOT try to iron it on...especially one as thick as yours.
Ironing (max heat) works fine for edging though.
The usual ways of gluing down the veneer sheet are vacuum press,
veneer press, cauls, contact cement. If it is narrow enough you can
just put a piece of 3/4 ply on top and edge clamp it. Here is another
possible way for wider veneers. I have not tried it but intend to do
so. I have used it in other applications.
1. Center sub-strate on a piece of 3/4 ply about 1-2"" wider on all
sides than sub-strate
2. Apply glue to sub-strate
3. Position veneer on sub-strate
4. Cover veneer with protective paper such as brown wrapping paper
5. Put a piece of thick foam rubber same size as ply bottom on top of
6. Put another piece of 3/4" ply same size as bottom on top of paper
7. Edge clamp ply to ply all around.
The problem with wide veneers is getting pressure on the center of the
veneer. I think the above would do so due to the foam rubber.
Regardless of how the veneer is attached, once it is dry you have to
remove the veneer tape. You do so by moistening it, scraping it up
then wetting & wiping off any residual mucilage. After sanding, you
are ready to finish.
I'm thinking your veneer is too thick for this method to work well. The
amount of heat needed to activate the glue is expanding the veneer. When
it cools off and contracts, something has to give and the seem opens up.
This (Amazon.com product link shortened) />/
has multiple articles referencing this iron-on veneering method. A
couple comments that might be relevant: a) some woods shrink under the
heat, pre-shrink (heat) the veneers before applying. b) leave a small
overlap when gluing down the middle of the "next" individual veneer
piece, then trim and/or press down the edge of this piece that mates
with a previous piece in a "second pass".
As other have mentioned, this would probably work better with thinner
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