_Generally_, the pre-heat step to dry everything out was important for
fiber-based prints and cardboard type mounting board. If the materials
weren't suffiently dried, the finished mount could warp. I would think that
this is not as important with RC prints and foamboard, since both are not as
likely to retain moisture/humidity. OTOH, it probably wouldn't hurt, except
perhaps to "soften" the RC paper surface if it gets too hot.

I've never had problems with air bubbles trapped under the print, but the
tiniest bit of dust can make a bump on the print surface. Does your air
bubble have a smooth dome-like appearence, or is there a "point" bump?
Cleanliness is just as important around the dry-mount press as elsewhere in
the darkroom.

I mount a lot of prints on foamcore, using a spray adhesive (Duro
All-Purpose Spray Adhesive, available at WalMart), and the heated dry mount
press to "set" the adhesive.

You are using a mounting tissue/film designed for RC paper, and being
careful with the press temperature, right? Too hot, and you can have a real
mess on your hands, actually on your press.

Ken Hart

foamboard?!

ive never tried that but if its what im thinking of,
the typical foam board is paper with foam sandwiched between,
as long as the print is dry you should be ok, the bubbles would be
my guess that something expanded in the foam due to the temperature.

k

More than likely dirt or dust between the print, the tissue or the matteboard.
Don't use foamcore "unless it is" acid free. Regular Foamcore turns yellow in
time (It has alot of acid in it).

RC prints don't retain moisture so that is not the issue here, however it
doesn't hurt to dry out/preheat  the mount, even foamcore has paper surfaces
and (if your humidity is high) that may be the issue.  Additionally if the
mount is preheated the press will not have to heat print, mounting tissue
AND mount when you put your assembly in the press.

On the other hand, you can also get bubbles if your press temp is too low or
if you are trying to use a FB type tissue with RC prints (e.g. Seal MT5).
The temp required for MT5 to bond well approaches the melting temp of RC
prints so you may not be getting a good bond.

With conventional FB prints it's always a good idea to preheat each piece
since you can actually get steam forming little bubbles under the print.

I've read all the very good replies to your request here and I can
share what I learned in college as I majored in fine art photography.

Now keep in mind I'm just sharing what my dept. head taught us.

First, we NEVER were allowed to use foam-core board in the heat press,
ever or he'd hack our fingers off. It is possible that the heat press
is heating the foam and it's sinking inward. Do a test on just the
foam and observe it. We were only allowed to use spray adhesive on
foam- core.

For dry mounting we used the appropriate dry mount sheet for the
paper, adjusted the temp appropriately for the paper (RC will be
different than fiber based) and only used a clean press and archival
matt board, but we first lined up the print with diagrams and used a
tacking iron to first tack it to the back of the print and then lift
it up and tack it to the board, then used thick paper top and bottom
and pressed it in.

As well, all prints must be air dried or pushed through the dryer
beforehand.

Hope that helps! Good luck.