foam board has some unattractive chemistry. Its paper surfaces
are stiffened with urea formaldehyde, something not welcome in
preservation settings, while its foam is polystyrene, which can emit
styrene monomer, another questionable chemical. If an artist wants to
create a rigid support, options are open, which are not open to others,
but the adhesive and support must be chosen wisely.
dispersions are adhesive candidates, but they have low tack. One option
would be to apply gloss acrylic medium to the support and the back of
the watercolor and allow it to dry for 2 weeks. Then the surfactant
which has come out of the acrylic can be washed off with water and when
things are dry, the two surfaces can be bonded with heat. This will
create a permanent bond. Klucel G, hydroxypropyl cellulose can be mixed
(1 part HPC to 3-4 parts alcohol) with isopropyl alcohol to create a gel
which can be used as an adhesive. This should be soluble and
reversible, but it may not stick to all surfaces, and a layer of acrylic
medium (washed after 2 weeks) may be needed to prime the support
and Alucobond are Swiss made aluminum/polyethylene laminates, which can
be used as supports. If a water base adhesive is used, there may be
problems with the paper warping the support, so the Klucel G/ alcohol
has an advantage, here.
Other options are aluminum/polypropylene polyflute composite boards, which can be found at
LaminatorsInc.com under the names of D-lite = 3mil, Aluma-lite =4 mil, and Pro-lite = 10 mil.
A final possibility is the polypropylene honeycomb board made by Coroplast and sold as Stinger Board, which can be found at: Harbor Sales - 1000 Harbor Ct, Sudlersville, MD 21668.
The wisest play would be to laminate the watercolor paper, before creating the art, but if the adhesive is Klucel G. its reactivity to water may cause it to release, so it should be used after the painting is done.