Fire retardants and modern marouflage

I am currently reviewing a project proposal where complete
replacement of a decorative scheme painted on a large groin-vaulted
ceiling is necessary.  The firm proposes to paint onto canvas and
install canvas into the vault cells using adhesives--primarily as a
cost-saving technique (as opposed to painting directly onto the
plaster) but with the added benefits of stabilizing the plaster
during earthquakes and being removable for eventual substrate
repairs. The City requires that the canvas be treated with a Class A
fire-retardant and I am curious about the potential for chemical
reactivity within the proposed system--possibly at one or more of
the interfaces between substrate, adhesive, treated canvas and the
paint film system.

Through my own research and collegial inquiries:

I have found that proprietary fire retardants for canvas are largely
complex, soluble, ammonium salts.  Several muralists and mural
conservators have had success using the salts-treated canvas and
acrylic emulsion paint systems (as is proposed for this project)
with two differences--their examples were either stretcher-hung or
installed vertically on a wall, not upside-down, and another example
had only one side of the canvas salt-treated (verso) and used Beva
gel as the adhesive (clay-based adhesive proposed for this project).
Sunbrella-brand synthetic canvas was considered as a replacement for
the salts-treated cotton canvas but would seem to be too
adhesion-resistant ("too slick to stick," as one person put it).
Sunbrella-brand canvas is a Class A "self-extinguishing" material
with a fluorocarbon coating--the more one looks into it the more it
seems like a Teflon-type fabric.

Does anyone have more to add to this information? Anecdotal
information welcome--and has been quite helpful.

Molly Lambert
Architectural Conservation
San Francisco

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                  Conservation DistList Instance 12:81
                  Distributed: Tuesday, April 20, 1999
                       Message Id: cdl-12-81-019
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