What is a 'canvas strainer'. Is Mighty Muck the same type of adhesive as Yes Paste? Masonite is a good material to use? Not quite acid free.
Don't know what the strainer is... but...
Masonite isn't acid free, correct. I just took my PH pen and rubbed it on and it came out Yellow (acidic) Archival, I'd guess you'd have to use Sintra, which would be just like Masonite and comes in 3mm and 6mm thicknesses, possibly more. I think PiedmontPLastics.com carries it, if not, just search google for Sintra Mounting Board.
A note about Masonite.. some album MFG's like Zookbinders use it for their covers. Now, the covers only really touch leather... but you would think if they use it, they would had tested it to know what was good/bad. Maybe they know something about Masonite we don't?