Advice Needed: Making Double-thickness Mountboard

[prospero]

My first thought would be to turn the join into a "feature" and not try to disguise it. Perhaps using a third board with a different coloured core and creating a sandwich. The join between each board would be visible but not obvious. A black core board in the middle could look stunning and certainly different. Can't speak from experience and this might be total carp but who knows

I have done this in the past by using a bright red paper in the middle of the sandwich. Also mounting two layers of contrasting coloured papers on the top of a board. The effect is very pleasing. But having said that, it's sort of thing you do out of curiosity, stand back and say, "OOOOO! That looks good!" And then never use it again.

[JFeig]

A point to remember,

All board manufacturers are technically "converters".... that is, they assembly the boards from layers of paper. This is done with at least 2 types of adhesive - a vegetable based adhesive (wheat/rice paste , dextrene[corn] based products.... & methyl cellulose based adhesives). They also sometimes use chemical based adhesives.

[prospero]

Hence the (archaic) terms, 2-sheet, 4-sheet, 6-sheet, etc, to denote thickness.

[Roboframer]

I wanna sheet ona da bed.