Nevermind...

So 5 hours into it I have to admit defeat that my cunning plan is not going to work.

The chipboard, although possessing stupidly good shear strength has no compressive strength. Add to that the water is sucks out of the dental plaster and you effectively have a soggy green cardboard noodle. (The plaster is green.) If I get the plaster dry enough so it doesn't waterlog the paper it sets before I can position it, to wet and the paper melts.

Some of the first peices I did 5 hours ago are still soggy...

So looks like I will be going with my backup plan of a building suspension bridge instead of an arch bridge. Problem is for my suspended members the 176 1/8 thin paper strips are to thin to drill. I have an idea of cannibalizing the plastic moving totes that have broken as members. However, it being 10:30 at night I suspect my neighbors would frown on me using saw and dremel.

It will have to wait until tomorrow, but I think it will actually go faster then the arch bridge, as it is not unlike building a suit of scale armor...