I have the pink foam glued to the plywood. Should I paint the foam with latex paint first or glue down the roadbed before painting? Also, I plan on using cheap latex caulk for attaching the roadbed to the pink foam. Is that okay?
Larry
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Larry,
I think the plywood will adhere better to the foam if you do not paint it first. Paint after you glue the plywood. Caulk will probably do, I used Elmer's white glue, it's cheaper if you buy it in the gallon size. It is good for many, many projects from ballasting to other scenicing projects.
Paul Edgar
Just a short note. Some have discussed forgetting to remove that thin clear plastic coating that is on some pink foam board before painting.
In keeping with Larry's post above......
In my experience it is wise to remove the polyethelene skin before painting the foam.
Thanks for the replies! I apologize for any confusion I caused. I have already glued the pink foam to the plywood. Now I am wondering what the next step should be. Paint the base coat of latex paint on the pink foam (which would be easy now with nothing on the foam) OR glue the roadbed to the pink foam. I wasn't sure if the roadbed glue would adhere to the dried latex paint. Would the roadbed glue stick to the pink foam better? Does it matter?
I am using the thin foam sill sealer as a roadbed for Fastrack. I checked for the clear plastic coating but this pink foam does not have it.
Again thanks for the replies!
Larry
If I could suggest that you paint a small extra piece and do a test. I have not used caulk to hold down any foam board painted but I have used all kinds of other adhesives, glues ect. I have never had a problem using them on painted foam board.
IMO it's all lot easier to paint first.
Larry,
"I wasn't sure if the roadbed glue would adhere to the dried latex paint. Would the roadbed glue stick to the pink foam better?"
In my experience, bare pink foam doesn't hold glue well, because it's so porous.The glue seeps away from the joint. Also, some adhesives contain chemicals that will attack the foam. Painting foam with flat latex gives it a skin so the glue stays put. I wouldn't hang from a girder made of it like on the old Krazy Glue ads, but the forces exerted on scenery are a little more modest. 
