I'm taking flood is painting & then applying the vinyl. That's why I am in here. EXPERIENCE Talks! Doing yellow coro, mainly that it will just slide into the piece alot easier.
No, flooding is a silk screen process when you just usually screen print a full screen of one color with no image burnt on. It kinda floods the entire substrate, hence the term. In your case, this is far too big to use a screen, but I would still use yellow screener's ink for Cor-X and roll it on quickly. It's been my experience that screen printers ink will bite much better than regular paint. It will practically block out any light from the other side, which I now see isn't a factor, but good for you to know for future projects.
You could also buy some 48" or 60" yellow vinyl and just float that on as your background color and not need ink at all.
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Float': is a term we use when we use the wet method and soak the daylights out of the substrate and the back side of the vinyl when applying oversized panels and just squeegee the crap out of it once it's down until it lays flat. Let it dry thoroughly and then apply your graphics and/or copy.