by TimC » Sat Mar 12, 2022 7:47 pm
Depending on your plan about diluting TBII I would say you need a gallon. 16 oz bottles are also available so pick one up just in case and you'll be golden. If you want to spread it full strength then I can't really say. I don't prescribe to that method.
On our last job (5x8 foamie, roof, hatch and exterior walls) we cut it about 50% glue 50% lukewarm water (it was a hot sunny day and the process became tacky quite quickly). One coat on the scratched foam and three conservative coats after the canvas was applied and the previous coat was still tacky. YMMV. We used two gallons total; it was used extensively in the construction.