Hello, I bought a 5 gallon bucket of sta-kool + 10 year elastometric white roof coating for $20.

I’m building a shed sided with hardie panel and roofed with corrugated metal. I bought this coating because I thought it was too good of a deal to pass up and I thought it might be nice to apply to the metal roof after I finished, for insulating and water proofing reasons. I recently saw a video warning against applying such coating to metal roofs though because it can bubble and crack creating a significant problem. So…I was thinking I can just use this coating as a wall paint on the hardie. Does anyone have experience or advice on whether or not this is a good idea? Thank you.