Pond Boss Forums GENERAL QUESTIONS Product sources need product for sealing surface rust on culvert

That's what it appears this flex seal stuff is. Rubberized automotive undercoating.

Could not find a MSDS on it, so no way to tell what's really up with it.

Go to any auto parts store and pick it up quite a bit cheaper.

I am not actually advising you to do this, as a fix for your problem.