I have "vintage" concrete washtubs in my basement where I usually clean up fermenters/kegs and used star-san for the first time down there. After I dumped out the keg of star-san i wondered if the acid would do anything to the washtubs, acid etching, muriatic acid cleaning and all. It is a pretty weak mixture but just want to be sure it won't harm them.
I know, don't fear the foam.
I know, don't fear the foam.