Yesterday I refinished a large part of my kitchen wall with "smart non-shrink wall fix" (zero VOC). It was harder to apply than the plain old wall fix I usually use, so I left it more rough and thick than I normally would, figuring that spackling is easy to sand so my usual perfectionsm wasn't necessary anyway. This evening I started to sand it. Well, started to TRY to sand it! It has dried to a strange rubbery consistency. Reading the back of the tub, it says "requires no sanding" and, under the warnings, there's the usual cautions about sanding causing dust. It doesn't say anywhere that it cannot be sanded, or that it is supposed to dry rubbery. Any ideas on what might have gone wrong, and how I can get the horrible stuff off my wall so I can start over, would be gratefully received. Thanks