Grout on shower base

I had some tile installed in a shower, and while the tile work is fine, there's dried grout on the shower base.

Any ideas on how to clean it off without ruining the (plastic) base? The base is textured, if that makes a difference.

Assuming it is a cement based grout, try some plain vinegar...it will disolve the calcium. Limeaway may do it. This shouldn't hurt a plastic base, but check the manufacturer's cautions or warnings to see if a mild acid is a problem. If it is a sanded grout, be careful about rubbing...the sand you wash out will scratch the plastic. Maybe take a paper towel, saturate it with the liquid and let it sit overnight covered with some plastic so it doesn't evaporate. I do that if I didn't clean my mixing bucket really well. I'll have a slurry of sand and cement particles by morning.