stain removal

Hi there, would really appreciate some advice on how to clean diluted pollyfiller from my wall (a plasterer washed his bucket out and it splashed against the wall and he refuses to clean it). The house was built in 1986 and I assume it's reconstituted or cast stone but I'm not certain. Have...

Can anyone recommend any products they have used to successfully get rid of black staining on stone? I think it's black mold and Google results tell me to use bleach and a scrubbing brush but I'm hesitant on using any bleach. Any tips would be greatly appreciated!