Hi, a while ago i bought some ready mixed plaster from B&Q to use instead of filler. Recently, it ran out, so i bought some thistle one coat plaster from B&Q. I cleaned the bucket that the old plaster was in and mixed the new one. I applied my first layer and put the lid back on the bucket for the night. I have now come and found what seems like the whole thing gone solid. Is there any way I can recover this plaster????