Terrarium background help?

Ok so i built two differnt backgrounds and have a few differn't questions. Ok so my first one, i used spraypaint to one both backgrounds, how long should i let it air out before puting it in the cage. On the other background i tried glueing dirt on to make it texturized. it didn't work so i used a differnt spraypaint and woops i forgot to check if it disolves stierfoam so now everywhere there is no dirt its really crappy (which is only in a few places) any way i can save it?