Formatting for piano and voices

I'm trying to format a score for SATB with piano. I'd like the first four measures to be piano only, then add the SATB on top of the piano starting on the fifth measure. Then, I want to go back to just piano for another four measures at measure 37, then back to SATB and piano at measure 41 to the end. I cannot figure out how to get this format. I tried starting with SATB and piano and removing the voices, but it removed them for the entire piece. Then I tried adding them back in at measure 5 and they wouldn't add above the piano line, plus I kept getting doubles of each voice. I'm confused!