Best way to remove cement from plasterboard?

[lognak]

Hello,
I have recently removed a decorative brick fire place surround and hearth. The surround was attached to the plasterboard with cement and metal ties. The ties have been removed and nearly all the cement has come off the plasterboard.
As we want to replace with a smaller surround there will be an area of the plasterboard visible with a small amount of cement. Whats the best way to remove?
Sand paper and/or water? anything other technique?
thanks

 

[dextrous]

Are you sure that it's cement?
Anyway, try a steam stripper on it- this shifts most types of adhesive eventually.

 

[dazdel]

Sure it's not grey finish plaster ?

 

[trowelmonkey1]

sounds odd this, can we have a pic?