I think when professional armatures are being used P.T.F.E plumbers tape is used, it allows for movement on the joints also it stops any reation between the plasticine and the armature, conty's on the right track I have used masking tape before which does stick well to plasticine.
You can get masking and P.T.F.E tape From most DIY centres
ahh thanks cavor, i didnt realise there was proper stuff to use, il get some, thanks, oohh my uncles a plummer maybe he might have some in his plummers bag!!!!