Homebrew PCBs

Hello all,

  I just want to confirm my understanding of using plumbers solder paste.

  I beleive people are using it to tin their board before populating, 
and use several thin layers of paste to completely tin a PCB.    Does 
anyone use this paste for SMD soldering?? What about down to 0.5mm pitch??

  I am just about to try my first SMD board, with parts down to 0.5mm 
and given that electronic soler paste has a very limited shelf life and 
the infrequent use I will have for it if I have to use regular paste for 
SMD work I may as well use it for tinining as well.

  BTW, I've run a test reflow following an 'average' profile to 225C 
using a skillet style (see sparkfun.com) of setup, unetched board and 
regular paste which was best before end 2003.  The paste formed a crusty 
grey coating over nicely tinned copper.  It almost looks like a nasty 
dry joint. If  you scrape the crust off the solder there is a nice shiny 
tinned copper surface, I've tried several different types of solvent but 
nothing seems to dissolve it.  Any ideas of what this is and how to get 
rid of it????  and before you flame me over the use of the very out of 
date paste, I knew it was out of date & I just wanted to see if the 
reflow profile worked on a scrap piece of PCB.

Thanks heaps

Trevor