I'm creating a wall using some stones I made recently. Using individuall stones rises the level of realism and gives you almost endless possibilities when building. I've created two test pieces of a simple wall. One piece consists of stones just glued together using pva glue, the other one has gaps between rocks to add mortar. Here's a picture showing the second version:

I'm thinking of a way to add mortar to make it even more realistic. I came up with two options:
- use wall spackle, which means I would have to mask all the stones with masking tape, cause wall spackle tends to get on everything and covers all the details
- use green stuff (modelling putty), just roll tine pieces of it and fill the gaps, which is easier than wall spackle
I will try to make some small test pieces to try those two techniques. In the mean time I would like to ask you if you know any techniques of adding mortar?? What would you suggest to make it look realistic? Any and all comments are more than welcome. Thanks in advance for your help,
cheers,
dsc.