it has been years since I have build one. obviously things have changed as well as techniques.
what type of putty is used for mortor with out cracking?
A: Millput (brand name of 2 part epoxy) will not crack & is extremely strong. I have used tile grout on the back of a tile with excellent results, just know once it is set there is no going back without a carbide drill bit or a grinder. Others have used various material like Celluclay with good results.
where do I get cork sheets from?
A: Cork board from dollar store? Model RR have the lengths for track bed.
which is better plaster of paris or hydrocal?
A: Never worked with either so cannot help.
can oil paints be thinned to be spray with an airbrush?
A: If it can be thinned it can be sprayed, most use oil paints for detail painting like faces and weathering washes for armor. I do not use a airbrush so sorry no definitive answer for that one.
thank you