I have weighted several dishes like 1,8m Andrew and Prodelin, they weight about 35kg (no mount included). However, there are another models of same size dishes, and they can weight about 10kg. So, to answer the origuinal question, I would say, that for 1,6m dish, about 10kg of resin is needed..... depending on the design.
adding to what
@RimaNTSS and
@battenfan writes, the dishes that are around 35 kg (as my Channel Master 180) are self-carrying fibre-reinforced plastic designs where the structure of the dish keeps and carries the shape even under strong wind-loadings.
This is the commercially most efficient, as the dishes are cheaper to manufacture and especially ship than alternatives.
One of the alternatives is to made a comparatively thin reflector, and get the rigidity and shape by bolting it onto an iron frame.
There's a thread here
Newbie Here - Elevation help needed for 1.8m offset dish (Malta) with pictures of a CM180 clone, which is made by molding resin (I believe it was) over a real CM180, and then fitting this onto a metal frame.
If you don't have a CM180 or similar offset dish handy as a mold, I suggest you try and make a prime focus dish instead as discussed above. This make the profile easier to obtain, as it is symmetric around the central axis. You can even make the mold from clay/soil, as demonstrated on certain African websites.
If you just want to experiment before you start pouring resin, you can even start out by making a full size test-bed with wooden parts (ribs, centre hub, edge struts), and build a surface on the clay mold using paper mache (glue, water & newspaper) and kitchen foil in a couple of layers as reflector.
This won't tolerate rain or any kind of wind, but this could get you started with geometry etc.