Oil bonded sand is similar to Delft clay, but usually the sand is
foundry quality casting sand, and the grains are quite coarse.
Petrobond, and Petrobond II are additives to sand, for sand casting.
If you want to have a fairly grainy casting then buying oil bonded
sand would give you those results, and you can get a better price by
approaching a nonferrous metal foundry and asking if they can spare
a bucket of sand… I bought some and it cost me $30 for a 20kg
bucket of petrodond II oil bonded sand.
The casting lists I’m on are more DIY then I am, in that they like
to mull their own sand, but to do this you need a muller, and $30 is
Delft clay is a finer product and produces superior results to oil
bonded foundry sand.
You pay for fineness.
Kindest regards Charles A.