Keep applying layers of
latex until you build up a thick rubber mold. Always let the latex dry
completely before applying the next layer. After 5 or 6 layers start to fill in
between the cars.
In larger scales you may
want to add layers of medical gauze to stiffen up the mold. Just apply a layer
of latex then push the gauze on, and finish with another coat of latex. These
steps will require extra drying time.
I also have used bread
bag twist ties to make a mold somewhat bendable, like the old Gumby
and Pokey toys from the Howdy Doody
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