If it's white or cream in colour, it's probably a 2 part polyester filler like you'd use on car bodywork. There aren't really any other fillers you could use to do it with. Old style cellulose filler could do it, but would take months to dry and would crack if rushed. It would be really heavy it had been built up with fillets of braze.
If it's white or cream in colour, it's probably a 2 part polyester filler like you'd use on car bodywork. There aren't really any other fillers you could use to do it with. Old style cellulose filler could do it, but would take months to dry and would crack if rushed. It would be really heavy it had been built up with fillets of braze.