On Sunday, 17 February 2019 09:27:55 UTC, wrote:
I have some old Creosote, for treating wooden fencing. It has become quite thick because most of the paraffin solvent has evaporated. I've been trying, unsuccessfully to mix in paraffin in an attempt to thin it.
Please, can anyone advise me on how to add paraffin, or old engine oil, to old creosote?

Some "creosote" (creocote) is water based.
See if your brush washes out with water to find out.
If so, you can thin it with water.
It's not as good as the old stuff.