Hi,

I've got a nasty blackberry bramble to get rid of. It's so nasty a goat hanged itself in there. Herbicides like to use a surfactant, and I'm wondering if either the glycerine bi-product or the soapy biodiesel itself might be suitable to mix with a water-based herbicide?

The glycerin itself is a surfactant.
NaOH based glycerin might help to "burn" out the plant.
You may want to fully saponify the glycerin as there are still saponifiable elements within the glycerin.

I would say try it both ways and see.

Let us know the results!

If you are still using water the first wash water will get things started and then use your glycerine, methnaol still init, diluted to very runy and give it a good dose.I am assuming NaOH as the caustic. The above combination will kill anything green. I inadvertantly did in a full grown pine tree this way.Dumb and stupid, but then experience is the best education.

Good point on the water Legal!

My driveway has been weed free since I started with biodiesel.