Tim Watts wrote:

I saw some discs in Alsford Timber the other day that were available in
9" and 12" (might have been a 4-odd inch too) that were advertised for
wood, especially tree roots. They had some almighty lumps (1/8-1/4") of
abrasive (maybe carbide) suck on the side. Looked bloody viscous

You definitely want a low-viscosity blade.