Oh, I just loved using wood ash. It really made a nice color tufa, but it is so ssd to know it will all decay out someday. Here is a piece i made with the charcoal from our campfire last year. The ash is really good. It's nice and smooth and seems to be the perfect exotic ingredient. Didn't slow the cure, but back up on the peat.

Jo

Here is a link that might be useful: wood ash and charcoal

Hi Rick
I'm not sure you can get the ash clean enough.
The carbon will probably cause more problems than the ash will solve.
I don't even know how you can get the stuff under control.:)
Fly ash is hilarious to work with. I get more of it on me than in the mix.
BTW the concensus from concrete experts in my area is that fly ash and silica fume are wasted in Tufa or light weight concrete.
They work by making concrete extremely dense. If you use perlite or peat adding silica fume or ash won't do anything at all.
I see where they are coming from but I can find nothing on the net about this.