Hi Poakyl, I had no idea what this was so I did a search and found this posting from 2005 as well as many others. The board is slow this time of year but hopefully someone will come on that works with armatures. I haven't tried armatures. Good Luck.

youPosted by rickharmer z4British Colum (My Page) on Tue, Sep 6, 05 at 13:11

Hi,Bonnie.I've tried a formula that works so far.I use 1:1 portland and silica flour(available at pottery stores as silica sand,say 200 mesh),I also add a few fibres, a small portion of silica fume(check with concrete supply companies,not HD or lowes)and a very small portion of plasticizer(your choice on that one),and use only admix,no water.This mix is VERY sticky,but it seems to work.I've noticed that the piece is still together,but some minor cracking has occurred,probably due to my dropping it repeatedly on a concrete floor,which I doubt would occur in the home!I did no curing whatsoever,I was just playin'around.I'm busy on another piece at this time,so I won't get back to this for a while.I'll use the same mix as I described,but lay on a couple of finishing coats(inside and outside the bowl)of 1:1 without the silica fume or plasticizer.I'd do this for colour variation(I prefer integral colours from Davis Colours,available at concrete suppliers)and then finish it with a series of sanding reductions.This gives it a hard natural shine that is bowling ball smooth.At least,that's what I think I'll do.I've had a request to do a septic tank cover to look like a rock.Here,you start with a hula hoop....
Cheers from here

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Poakyl, send me an email.

poaky1, I have run several test using silica fume and the data found on several sites seems to be accurate: to add silica fume in an amount exceeding 8% by weight doesn't present any additional advantage. I do find the surface to have a "sparkle" to it and it is certainly harder on my finishing tools. Anyway, I'd love to hear about your experiences with silica fume and maybe pictures when you get a finished item. Oh yeah, if that mix isn't sticky enough remember you can add fire clay in the same proportion.
Robert