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

Rick,

I have found your information and work very interesting. I have three quick questions:

1. what are you sanding your balls with? I am using a similar mix and want to get a smooth finish.

2. Is Handy Sand from Menards the same as silica sand? it is very fine and white.

3. Where is everyone getting these fibres? I have looked at H.D., Lowe's and others and cannot find them.

Thanks in advance for your help. Mary

Hi,Mary.I don't know what Handy Sand is.I get my "flour"like sand from a pottery store in Richmond,BC.It's from U.S. Silica under their trade name of "Sil-co-Sil".I'm fortunate to have a few places to get my fibres in the Vancouver area.I get Harbourite from a stucco company.you could do a Google search to find the nearest outlet for them.I just got glass,not fibreglass, fibres from a supplier in Maple Ridge,BC and she'll ship small amounts.
As to the finish-I've done several orbs at this point and I've only reduced(sanded)on one small one.It's a fair crack of work!I've left the others in a rougher state.I use a paintbrush to finish my current crop,but,I am going to try a smooth coat and also use a stiff scrub brush for another texture.
Good luck in your future work!!
Cheers from here

Thanks, Rick! You are always a big help. I have tried using quickwall as a finishing coat on one of my orbs and it makes a really smooth surface if you pat it after it sits for a minute or two. It's nice but I let it sit too long and now sanding is difficult. Luckily it is so smooth I may be able to use it as is.I have one idea nefore I give up on it: I am going to try my DH's orbital sander before he gets home from work ;)

Mary, if your husband has a hand grinder, use it instead of the orbital sander. There are sanding disk that you can get for it from course to very fine. It makes short work of very hard materials.