Oh oh...finally something I know a little bit about! :)
First...it is possible your mix from freesycle was bad...the cement in the mix can go bad if it has been exposed to too much moisture.
Second...you might have had too much water if it ended up slumping like that. You might consider wrapping the glass in wire mesh or paper mache. Not sure how the other gal did it...hopefully she will chime in here.

You can sift out the rocks and still use what's left...it will work if the cement is good. It sounds like what you have is "quickcrete" or "sacrete" where the cement is already mixed with gravel.
"Cement" is the very fine gray powdery stuff that you mix with an agragate such as sand or gravel (you can even yse peat moss) and then mix with water to make "concrete". I use portland cement and mix it with sand and water...there are actually many recipes for these types of projects. You can get a LOT of info in the Garden Junk or Hypertufa forum.
I know others on here have worked with cement, also and will have some very good advice. Dont give up on it...it's fun working with cement when you get the hang of it! I am still learning!

Good luck...look forward to seeing your mushroom!

Crystal

Hi Pat! Sorry to hear what happened. I think it might be because of the rocks in your mix. I really don't know if your idea of taking the rocks out of the mix and trying again would work or not. If you do try that, maybe add some sand, too? Maybe Klinger can chime in here, she definitely would know better than me!

I used a mix of 1 part portland cement, 3 parts sand, and less than 1 part water. You had the right idea about making the mix as "dry" as possible.

You asked what the difference is between cement and concrete....that was so hard for me to keep straight - but I think I finally understand it. Cement is an INGREDIENT of concrete. Concrete is the mixture of portland cement, various aggregates (sand or rocks, etc) and water.

Good luck!

you know, I've been wondering about using those bud vases (for mushroom stems) in a different way, and wondering if it would work. I have a feeling it might NOT....but thought I'd throw out the idea - what if we put the concrete mix INSIDE the bud vase and then after it hardens, break the bud vase - like Klinger does with the glass globes?? The reason I think it might NOT work, is that most of the bud vases I find are a pretty thick glass, and I'm not sure how they would break - maybe if we were lucky enough to find a bud vase made with a thin glass?

"Things that make you go Hmmmmm"!

concrete with aggregate(the rocks) is great for casting stepping stones. p

Hi, I think a couple of things happened here. The mix you have is a combination of portland cement, sand and small rocks. I is designed to be a strong mix and would be very good the way it is for stepping stones, as pea mentioned. You can sift the rocks out and use it for your mushroom, but don't add more sand, that will weaken the mix as the ratios would change.I think your mix slumped for two reasons. First it didn't have much to grab onto as the bud vase would be slippery, second the mix may have been to watery. What I'd suggest is you put something on your bud vase to give the mix something to grab a hold of. Some screen, mesh , I think drywall mesh would work well. Then the mix will have something to bite into and grab a hold of. Then apply a thin coating of mix, you may have gone to thick initially. When it is cured you can wet it down and add a second coating. The weight of a thick coating will pull it down . If you've got a larger bud base you could for sure fill it and break it. It would be heavier being solid concrete but that probably isn't a big deal. Hope this helps,
Cindy