Hi Kathy,

I'm a newbie myself, but I have a guess. If you used concrete instead of cement, your mixture was too weak to hold together. Concrete is cement mixed with other stuff.

The usual "recipe" for concrete is 1 part cement to 2 parts sand and 3 parts aggregate. So when you buy concrete in the bag, the cement is already diluted 5 to 1 because it's meant to be ready to use by just adding water. Adding peat and perlite to that dilutes it even more. Since the cement is what holds everything together, that means your pieces will very lack the strength they need to last.

If you buy straight Portland cement instead of concrete, you can control the proportions of your mix to keep its strength. I've been using roughly one part cement to one part each of sand, perlite, vermiculite, and peat. I haven't been at it long enough to overwinter anything yet, but so far everything's nice and strong.

Hope that helps!
LadyLong

thank you LadyLong,

I just don't like buying all those different things so thought it would be easier to just buy the mix that you just add water to. Then, of course, I added more stuff! I don't have the room to store all those different bags of things. Is there any way I can use that mix and make it work?

Kathy

The important "trick" or "secret" is in that Portland cement. I appreciate the difficulty because it only comes in 90 pound bags where I can buy it. I've been talking these projects up and hope to get a mud-buddy so we can work together (help lift, etc.) and split costs and quantities. So far, I'm a loner.

Two considerations: be careful how "wet" you make your mix. Too much water = weakness. Also, buy a little bag of polyester fibers (about $5 at HD or Lowes). You only need to add a small quantity and it may really help. You might want to look at a few concrete web sites. Try "papercrete" in Google for a better understanding of how Portland cement works with fibers and aggregate to make the object.

David

Kathie,

A contractors or garbage compactor plastic garbage sacks inside a Rubbermaid lidded garbage can or lidded tub will store the Portland cement safely for a really long time (in my case, years). You can store it outdoors or in the basement or garage. Rubbermaid holds up the best, in my experience; some of the other brands crumble and break within a year, especially when exposed to UV light.

I think it's worth it to get the white Portland cement just because it is so versatile.

If you use PVA fibers instead of nylon or polyester fibers, don't use admix because that could interfer with the cement-PVA bond.

Hey, Tufftufa -- I've looked at both HD and Lowe's (several of each) and haven't been able to find the fibers. Are they in a secret place? What should I be looking for?