I have done some portland & peat planters lately. Heavy while curing but as they dry out they will get lighter. I was beginning to wonder. Is your "cement" portland or a ready mixed cement? Can make a difference in the weight as the ready mixes have sand in them or some other form of aggregate.
Paws

I'm using Portland cement. Good to hear it will get lighter.

Kim, Depending on the size, you can unmold in 24-48 hours, clean it up (wire brush,carve,etc) GENTLY THIS IS STILL FRESH, spray with water and put back in a plastic bag in the shade for a couple of days, spray water inside the bag every day. Then place in a water bath (I use a plastic muck bucket or mortar pan) to finish cure and leach out the lime for a couple more days. For most troughs you can use in a week to a week and a half. Billie

Kim, I've made lots of troughs using the very same recipe (only doubled). You can generally unmold within 24-48 hours; I've gotten busy and forgotten about them for several days. Anyhow, just unmold, scrape like Billieann says and put them back in the bag. I've never waterbathed them (have to give that try), but stuck them in a shady spot, and hosed them off or left them full of water and hosed them every couple of days, and they cured just fine. Seems like everyone has their own method of curing...just don't rush the cure and you'll get a good, strong trough.

I'm starting to wonder if it can really be done! I tried five times and everything crumbles. I think I will give up on hypertufa and just use cement and sand.

Hi Claire
What did you do exactly?
What was your recipe? Is your Portland cement fresh?
There are a couple of things you can do to have almost fool proof results.
Peat is probably not the problem. I have stuff that is 80% peat and it is very strong.

Claire:
Don't give up!! You can do this...Tufa Enough is right -- what recipe are you using? Funny thing is, too much cement messes things up instead of making them stronger. One of the great features of hypertufa is that it weighs about 1/4 of what a pure concrete planter weighs, and if you just use cement and sand, it is going to be very heavy which defeats the whole purpose.