They are still soft when I poke them to test them. I unmolded one and it retained its shape, but the hypertufa is still crumbly, not all that different from when I made them last weekend.

There could be several reason for you problem.

Was this your first attempt at making hypertufa? Were you sucessful with other projects?

I use a different formula. I use 1 - 1 - 1 Portland Cement , Peat, Perlite. Consider doing a batch with this mix and see if you have the same problem. There could be some other things that could casue you problem.

The potland cement should be fresh, ( keep in a sealed container between projects) If it was old portland cement it will cause problems with the curing process.

Peat should be damp, ( too dry and it may not absord water well). Since you used perlite and vermiculite, I am not sure if this would be an issue.

Mix all dry ingredients well before you add water. ( this help with spreading the portland to all surfaces of the other incredients - good bond) Then slowly add water until it all evenly moist. Make a ball of the mix - squeeze until it drips water slightly. ( too dry and it may crumble as it cures) Too wet could also be a probelm with the curing process. It is possible that if yours was "crumbly" when you first made your mushrooms, that it may have been too dry. I liked the wet mix to making a meatloaf. It should all stick together!

Please Post a photo, it will help. On my site ( on the right side) there is a "how to make hypertufa" page that I put together with more details - may help.

Instructions on my blog

Did you use Portland cement or concrete mix or mortar mix for your third ingredient? Did you tamp the mix when you put it in the molds?

I had this problem earlier this year and had $400 of pots not set -- not a happy camper. This had never happened and I've been able to make hypertufa in my sleep since the very first trough and they came out just fine.

Initially, I thought that the Portland had expired as it does have a shelf life. Then I tried making something with Portland and sand and it set, so I then knew it wasn't the Portland.

What happened is that the peat moss was sooooo dry it sucked the moisture away from the Portland so that the Portland could not properly set. So, next batch I made sure it was not only properly hydrated but made the mixture, let it sit for about 15 minutes and then added more water.

This is all extremely helpful! Sounds as though I needed to get my peat damp first, then make my mixture, then let it sit. I'll get some more peat and start over. Thank you!!!