are you putting them in a plastic bag? What recipe are you using?They need to be in a cool spot too and you should mist them every day for a week or so. They will lighten up after a couple weeks. I push my rocks and glass in right after I get them done before the bag. If they sink a little you can carve them out.

thx for your reply! i did wrap them in plastic bags and put them in my cool basement... but by the time i misted the next day they were so much harder than i anticipated! i will try again tomorrow, using your idea of mosaic-ing them right away. how long do you leave them in the mold? good to know the color will lighten!

I usually leave them in for 3-4 days just to be safe. I leave the bigger stuff in longer. Lots of trial and error. I do have a few broken things because I was impatient!! Good Luck!!!

It doesn't sound like it is hardening too fast.I've done a lot of mosaics in hypertufa and you really need to be inserting your pieces as soon as you finish making it. Your other alternative is to let it set up for at least a week and then adhere your pieces on top of your piece and grout them.

Wonder if the house/basement has the AC on or dehumidifier? it will take the moisture out of the hypertufa. Completely cover in a bag and tie the end. On day two open the bag and spray with water, same on day 3,4,5,6,7 continue to keep moist that way for about 1 week,
Leave them out side, they will be just find under a tree.
Place the rocks or whatever in the hypertufa when you are making the stepping stone.

i think i've correctly followed a recipe and instructions. If you are not sure, --- What did you do? Describe