Do the bowls come out of the mold? Are they cracked? You are leaving the mix in the molds to cure for too long before unmolding. A chip bowl (I'm assuming potato chip) isn't that big and you can unmold in 24 hours. Sometimes a vacuum can form so the piece is hard to remove. Either drill a small hole in the bottom or wrap the outside of the mold with warm towels. I've been known to pound and bounce on the ground some of my molds to release a pot. Most of the time though the pot slides right out.
Are the sides of the mold (chip bowl) smooth or is there a design?
Quote "The texture also doesn't look right, it's much rougher (before brushing) than most of the pictures I've seen." The bowls or the stepping stones texture? You're just saying you used quick-set concrete for the stepping stones. Is that the recipe you're using for the stepping stones, just quickset concrete? Billie

Thanks, I'll try again with a shorter time to set.

I wasn't able to get either bowl to let go of the hypertufa without breaking it into pieces. Both bowls are smooth on the side with the hypertufa, as was the nursery pot.

It's the texture of the hypertufa that looks wrong. It's rough and lumpy, even on the side I was able to get away from the smooth mold. At one point I hoped I didn't have enough water, but that wouldn't sit on the mold.

The stepping stones have come out pretty well, I wasn't going for any particular texture, I just wanted to see if I could make some design-free stones for my yard cheaply. I mostly mentioned it as a project that had gone well, in case there was a lesson to be learned from that success.

Are you getting the turfa mixed well if it us rough and lumpy? I compare what I use to the consistency of mushy meatloaf. But I wouldn't think it would have anything to do with release. Giving Billie credit, she makes hamburger or hot dog shapes and then applies to the side of the mold. You have to squish the patties together so you don't have gaps but I have found that it makes it alot easier. Helps with thickness and seems to go faster. I mostly use a plastic shopping bag for release. But it does leave marks where the bag is and will leave color if you happen to forget to use the inside. I tried to make some lids for pots and had a horrible time. Finally used a bag. Maybe if you start with a bag and move on to the spray. I have some sm POP molds I made and I use petroleum jelly on them that I spread with my finger and that works for me but that would be a pain for something bigger. Good Luck. Keep us posted on your next project. Kathy S

If the molds are smooth and you oiled them you shouldn't have a problem unmolding them unless it's a vacuum problem. Then the small drilled hole or warm towel will break the vacuum.
How thick are the walls on your hypertufa pieces?
You usually only need a thin coating of oil for a release, try using a little more than what you've been using.
Peat moss has to be smoothed out, no big lumps. You can break it apart with your hands or put it through a sieve. Same goes for perlite.
You combine and mix all dry ingredients until you have a consistant color before you add the water.

You shouldn't be having that much trouble...

Is there some kind of edge that could be gripping the concrete? If there is a depression or recess that the mix is hardening inside of, it will grip the bowl and not let you release it. Something as simple and shallow as the dimples in a golf ball will prevent the concrete from turning loose.

Look for a depression or a ridge that could be causing the problem.

Otherwise, just get a plain, smooth bowl from a thrift shop or a dollar store, and try again. If it works okay, it is the design and not your recipe.

Look at the link below -- even the shallow dimples in that bowl will prevent unmolding.

Sue

Here is a link that might be useful: Depressions can be trouble

Hi:

Are your bowls straight sided and/or rigid? It is virtually impossible to get something out of a mold with verticle, rigid sides if those sides are not made to release (made in two pieces, or with a hinge, etc.). If not, drill a hole to break the vacuum like Billie said. Also, I have had luck putting the whole thing into a vat of hot water to get the planter to release. Sometimes it is easier to just line the mold with an old plastic bag to ensure that you can get the trough out -- nothing more annoying than making a nice trough and then having to break it 'cause it won't come out of the blasted mold :>)

A few thoughts
If your having trouble using a release agent like spray oil, maybe try a dry cleaner bag between the container and the tufa. Not my favorite but it will work.
Also temperature may be a cause of the cracking. Maybe bring into the warmer part of your house. The unheated garage was definitely too cold - At low temperatures hydration occurs very slowly. Consequently, low ambient temperatures retard set time and strength gain of concrete.
My guess is if you try making tufa in the spring when the temps are warmer you will not have as much difficulty with cracking.

My first experiments with making tufa was in the winter months and they all cracked either initially or over time

Mike

Thanks for the suggestions everyone, I've had some success of late with unmolding thanks to all of you.

The first bowl I was using was totally smooth. Warming it up seemed to help. I still had to work to get it out, but this one came out in one piece.

When I try to form a 'tufa container from the outside of the mold, I still have some trouble because the 'tufa makes a seal with the edge of the mold from sitting upside down. I think a little practice will fix that.

However, I also want to make some large containers with 'tufa and gravity seems to work against me there. Once it gets so high (especially when I've lined my mold with plastic) the 'tufa just slides to the bottom. I've been thinking of doing a project in phases  put some 'tufa on the bottom of the mold and give it some time to set before I add more above it. Is there a better way to deal with the problem?

Then again, I haven't seen many tall hypertufa projects (aside from some spheres) is that something ill-suited for 'tufa?

How wet is your tufa? It usually doesn't slide unless it's too wet, so that the base can't hold and it "slumps" down. I'm assuming you're forming on the inside of a mold, so just make sure to keep everything good and compressed as you work up to the top. Remember, bottom of the sides has to be able to support the weight of what's put on it.

Yes, too much water in the mix will cause slumping. First, add just enough water to moisten the mix, and when that has been evenly distributed, add more water, a small amount at a time. It's funny how fast it can change from too dry to too wet! The closer you get to the ideal, reduce the amount of water you're adding -- I've had to add it literally by the spoonful at a time to get the mix I wanted.

Yes, doing it in layers is possible, and for some things, the only way (like spheres).

The best way is to do the bottom section, and let it sit just until it's set (approx. and hour or so), then add your next layer and repeat. If you let it go too long (to the point where the concrete looks a bit dryish), spritz it with some water and let it soak in, then add your next layer.

If you have to let the previous layer set longer (yes, I guess you have to stop to take the kid to the ER!), soak it good with water and drain, then apply the next layer while it's still wet.

If the concrete is fastening around the edge of the mold, when the mix has set fairly well, to the point you can pick it up and turn it over, scrape the edge with a putty knife. At that point, it should be fairly easy to remove. And it usually gives a good clean finish, too.

Sue