This tape is used to cover the seams on vapour barriers in new houses....so maybe ask for that, if you cant find this brand??

Thanks Straw dog and Patio4! Exactly what I needed to know.

Another question: In their concrete isle (stocked mainly for building contractors) I also didn't see anything for reinforcement. Can anything be used? Wire? Cut up T-shirts? Etc.? Do I need to worry about organic additives rotting or degrading?

A few thoughts here:
Are you letting your 'tufa cure before removing it from the mold? Your 'tufa might be be too green to unmold. Rememember that cement mixtures have to cure, not dry (like POP) and the slower it cures the stronger it is.
Are you using a release agent on the molds? There are lots of them out there, I use Murphy's Oil Soap. You can also cover the bowl with plastic before applying the 'tufa. A garbage bag, plastic wrap, dry cleaner's bags, whatever you have on hand.
Are there any undercuts, tightly rolled or cut edges or those little plastic "fins" that stick out (I don't know how else to describe them) on your molds? Sometimes the cement mix grabs onto them just enough to cause breakage.
Perhaps you can give more detail on your trials and tribulations?

Quote: "I'm cracking bowls trying to take out the plastic form and saw a number of postings for Red Tuck Tape. My local Lowes is not familiar with it. Are you referring to red "duct" tape or red "Duck brand" tape?"
I'm not making the connection, what does tape and your pieces cracking have to do with each other? You want to tape your pieces back together?
Quote: "I also didn't see anything for reinforcement."
What are you trying to reinforce? What you use can depend on the project.
The only person that mentions using this tape has 50 aliases so maybe he'll be along to answer. Billie

Thanks all.

To bill anne, I mentioned the tuck tape because earlier posts
(See davidmcdn's post at http://forums2.gardenweb.com/forums/load/hypertufa/msg041400445519.html for example) recommended the product as a non-stick solution for releasing molds from castings.

I'm making 12 -14 inch bowls by turning the form upside down and packing the hypertufa on the outside. There are some "ledges" in the plastic bowl form, but they all are on the downside, meaning the casting should fall downward away from the ledge. There is also one fin, but it is at the lip of the bowl, and thus again the casting should drop down and away from it.

I could let it cure longer (I tried 24 hours last time) but I want it also to be green enough to carve and shape. I wondered if adding some sort of reinforment fibers would improve stability. One post (see packrat at http://forums2.gardenweb.com/forums/load/hypertufa/msg0520120815767.html) recommended unraveled braided poly rope mixed in the hypertufa and then burned off the outside. I didn't know if some light guage wire or maybe fabric strips could be laid into the casting to provide internal support and thus reduce cracking and breaking.

What are you using for molds, plastic? wood? metal? Are you using a release like a spray or covering the mold with plastic because you're working on the outside of the mold?
You shouldn't need reinforcement for a 12"-14" bowl unless the side walls are very thin or unusual shape/design.
You can unmold a 12"-14" bowl planter in 24 hours.
Since you're carving, it's to you're advantage to leave the mold in place as it will give you more stability. Billie

topnoggin, it sounds like undercuts may be your problem. Make sure you cut those fins out before you fill your mold--even with mold release those danged things will hang you up every time. Even if it seems like gravity should be pulling it out when you turn it upside-down. I've also had problems with suction not letting go of pieces. The thing that seems to work best for me, if I'm going to be carving a piece (because otherwise I leave it in the mold longer) is to line the mold with a dry cleaner bag. I'm going to be carving anyway, so lines won't be a problem, and I can smooth them out. Also, the extended bag gives me something to pull on, if need be. Something else I do is cast it extra thick. If I cast thinner than an inch, I'll break it for sure while I'm working on it. It's inevitable that I forget and grab the rim (a weak spot) while I'm carving and break it.

The weakness of green concrete is what makes it carveable so some compensations have to be made. Luckily that also makes it fixable. I make a slurry of portland and bonder/fortifier in a disposable cup and glue the pieces back together with it, pressing grains of what I've carved off into the crack to disguise it.

Hope this is helpful--let us know how it goes.

Deb

Here is a link that might be useful: Can you tell this was broken?

Thanks all.

This next weekend, I'm going to try again with Tuck Tape or a plastic bag over the plastic bowl to help it release.

Deb, your stuff is impressive. I'll see about getting some bonder/fortifier. Would Lowes/ Home Depot carry that or is it a specialty product? Also, to glue back together the bowl that broke about 2 weeks ago, would that slurry work or should I use the gorilla glue or morter mentioned in some of the other posts?

Topnoggin, thanks very much. Yes, you can get the bonder/fortifier at the box stores. I'm not 100% sure but if it broke a couple of weeks ago, it may be better to use the gorilla glue. You could try the slurry trick and if that didn't work, use gorilla glue.

Deb

PAM spray - I have been using since Billie Ann told me about it a few years ago - It works great on the inside of plastic bowls. Can pick up at dollar store for..... you guested it $1.
I am not sure how it works on other molds, but I can assure you I have never had a probelm getting tufa out since I began using it.

Thanks Billie Ann

Thanks everyone!

We have success! I used plastic and duct tape over the outside of the bowl and built the hypertufa on top of it. The bowl slipped out and the plastic peeled out.
It's about 8 inches across the bottom and about 14 inches across the top.
I found that the hypertufa followed gravity to the bottom of the mold (rim of the bowl), so the rim is thicker than the sides.
With the leftover hypertufa, I tried the same thing using a couple of plastic wrapped bricks. But I had to fight them out and the product broke. But the round ball came out all right. I used a cut-in-half plastic baseball. It leaves a seam around the ball, but it's pretty solid.
I'd post a picture, but I don't have a site. Great advice from everyone.