Yes you can use a hypertufa mix to sculpt with, or you can carve it. For sculpting make your mix thick enough so that when you squeeze it it stays together. You can enhance the mix with a little bonding agent, however my experience with adding fortifier or bonding agent to a hypertufa is that it will make it less carvable later.
Peace is made with a vermiculite mix, Happiness has perlite.
Both are done over a chicken wire armature, and once the first layer of hypertufa was added to the armature (patty method), then a sculpting layer was added on, misting the first layer with water and brushing it with bonding agent to insure the sculpting layer will stick. The sculpting layer could be pushed and pulled and textured if needed. If I was concerned that there was not a good bond, I would use a paint brush and gently but firmly press water/bonding agent into the crevices that need attaching more securly.(Peace is pictured first using the arrow key to the right you can then see Happiness)
Happy casting, and sculpting,
Dena

Here is a link that might be useful: Peace and Happiness

Those are both quite lovely! Hopefully my endeavor turns out half as good. Can you get the cement in lighter colors?

What kind of bonding agent would you suggest? Is it harder to carve later because it is harder?

Even more Thanks.

A very good recipe for this is one that uses cryogenic perlite in place of some of the sand.
Cryogenic perlite is like weighless white sugar and makes a cement mud that is soft and workable like mashed potatoes (It feels exactly like mashed potatoes as you mix it) and easy to carve for several days.

You can do concrete in almost every color except purple using pigments. I do snow white to pitch black. Here are just a few. It's an old picture. I do many others including a green/blue that is very pretty under a gloss sealer.
Except for the blue they are very inexpensive and are designed to handle many many years in direct sun without fading.
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Where does one get those colors? Additionally, do you have any pictures of 'tufa made with the cryogenic perlite you talked about earlier, and where do you get that from?

Thank-you for your wonderful pics Dena and David,
I am making a birdbath for my mom with leaves on the column. If I paint them with ardrylic paint what should I do to the hpertufa first?
Debbie
I'm trying to post a pic through photo bucket.Hope it works.

Regarding color of concrete. Both Peace and Happiness were done with varying degrees of dry charcoal colorant. Each weathered the summer heat and turned lighter as they became drier. They are outside in the pouring rain and are quite dark right now. I did not seal either one as I want some natural patina, i.e. moss to attach.
As David has mentioned there are several grades and sizes of perlite, and also vermiculite. If you buy several bags each one will vary slightly, good to have a lidded bucket to gently pour the ingredients into then mix to the bottom before each use and scoop, to get a more uniform mix.
Debbie,
My experience with acrylic paints and tufa/concrete is that you have to do no preparation other than knowing it is clean. I have painted things as early as a week after it was made.
I mostly use watered down acrylics and may use several layers of color. You do not have to seal your work, however the colors will stay truer for longer if you do. There are products designed specifically for concrete sealing, from satin to high gloss. Lowes and home depot carry many. If you allow the sealer to penetrate and cure as the directions state it should not be harmful to animals who may take a liking to the water inside the bowl.
Happy casting, look forward to pictures.
Dena

The colors are all from dry pigments designed for adding to concrete.
They are natural pigments that do not fade.
Some colors (especially blue green)can be hard to find but check with a supplier that provides concrete products for commercial builders.

This is the only picture I have of perlite carving/molding.
It was my first done months ago. For various reasons I no longer post pictures of my work.
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Thank-you!! I can't wait to finish my projects.
Happy casting to you too!
Debbie

Dena:
Earlier you mentioned using a bonding agent, what bonding agents would you recommend?

GF,
I use the bonding agent that is located in the cement products isle at Home Depot or Lowes. I use bonding agent instead of admix/fortifier for most things where I use an additive. Bonding agent is similar in appearance to Elmers glue, and thickness. I add a small amount into the water that is my first water into the dry mix. The amount I use per mix is sort of eyed, in general 10 cups of dry mix (approx 3 of the cups being cement)will have about 1/4cup of bonding agent in it
There are as many bonders and fortifiers as there are perlite, vermiculite and other additives that can go into a mix. You can even use Elmers glue, but I have not tried this, I am sure there are others who have.
You can mix the bonder with plain cement for a bonding slurry as well.
Hope that helps
Happy casting,
Dena

Whoa, goodness. I feel like I should be getting some books on how concrete is made or something. We would like our sculpture to look like the native coquina here in FL, so white portland is probably a must (if anybody knows where to get some in Southern BrevCoFL, let me know!). I was planning on adding just a hint of a buff color and using crushed shells instead of gravel, with an outer layer that also had spanish moss and seaweed in it so that it will look rather rustic. Our goal is to make something that will look as if it has been there for ages within a few weeks or days of placement and will hopefully last for quite awhile.

Does adding the bonding agents affect the finish? Does anybody have pictures or can describe it well enough so that I will know whether or not it will work for our project? Sorry if I am asking too many silly questions, feel free to refer me to other threads if my questions have aleady been answered.

Everything in my pictures above contain bonding/admix agents in various amounts and combinations.. Once you take a wire brush to surface it's not going to make any difference in appearance.:)
Shells replacing gravel will result in a weaker project. I suggest a good amount of admix and generous portions of Portland to compensate.

GF,
I had to look up coquina and the images I see are sort of a conglomerate of shells and sand and putty or buff 'lava' stone. The use of white cement (which I think is more in abundance where you are, builder preference)perlite and some vermiculite along with either a brown mason sand or regular old play sand will yield a very nice coquina look. The surface of the coquina looks very rough and gouged so I would make my mix a little drier and sort of pat it on and pull some off, placing shells where I want them, but could use finer shells in the mix. Your shells should be washed and dried before adding them to your mix. If they are a commercial package bag of shells it is likel;y they have been washed several times. Salt will affect your mix, but may be just what you want with this rustic venture.
I hold on adding more bonder or admix, and maintain portions for a good solid mix. Adding additional portland to a mix can weaken the integrety/strength. So many opinions. I am one to experiment and would try a small coquina batch and make adjustments from there.
Happy casting,
Dena

I agree that experimentation seems in order...I think we'll get together and practice with many small batches, maybe end up with some extra decorative stuff to go along with the statue or something.

I'm assuming that salt affects the mix by preventing a proper cure, or something along those lines?

Salt is bad, but shells have other problems as well. Cement doesn't adher to them nearly as well as stone. In fact you can take two identical oyster shells and fill them with portland cement and one might stick like crazy and the other will pop right off. I've overcome this using a strong recipe with admix.

Thanks to all of you for all your help and recommendations.I've done some Hypertufa work mostly stepping stones. Thanks again. I find that old cake pans and older Tuperware work great as molds. Then I just use Vaseline as a release agent.suprised myself how well I did!