Interesting! That brings me back to my lime wash questions. Weak acids (vinegar) are used to isolate casein from milk. The resulting casein is added to lime wash (water saturated with calcium hydroxide) becaues it forms calcium caseinate, which binds much better than calcium carbonate (lime + CO2).

So here's the recipe for "Elmer's" Glue. What ingredient do you think is doing the binding?
#######
1 quart skim milk
3/4 tablespoon baking soda
1 tablespoon white vinegar
10 ounces water

Place milk and vinegar in a double boiler. Cook on low heat and stir as curds form. Drain off liquid. Wash remaining mass with water until the vinegar smell is gone. Put into a clean bowl. Dissolve baking soda in water. Pour over curds and stir until a white paste forms. Seal in suitable containers.
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This tells me that you probably don't want too much glue in the mix or it will weaken it in the long run??? I can't imagine calcium caseinate being better than calcium carbonate for long-term stability. My guess is that's why it's mostly used for adding new concrete to old concrete, rather than as a fortifier. It sounds like the purpose is strictly to get the two to initially stick together, allowing other reactions to stabilize the bond.

I know what it says...I'm hoping someone can tell me why.

Magic?
Concrete is considered to be a 'black Art' by some folks, including the owner of my local batch plant.
I'm still trying to figure out why the phone always rings when I'm on the can.:)

At last! Some of my esoteric fountain-pen knowledge *may* come in handy!

Years back, pen barrels were, for a while, made with casein. AFAIK, nothing else--just casein. And when submerged in water for a long period, they dissolved. (Ink didn't bother them because it was isolated from the casein by rubber sacs.)

A couple of companies nowadays are using casein for some very high-end pens, and yes--they come with instructions to keep them away from water. Go figure.

I, too, am baffled as to why water-soluble substances can strengthen 'tufa, or concrete, for that matter. Doesn't make sense intuitively, and I don't know the chemistry.

Anna

Ha! Black magic, indeed. I wonder if milk protein has become the standard simply because it was readily available back in the old days, or if there's something special about casein? I guess we'll never know. I think if you look hard enough you can find that just about everything has some particular use as an admix for concrete :) Anna, that's an interesting tidbit. I'm stumped!

TE, good luck with the search for the indestructible mix!

With silica fume added it's pretty tough stuff but not white.:)
These concrete recipes meet my needs.
Strong lightweight tufa that resists freeze and thaw is a far tougher challenge.
Concrete experts are so unfamilar with the properties of tufa made with peat that they give you completely conflicting advice on making it strong.
I just have no desire to make stuff that has to be put away for winter to last more than a few years.
Indestructable tufa that floats! That's the Holy Grail.:)

Amen to that! That's why all of my tufa projects up to this point are for indoor use. Although, I think the thieves would get it before the weather would. A neighborhood friend actually saw someone pull up to someone's house, dig up their plants, load them in the truck, and take off :(
I guess I should be looking for admixes to prevent that...broken glass is pretty :)

David, that is a fantastic lantern window! Great job! How did you do the window cutouts? Love the texture!

Marly

Thanks Marly.
I decided if I'm going to use a big candle I want a fireproof window.:)
I just glued little styrofoam blocks to a styrofoam sheet and put a frame around them and filled it with the concrete
Then just ripped it off.
But my new mold will use wood pegs in the styrofoam for the windows so it's reusable.
I already have a mold made using 3/4 inch dowels for round little windows. It should look pretty cool.

The texture comes from course silica filter sand sold for swimming pool filters and stuff like that. Only a couple bucks more than play sand and it has a nicer color in my view.

Is the aggregate in the mix or just on the outside parts? I tried larger(pea size) stones in a mix and didn't see much of the stones. Really like the look Tufaenough.
Paws

Hi Paws
The aggregate is in the mix. It's the only sand in the mix.

I'm just finishing up a tufa pot with pea sized exposed aggregate, but only in the feet. I like the look.
I cast on the outside of forms so it easy to expose the aggregate with a wire brush while the mix is still very soft.
To this point in my tufa hobby I've avoided strong chemicals like acids and stuck to vinegar and good ole fashioned elbow grease but if your mix has hardened up you might need to try it to get those rocks to show.
There are surface retarders, used on sidewalks and such but I've never used them.

Its on my list of "to gets".
Thanks
Paws

Paws if you are casting inside a mold, after oiling it up you might try sprinkling powdered sugar on the mold.
Just like flower dusting a cake pan.:)
The sugar might retard your surface enough that after unmolding a good brushing might give you the look you want.
I haven't tried it but will first chance I get.

Don't know if this helps or is relevent but here goes.

Years ago I spoke with a man who did stamped concrete. I loved the look he created with contrasting areas of smooth and "bumpy." He said to attain that, he painted molasses on the areas he wanted to be bumpy. After 2-3 hours (I think) he washed the molasses off, exposing the bumpy surface. It was something I always meant to experiment with and never got around to it.

Does this sound right to you experienced cement/tufa artists?

Dian it even sounds right to this inexperienced cement/tufa crafter.
I can hardly wait to try that. It makes perfect sense.
Thanks for the great tip.
Now I a three uses for molasses. Bread, beans, and TufaCrete!

You can use molasses as a sticking agent when applying spray mixes to plants. 4 uses now!

Tufaenough

what recipe are you using, and how much elmers glue are you using?

For the little window the Elmers and water were about 50/50.
The recipe was about 2.5 very course sand to one Portlands and white pigment.
Future stuff like this will probably contain at least one part fine sand to help avoid voids.
I use Elmers contractors glue and Acrylic admix interchangably. They both provide me with stronger tufa earlier than recipes without either.

But then I made two small bricks, using acrylic admix in one, and some very old previously frozen latex paint in the other, and if anything the brick made with the old paint is harder and has a nicer finish than the one made with acrylic admix.
Concrete is a very strange critter. :)
There seems to be no end of stuff you can add to it.
I read on the net that a faux bois artist used cornflour in some of his work. Now that makes no sense to me.

I cannot see a photo. :-(

I have dabbled with concrete recently and made stone-concrete steps in the past. But, I am just beginning to expiriment with thin set, small projects. I'm trying to make windows and other small projects. I don't know what to buy for thin set materials. Will adding glue allow this thin set without cracking? Forgive the lack of understanding of chemical discussions.

I wish I could see your lantern window.

The glue or ad mix ( bonding agent) adds strength. IMHO If your projects properly cure ( stay continuously damp) for a week or two, I believe they are less likely to cracking. Also always make your projects when it is about 50o f or above. I have experienced cracking, when I made projects at lower temps. Portland cement 1pt and sand 2pts and some ad mix can be used to create a thin layer - possibly for the windows ( depending how small). You can also buy a product called vinyl concrete patch. All you add is water. It is designed for to create thin layers of cement.

I recently tried a product call shapecrete . It can be purchased on line through Home Depot, or directly from manufacturer. It is thin set mix that is workable like clay - I made this Bowl . This product is a little more expensive, but if you are making small projects it may be worth a try.

Mike

Anyone have recipes with "Silica Fume" in the mix? I have some that i purchased a couple years ago, or more, and wondered if anyone had recipes stating how much silica fume to add in addition to the peat moss, pearlite, vermiculite, and cement. This is what I've seen to be the basic recipe for Hypertufa. My hypertufa efforts have been a couple laughable carved statues, one cats head and I forget the other one, but, I do have the silica Fume, so, any recipes, if I choose to make something worthwhile?

Me and the guys are doing a contest of who can make the concrete beam that will hold the most weight and I want to use glue since it is derived from hide which is an old bonding material so if anyone can tell me the poundage that this concrete can hold that'd be great

Glue is made from hide? Okay, so that's what they mean by taking an old horse to the glue factory? Gross and really sad. I thought they used the bones, I wish I didn't know this.