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Hypertufa Kid

 Here is a copy (edited a little) of some emails I recently exchanged with"Alex" (not his real name).

I hope you find them interesting.

 MY name is Alex and I live in Albuquerque 

 I make Garden green men and gargoyles and I am having a heck of a time finding the right concrete recipe to cast them. They are small most no more than 8" tall or across with very fine detail. I have experimented with making my own hydrostone but it sets very very quickly even with adding vinegar to slow the setting time and it really has very poor structural integrity when its sets.

So I have gone back to using concrete but it takes forever to set and is very fragile when it comes out of the mold. I lose many noses and eyebrows out of the pieces when i pull them from the molds.

So I ask for your advice on this.

 Have you tried hydrocal? You mix it like plaster - it expands a little when it sets - but on a 8" casting it should not matter much. When it sets it is very hard (way harder than pl;aster), but imperfections can be sanded out easily.

You can buy it anyplace they sell supplies for contractors in the drywall business. The last sack I bought was a bout $25 for 25 pounds.

It is easy to use and captures detail well.

 Hydro cal is the same as hydrostone with white Portland cement instead of grey. I know it is a mix of plaster and Portland but I cant work out the ratios and slow the set time.

More over it breaks down in the weather thats is why I am looking for a low cost cement mix for small detailed items.

So if you know a good one drop a line

 I can't think of anything that might help you Alex except finishing concrete. You probably tried it and didn't have any luck.

 Last night I remembered a guy I know was making small statues using very fine sand mixed with his Portland cement. I don't know where he was getting the sand, but it was very fine almost like Clay.

I remember he told me that he used to go around to hotels and take sand out of the ashtrays but it wasn't good enough.

The only problem he had was because the sand was so small there was no real strength in the concrete. But like he said for decorations it didn't matter anyway is not like they had to withstand a nuclear blast or anything.

I was wondering what would happen if you use something like talc, or maybe get some clay and dry it. The problem with clay I think would be that it's dirty (organic material in it most of the time) and the resulting concrete would not have much strength.

 I hope this helps some. Del

 Alex says:

 Can you remember the ratio Portland to sand?

 I don't think I asked, I probably assumed he was mixing it like normal concrete Alex.

I would start that way if I was doing it and then work from there. I might be tempted to add some fiber to the mix to compensate for the lack of aggregates. The trouble with that is the fiber may show in the casting.

I guess you would have to play it by ear.

 I was reading our notes again with the idea of using them as the basis for an article.

 I noticed you said the concrete does not harden fast enough. You could try adding a little baking soda to it, this sets it up very fast.

It is a trick from the old wooden boat days when Portland cement was mixed with water to spread over the caulking on the seams between the planking.

The copper bottom paint was painted over this and it had to set fast so the boat could be launched before the paint dried. If the paint was dry at launching it would not work properly.

 Experiment a little - I remember once when the painters put in to much baking soda and the bucket of cement was smoking! It was to hot to touch! It hardened so fast he could not get his mixing bit out of it.

 Let me know if any of this helps, Del