Hi Fleur
IMO if you can wash the material and pour off the water until it runs clear you should be fine. It's the very fine 'mud' that will hurt your strength and curing.
3 to 1 should make a strong recipe.

I have made a strong tufa pot from plan dirt in my yard. I screened it to less than 1/8 inch into a wheel barrow and kept washing it until the water was almost clear.
It worked just great, and looks good as well. Very tufa like.

Use the granite dust as is. I use marble dust and silica flour which are both super fine. Billie

Try clay.:)

I won't get my first supply of this til Sunday so I don't know how fine it is. I'll try it as is and get back to you. Thanks for your suggestions. We shall see.

It should be OK Fleur, but remember there are very good reason all concrete aggregates including marble dust and fine silicates are washed first.:)

Tufaenough -- What's the reason for the washing? I have no idea how to do it. Can you give me some guidance? I think there's an old gold pan around here somewhere if that would be helpful. Thanks.

Hi Fleur
I've never studied the science so this is JMO, but it's my understanding that some materials are just too fine for Portland cement to bond. I'm not sure about granite dust however.
I recommend just dumping the material in a big pan or a wheelbarrow and stick a garden hose in it.
Swish the material around with the hose until the water running over the top is reasonably clear. You don't have to lose any fine material other than the stuff that clouds the water.
IMO this should help give you a good clean aggregate and improve strength.

That said, if I was in your position and not in a hurry I would make a few test bricks, half with washed material and half with the material as is and see how well they cure over a period of 10 days or so.:)
Like Billie says, your granite dust may be perfectly fine as is.:)

Let us know how it turns out.

Superfine materials added to cement fall into the category of "microaggregates"...one of the industry's latest hot developments. Adding flyash, silica fume, silca flour and even glass microspheres have become common practice in the formulation of some of todays "engineered concretes". The theory is basically that the finer the microaggregate, the better it fills in the microvoids, resulting in a denser, stronger mix. That said, all of the testing that I've seen has been based on using it in conjuction with other, larger aggregates, so the use of it alone remains scientifically untested to my knowledge. I can tell you that I have routinely used an array of microaggregates in my so-called "neat" Portland formulas for many years with great success. It produces an incredibly dense material that appears to be impervious to water and even most acids. It does, however, require stringent control of the curing process. Anything less than near perfect conditions and it will develop serious cracks and fractures throughout.

Are you saying that silica flour is unwashed?
Not according to my research.
These micro aggregates aren't exactly floor sweepings which is what Fleur is planning to use.
They are carefully cleaned regardless of size.
I do not understand why Flerr is being discouraged from washing this material but I guess you have your reasons.
ALL proper concrete Aggregates are cleaned prior to use.
Organics, clay, etc are carefully measured.
Washing his floor sweepings will only make the material better for concrete. That is simply a fact.

Just had a thought about the Melamine component in your freebie supply. Several of the pricey "superplasticizers" that are used to reduce the amount of water required in a mix are actually a form of Melamine powder. Have to wonder if it will have any effect on your mixture or if the stuff I pay through the nose for is in a different state. Let us know if it seems to require less water than expected...I'd be curious to hear (and see) the results. Go for it...just keep good notes. Best of luck.

Today I drove past the business that I'll be getting the "waste" from. In a locked area, they had stored bags of garnet sand so I think what I'll be getting is not granite but rather garnet. The gal who's providing it said it was really pink so I lean toward garnet and think she misremembered. With luck I should have a better idea tomorrow.

I'm not sure whether or not they're floor sweepings. I'll try to find that out tomorrow also.

If anyone has suggestions on what ratio I should use, I'd be pleased to try them. Currently I'm thinking 1 cement, 2 garnet sand, 1 white silica sand. Have no idea how to cure it differently other than a month in water after deleafing. How would I know if the mix is strong or will crack or shatter? All suggestions or advice is welcome and greatly appreciated. I'll try to keep good records re amounts of all that goes in the mix.

If all you are using is Portland & two varieties of sand, it should be rock-hard within 24 hours. "Full" cure time is considered 28 days and "actual" cure goes on literally forever...but it sets to about 95% within the first few days. Keep it moist by spraying thoroughly then seal it tightly in a plastic trashbag. If you leave it 3 days it should be more than adequate.

I use garnet sand blasting sand and it makes great concrete and does seem to cure quicker than regular playsand.
Gives a nice pink color to white portland.
It's the melamine content that could give your recipe fits.
It's slippery stuff. I wouldn't even want to guess how it will react in crete.
I'll be very interested in how this stuff cures.
I might sand blast some melamine myself to see what it does to a recipe.

Granite, garnet, Fleur, I hope your new recipe addition is a resounding success.

At the same time, my hopes were up for the granite, cause there's a marble/granite countertop fab just down the road. Haven't stopped by - my budget is much too small for that kind of stuff - but now I wonder if their shop sweepings would be an interesting addition. Or if their stone saws have those vacuum bags that pick up the dust....Wow, there really is a whole world of possibilities out there.

To make the best use of this stuff, I now really need to find a source for white portland. None available in my back of beyond town nor in the two larger towns nearby (60 & 75 miles away). I may have to special order it. What a pain THAT would be. Wasted time for the trip to get it and extra $$'s for gas. Poor me...sniff, sniff.

You might try "back tracking" a local vendor by directly contacting one of the major manufacturers of white Portland like Lafarge or TXI (Google'em)and asking where their closest outlet is. I've had to do this on a number of exotic items and it oughta' work for this too.

Well I found the white portland and picked up a bag of the GARNET dust. It is as fine as cement and now I wonder if I should use 1 portland to 3 garnet dust or perhaps use only 2 garnet dust and one of white silica, just to be sure the cement has something to stick to. I'd like to be sure the crete will be strong. I'll also add fortifier as 1/4 of the liquid. Does anyone have recommendations? Thanks.

Hi Fleur
You are on your own here.:)
I use the garnet before it is reduced to powder and it makes great concrete.
I would make a sample brick with added sand and one without.
I'm thinking the melamine powder might give you fits depending on it concentration.
You could find your garnet dust makes horrible concrete on it's own, but works as a terrific superplastisizer additive in other recipes. Get making those bricks. I'm very excited to hear your results. You are doing my most favorite thing, going where no Tufateer has gone before.:)

Beam me up Scotty!

Just a FYI . You can puchase crushed granite at farm supply stores . Sold as chicken grit.

Cool.
I've seen the bags when I buy my vermiculite.
I thought they were an organic product.
I'm going to buy some chicken grit tomorrow.

Chicken grit and gravel is also good used as a mulch in pots or beds. Water flows through, doesn't absorb water and keeps ground cool and moist.

As far as what ratio to work with...run some "control" tests and let the materials tell you what works best. I often play mad scientist, dumping all kinds of stuff together and mixing it up...but I always try to impose a little "method" into my madness. Keep some measuring spoons, cups & such handy in your workspace and try several mixes using different proportions of whatever "new stuff" you are experimenting with. You can do this in very small volumes and still get very precise results by working in "parts". They are infinitely scaleable and whether measured in grams or in truckloads, can be easily converted up or down to fit any application.

Once you have a method for mixing, you need something to put the mixes in. Keep an eye out at yard sales for non-stick baking pans. I find muffin pans especially handy. I can put small measured quantities of a dozen different formulations in a single pan for comparison ( Use a little release, as I have had some mixtures even stick to "Non-Stick" ). They are especially useful for color tests and also easy to enclose in a curing bag. Permanently scribe each form with a number or letter (it's hard to write on Teflon), then just note what mix went in each and compare the results.

Consistent measurement is the key when working with very small quantities. If you can find a gram scale or Postal scale it will help insure accuracy, but plain old measuring spoons will get you very close as long as you "load" them all the same. Best bet is to pack them and scrape them level.

Hope you find some of this helpful and best of luck.

A 1/2 inch thick sheet of blue styrofoam is excellent for making samples.
You can cut many identical holes in the sheet.
I have several.
I drill 3" 2" 1.5" 1" round holes and cut a bunch of 2"x 8" and 1"x6" holes in sheets 2 feet by 1 foot.
These 1/2 inch thick pancakes and bars are very uniform because you can really force the mud into them, and they can be cured right in the mold just covering it with plastic. You can even stack the sheets in a corner for a month.
I use my samples in my projects. The various size round and colorful disks look cool pressed into the sides of a pot.

hi Guys from Australia,

As a building tech.. some info about cement. A large part of the ability of materials to harden is about their particle size. This is why cement manufacture produces 5% of the CO2 emissions on the planet - the ingredients are cheap but must be ground down to a powder in huge rotating inclined pipes full of metal balls - a ball mill.

A concrete "batching manager" is a master of the art of mixing materials of different grain sizes. This effects cost.. also strength.. also shrinkage.. also wet "workability" (measured in a std. "slump cone") of the concrete.

Garnet is super hard, and even when a very fine powder the grains have sharp edges from it's habit of fracture - which also makes it ideal as an abrasive -, so it will bind well in the mixture. It's hardness will increase the strength of the concrete dramatically provided the correct proportion of cement is maintained (since that is the matrix). And so all things considered, it is the proportions (ratios) of the mix that are very important, for different combinations of grain size create different bonds due to the way that the materials fit together. Also, only enough water should be added to satisfy the need to cause a reaction in the cement. Never add too much water.

You would need to be a very skilled batching manager to predict the perfect proportions of this garnet sand sweepings material for a desired goal. Therefore, experimentation using different proportions is the best possible way. The presence of melamine may effect the set and cure time, but super plasticizers do not effect ultimate strength.

But I note this from experience over these 45 years: when you use a lot of fine material in cement to produce a hard cement it tends to shrink rapidly during the cure. The rapid shrinking can spit your work into many pieces.. especially if it has no reinforcement ( mesh) to distribute stress around the workpiece. This is like a lot of super-hard materials - they are also brittle. And so there are 2 ways to overcome this (1) use a highly controlled cure by isolating the finished piece in a humidity controlled environment ( often achieved by wrapping in plastic ) along with cooling during the initial chemical bonding period with water quenching when the heat of hydration can be excessive (2)or Increase the amount of coarse aggregate in the mix. Introducing more coarse aggregate will produce a weaker cement, but if a hard material such as granite chips are added it will still be of high strength.

Of note: The Romans used many "secret" materials to make the render coat on the inside of their aquaducts.. most of which renders haven't eroded after 2000 years of water flowing through them. Upon testing these render coats have been found to be over 900Mpa yield - the hardness of glass. So it pays to experiment eh.. mind you analysis has shown a small percentage of urine in their mix so perhaps they were just lucky and drank a lot of vino while working, then pissed in the wet cement..

This post was edited by Chilby on Thu, Jul 17, 14 at 4:53

Hi Chilby,

I was wondering if I could email you directly for some advice/recommendations and instructions on this topic? I am a student in AUS and have a design project coming up that I wish to work with Garnet and concrete for.