Yep, Tango,the 'Savvy Old Masons' were right on the money with their observations about sand not always being what it's supposed to be. Just this week, I finished a job, a feature stone wall done in faux stone, ( made in America, actually,) and I went to the extra trouble, dollars, and miles, to buy 'Washed Sand' in 30litre bags for the job, as it was a display in a design show with a real tight schedule, and I wanted every thing to be right.
I wasn't allowed to use any additives or modifiers, just plain old sand, cement and water. They bulldoze it down a few days after the show.
Only did a few square meters (yards) of the wall, and noticed efflorescence starting to appear 0n the stone face.
The guy working on the wall next to the one I was laying had none. He bought his sand bulk at a yard. Didn't know if it was washed or not.
We used each others sand, to see what the result would be. Everyone uses a slightly different mix to suit his way of laying, like water content, etc, so we still mixed our own mud, just used each other's sand.
He ended up with the salt bloom, and I had clean stone.
So it appears that the 'washed sand' was the culprit.
Had to resort to using other methods to remove the efflorescence after laying.
Next time I'll try the solution test, and see what that reveals. I've done it with brickie's sand, because of the high clay content, but only recently started using bagged 'washed sand' instead of bulk, and believe it or not, never had any problems with efflorescence.
Looks like I should've stuck with the half ton of bulk sand in the back of the ute. (Pickup?)
This job prompted me to consider using an efflorescence additive called Efflorein, on the jobs where I can use additives. To see this product, and many other interesting concrete/mortar products, just Google the product name.
I've used some of their other products, and find them to be excellent, for example, oxides, and superpolymers.
So it seems oils ain't oils, and sand ain't sand.
Just a bit of information for those interested,
Slate

Sand is interesting stuff.
This spring HD had bags of playsand that were sharp, course and made great concrete.
Playsand from Target was fine, rounded, and dusty.
Now the Home Depot sand is poor quality as well.
I get efflorescence on bricks that are 100% perlite and white Portland. I suspect it's my water, very hard here. Very delicious for drinking however.
Now I'm considering using bottled water for my Tufa.
It never ends.:)

You are correct again...water ain't necessarily water...at least it's not chemically the same from here to there. In fact my well water has change dramatically over the past two years and I'm now having to battle efflorescence. May look up the Effloren that Slate mentioned...thanks for the tip, mate.

This probably explains why my water bath cured stuff is worse than my bagged and misted stuff.
I'm looking into Effloren as well. Thanks Slate.
Efflorescence removal takes up a lot of my time I would rather spend making new projects.

Sorry guys, I should have been more specific. The company you will look for is Ability Building Chemicals, in Australia. Keep looking when you get on, as they have a number of individual pages for products they sell. I have also used their oxides for coloring, and they are excellent, I have found. They will send you samples to try, which is handy.
I'm in the process of trialling their superpolymer, Able Strength. I think it will give me the results I'm after with the work I do, & also my 'hobby'.
You all have the benefit of being on the winning end of the exchange rate, too,
Slate

The "Exchange Rate" sounds like a good excuse to book a trip down under. Hmmmmm...maybe I could write it off as a "business trip" if I picked up some concrete chemistry while I was there.

Tango, you said your well water has changed dramatically the past two years, have you had drought conditions too?
Do you get efforescence in your 'neat' cement mixes, or just in the sand/cement work?
I poured a statue a couple of weeks ago, and changed the aggregate I used, (tried ash to reduce weight), and got strange efflorescence-like marks on it. Can't take anything for granted, have to test just about everything on a regular basis.
I only use one brand of cement, cause I know the others aren't up to the mark, but I have noticed variation in the performance of the one I use, from time to time. Although I've found that certain additives tend to hide a multitude of sins.
BTW, the stone wall installation I spoke about, in this thread,was part of a design exhibit at the Sydney in Bloom show this week. I got a call yesterday morning, saying the display took out the grand prize at the show.
Still over the moon about it. So satisfying getting a good result after putting so much research and work into installing it. Not to mention the leads it has generated.
Let us know how you both went with the search into the cement modifiers at Ability Chemicals, you might try something I haven't, that we all could learn from.
Trying a new Limestone Render here soon, that's made from limestone sawing dust/grit from cutting limestone blocks, mixed with French Cement. ( Don't know about the latter yet). But it looks fantastic, and has miles of design possibilities.
I'll post when I've tried it.
Adios,
Slate

If the sand in Slate's project was causing efflorescence, it was probably beach sand. Sometimes even washing will not get the salts completely out. If you have a water softener, this can cause trouble too. I can always tell if the sand I am using is from a beach, especially if I am using a dark colorant. It's not very pretty, especially in bird baths.
Is there any way to test for salts before using your ingrediance?
Jo

I was going to ask that very same question. We have very hard water here and the water softeners use those giant bags of salt to process the hard stuff out.

Are we doomed to wash all of our sand with hard water first?

Slate --- Congratulations mate! You are, however, required by law to post some pix here before it's official. Sounds great.

Like you, I've noticed that I get more noticable efflorescence when the fly ash content is high. Must be a connection. And yes, we did have a significant drought here during the first part of the summer, but now have Hurricane Rita on my doorstep at the moment, which will likely dump a years worth of rain over the next 4-5 days (not the preferred method of "catching up"). Thought about leaving, but this has turned into the largest mass evacuation in history and the roads are literally backed up with stationery traffic for over a hundred miles in every direction. Guess I'll just hunker down and sit this one out. My guess is that it will steer to the East of us and put us on the "soft" side of the storm, but the weather service expects hurricane force winds to penetrate about a hundred-fifty miles inland anyway. Oh well, as they say in France..."Se La Dang"...(well, at least that's what Texans in France say).

Speaking of France...what's the scoop on "French Cement"? Are you referring to the LaFarge brand or some mixture that requires Perrier instead of water? Like to hear more.

Hope my computer and the house it's in are still here in 48 hours so that I can check back in. I really would like to see the winning entry. Once again, congrats.

Sit tight, and good luck, Tango. I'll be checking after the weekend to see an update from you, I'm sure everyone else will too!
Christine

Hi, folks,
can't imagine what you are going thru, with the impending hurricane and all the upheaval that goes with 'preparation' for it's arrival, or just the internal and physical displacement that is evacuation. World weather patterns sure are a mess now.
Yesterday the news told us it was a category 5, today they say downgraded to cat.3.
To me, it's still a hurricane. We hope and pray that it will weaken, and not cause the devastation the last one did.
Jo, yes the sand I'm talking about is beach sand, it's called 'Sydney sand.'
Don't know if this makes sense, but I use it because it's 'accurate'And is strong. It is the standard sand used by tilers for cement beds, or screeds, and for grouting. Some call it plasterer's sand. As I said, never had a problem with it until I used the 'washed' version. The washed version may be from a source with such high salt content, that it HAS to be washed, but still ends up with salt residue that affects the work. Believe it or not, this sand is more sharp, than smooth. I haven't encountered any problems with oxide in it, ( mineral colourants), but I do have to control accurately, the amount of plasticiser in the mix, or it will cause what looks like a cold joint in the finished piece.
As for testing the amount of salts in the material, I was told to use a salt meter they use in hydroponic food and flower production. The method is similar to Tango's sand and water in a jar, only you test the water with the meter, and it will tell you if you have excessive salts in the material.
Tango, I don't know what they mean by French Cement, I'm having a hard time just getting the price out of them. I think they have a new product, and are testing the water as far as information and pricing go.
Looks like they will send me a couple of 40kg bags to trial soon, though.Can't wait to try it.
As for pics, I borrowed a digital and got some shots of the exhibition, and some other stuff , and it's getting put onto disc, and then I will try to post it here . May be of interest to someone out there.

Slate

Hey,Tango.You still out there?MSN rprots that Rita was downgraded to a Cat 1,so we all hope that you(and the other members lucky enough to live where you are)are safe and sound.
Cheers from the Great(Non)White north!

Thanks to all for the concern. We were fortunate in that the hurricane veered to the east and weakened at the last moment, putting most of the greater Houston area on the weak side of the storm. Lots of limbs down here on our old farmstead, but thankfully nothing serious. Biggest problem has been the unprecidented scale of the evacuation. Estimates have run as high as three-million plus people all hitting the road at once with (unfortunately) predictable consequences...chaos and 150 mile long log jams of cars in every direction on the evacuation routes. News sources are saying this was likely the largest and fastest evacuation in history. Glad I sat it out. Having lived in "hurricane country" all my life and even working as a freelance photographer/stormchaser many years ago, I have a deep appreciation not only for the power that Mother Nature can muster, but the way she can still confound our best and most scientific attempts to predict her actions. Maybe I'm just old fashioned, but I think we should go back to naming hurricanes exclusively after women. We clumsy menfolk simply can't compete with their ability to defy predicting.

My thanks & best to all and I sincerely hope everyone else faired as well.

To find out whether there is salt in the sand, so the jar of sand and water thing, and once it has settled, measure the conductivity using a digital multimeter set to ohms. Compare with tap water (make sure the electrodes are the same distance apart each time). Salt makes the water much more conductive. This test only works if your water is fairly pure to begin with - use rain water or distilled water if the tap water is already quite conductive.