OXY

["Kent and Karen Ivey" <kkivey@zzzzzzz>]

Martin

The archives have a pretty thorough discussion of the flame treatments, I myself have no experience at all with  granite except that I tried out my usual techniques on a piece of Texas Pink and found out I need to stay on the porch with the puppies, you guys that work granite are Full Grown  Hard Rock Dogs.
I have seen some tools on the net , and  some pretty good discussion here about a.. Jet Tool ?
Out of my League , Sir !
The mosaic sounds double cool !   You do not say what the size of the molds are , are they flat tiles you are casting?
If I were going to start from scratch on a project like that, I would  take these things into consideration:

1- Climate - will the mosaic be subjected to a severe freeze/thaw cycle? This is the killer of concrete, but there is a wonder  fix for it. Entrained air admix in liquid form when you are mixing the batch builds in a matrix of microscopic bubbles that act as a buffer and pressure relieving spaces for the pressure from any ice that may penetrate the surface of the cast pieces.  My admix supplier is a company called DeGaussa,  but there are many others . W.R. Grace company seems to do a lot more research and promotion of artistic concrete  products. Easiest way to get air is to meet your local redimix operator. Take him to lunch , we concrete guys would move Heaven and Earth for a free lunch !

2- Setting- is this a floor mosaic , will there be heavy traffic on it? If there is any traffic at all , I would add some  pea gravel to the mix. It will still be easy to mix and batch ,  but the stone will add much to the strength.  Just tamp the surface a little , and the cement/sand paste will still come to the top for finishing.

3-Curing- this is one of the most important things. Is the show side down in the mold , or is it the strike off side? Either way , the optimal cure temp is about 70-80* F, in a humid environment. This is easy to do , just use an old blanket soaked in water , cover the molds when they have taken the first set , and keep them warm for about three days. This will greatly prolong the life of, and allow the true strength of the concrete to come through. Here you can also use a Cure/Seal product that will take the place of the wet blanket, just brush or spray on a cure /seal like W.R. Meadows TIAH, this is a crystal clear  coating that will trap the mix water in the concrete  so that the entire amount of water will be available for the hydration process... which makes the concrete as strong as it can be.
Cure/Seal products are  found at places like Lowes or any good masons supply, look for a Quickcrete product also.
After you strip the molds,  you should also seal the  molded surfaces, to complete the cure process in the best manner.

4-Grade-  is the mosaic self draining? if there are "bird baths", places that hold water , it is going to deteriorate, and will overcome any thing you have tried to build in , strength wise. If it stays wet, freeze thaw will get ya , sooner or later. Shooting in the grade with a level/transit/laser  is important. Also , what is below the concrete/stone dust ? course sand or fine peagravel , graded to drain , or slightly crowned, that is what makes it last. Look at how the Romans  built their roads, those guys  did it right, and they did not have the phrase "Planned Obsolesance " in their vocabulary.

5-Soil-   does the soil have a high sulphate content?  Usually Type 1-2 cement is just dandy, but if there are sulphates in the soil, then you should use Type 5 cement. This resists  sulphates , which will eat up the cement. Also , is there a high salt /mineral content in the soil? If so , the salt/minerals may wick through the concrete and cause efflorescence, like saltpeter growing on damp brick walls.
Here again , good drainage is key.

6- Maintenance- when you complete the mosaic, I would again seal the whole thing , using a masonry sealer. You can find these in high gloss, semi matte, and matte, depends how you want it to look. Seal it every few year and it will last  good and long.

Hope this is a bit helpful, I would really like to see your mosaic if you would not mind posting it.
Kent Lee Ivey,
Concrete Guy, No Letters After My Name.
Big Spring Texas