BASIC CONCRETE used To make stone veneer is a mixture of:
1. Cement Type 1 or Type 2 Portland Cement
2. Coarse Aggregate (lightweight Preferably)
3. Fine Aggregate (sand)
The aggregate comprises from 60% to 75% of a concrete stone mixture, and cement paste (the combination of cement, water, and possibly pozzolan) makes up the difference. Potable water, which can be provided at 35 degrees Fahrenheit in the summer, or 140 degrees Fahrenheit in the winter.
WATER-CEMENT RATIO: The water to cement ratio of a concrete mix is extremely important to creating a high quality concrete mix. You will want to take GREAT care to ensure that you are using the correct water to cement ratios when making your stone veneer.
Concrete gets hard as a result of the chemical reaction between cement and water which is known as "hydration". In theory, for every 4 lbs of cement, 1 lb of water is needed to fully complete the hydration process. This results in a water-cement ratio of 25 percent.
In the field, crewmen usually consider a mix formed with 25% water as too "dry" which leads to a real-world measurement of 35 to 40% water content. Fortunately, when making stone veneer we can get by using the proper 25% water-cement ratio.
We do have some customers who say they make more money by adding more water. They believe that since they are making a veneer as opposed to a structural element the strength of the stone veneer is not an issue as long as it is within the 1800 - 2000 PSI to meet ASTM C39 code requirements. We do not believe in this method but we do understand the logic. It's ultimately up to the quality of stone veneer you want to create.
Take for example that some stone veneer is going to be installed in the interior of the building, which means the stones will not be affected by outside elements. These stones can be made with more water since strength will not be an issue, as long as you are within building code requirements.
Remember, any water that is not consumed by the hydration process will eventually leave the concrete as it cures, resulting in small pores that will reduce the strength of the concrete. Cured concrete can be as much as 6% air because too much water was added.
And finally, a mix with too much water will experience more shrinkage as the excess water leaves, resulting in internal cracks and external fractures. In short, make sure to keep your eye on your water-cement ratios when making concrete for stone veneer...or any other application for that matter.