Artificial Rock Final Preparation
Your artificial rock will transform right before your eyes
Now that you have let your artificial rock cure for a minimum of three days you can begin the process of changing the artificial rock from being easily identified as concrete to being indistinguishable from real stone. The sculpted concrete has a rough feel and texture to it which you will be removing with a grinding stone. The end result that you will be looking for is to have the artificial rock feel smooth to the touch.
You are not trying to scrape away all the fine textures you have sculpted and imprinted into the artificial rock. You are only trying to remove the outer layer of cement.
A respirator is an absolute MUST for scraping your artificial rock
You can not breathe the concrete dust as you scrape your rock down. Many people use paper filter masks or nothing at all. Truthfully you must have a respirator with cartridge filters as the minimum to protect your health and safety. Open space with good ventilation is strongly recommended.
If your project has been built directly in its final position and you will not be moving or transporting it you can skip this step. If you plan to move the rock at all in the future you will want to flip it over (very carefully) and remove as much of the breakable points along the bottom edge as possible. Since when you lift the rock you are probably going to stand it up on its edge, this can cause breaking in along the edge. This is not a problem now as you can simply grind it to a smooth edge again. But in the future once you have painted your rock you will not want any more of the edge to chip or break as this will stand out like a sore thumb in the finished product.
If you are going to flip your rock upside down you should wait a minimum of two weeks as the concrete may not be strong enough after three days to withstand being balanced on end and flipped over.
Washing the artificial rock is a very important step
After you have scraped the artificial rock down completely you will find that there is concrete dust in every possible nook and cranny which MUST be removed before you paint or color the rock. As a minimum you will need to use a soft wire or stiff plastic brush to scrub the entire rock down with. Do this while soaking or spraying your rock down with a garden hose to ensure that you get every possible spec of dust off of it. The method that the professionals use for this step is a very weak muriatic acid solution wash, but this is not necessary as elbow grease will produce effective results without having to handle dangerous muriatic acid.
Let the artificial rock dry for a minimum of one full day to ensure it is completely and totally dry before moving on to the painting and coloring stage of artificial rock construction.