There are several benefits to choosing a stone window cill, chief among them is the durability of the material and that it is low-maintenance. Unlike wood, which frequently needs repainting and other preventative maintenance for rot, termites, or paint fading, stone window cills resist damage from sun and moisture exposure. While they are very durable, stone products do require some maintenance.
Most often for simple cleaning and upkeep you may use a cleaning product purchased at a retailer or compose a basic mild cleaner at home. If you make a cleansing solution at home use a spray bottle with a weak solution of washing up soap and water. To clean the surface of the window cill, spray with either the purchased or home-made cleanser. Afterwards, gently buff with a clean, soft rag. In either case, use a sponge or cloth to clean your window cill, never steel wool or other abrasive materials.
One other maintenance item is to protect window cillsfrom mould and mildew, especially for windows that are heavily shaded. Weather permitting, keep windows open to provide air flow and reduce the build-up of moisture on window cills. In winter months, a closed storm shutter can reduce the amount of rain and snow that accumulates on the cill.
It is a good idea to regularly check the integrity of the sealant used on your window cills. In most situations an annual check of the sealant is sufficient. A simple way to test the seal is to place a few drop of water on the cill. If the water beads up and stays in place then the sealant is intact. If instead the water appears to be soaking into the stone it is time to reseal. There are several sealants on the market made from various polymers that can be purchased from your local a DIY (Do-It-Yourself) hardware store. Otherwise a professional stone mason or contractor can provide services to reseal the window cills in your home.