Dear Dr. Fred,
Q. Do I need to have my granite countertops sealed? I have heard so many conflicting answers.
A. There is very simple way to tell if your granite, marble or limestone countertops or floors need to be sealed. Take a drop of water and place it on the stone. Wait about two minutes and blot up the water. If the water left a dark mark, indicating that the stone absorbed the water, it must be sealed.
Do keep in mind however, that sealing a stone is done to give you more time to clean up a spill so staining agents are less likely to be absorbed. Sealing will not protect the surface of calcite based (e.g. marble, limestone, travertine, onyx, and some granite) countertops from damage caused by acidic liquids. So, even though your countertops are sealed, you will still want to take care to use coasters and avoid acid based cleaners.