Sealing is done during the installation and afterwards once per year or according to your installers recommendation. The importance of sealing your granite countertop is to fill in the fissures and make the granite non-porous thus nothing can penetrate. Not all sealant are suitable for granite, the best sealant should be stone cleaner or a stone wax to fill in the fissures. When you seal your countertop then you will reduce buildup of oil particles on the surface. The food substances that are likely to make the granite stain are, tomato, coffee, acidic substances and alkaline substances. The porosity level of granite differ where you will find that one granite slab is more porous than the other.
There is a simple test you can conduct from time to time to determine whether you should seal your granite. Place a water-soaked towel on the granite countertop and wait for 5-10 minutes. Remove the paper towel and if you see the area that was under the towel has turned darker, then your granite needs to be resealed as soon as possible. You need to choose a quality sealant simply because you have spent a lot of money to purchase your granite countertop. Before you begin sealing make sure the countertop is clean, use a granite cleaner and a piece of clothing to wipe any dust and debris on the granite surface. Allow the surface to completely dry before you can apply the sealant.
The process of applying the sealant is very simple, start by pouring some sealant on a cotton rag and rub it on the granite in a circular uniform motion. You need to be certain you have covered the entire surface then let the granite absorb the sealer for about 20-30 minutes. It's important to read the direction written on the granite since different sealants have different wait period. After the first sealer application has dried take another cotton rug and re apply a little more sealer. Do not be in a rush, take your time and work uniformly from one end to the other. Depending on the size of your countertop the procedure should take 30-45 minutes. Once you have made sure the sealant is dry wipe the surface to remove the remaining sealant and then carry out the wet paper towel test to see if you have sealed it properly. If you do not see any dark spot or discoloration then you have successfully sealed your granite countertop.