The difference between a porcelain sink that has been sealed and one that hasn't is like the difference between looking through a clear windshield on a sunny day and struggling to see through a windshield that is being battered with high wind and torrential rain. It's just that clear – literally. Basically, sealer prevents dirt, oil, minerals, contaminants and stains from penetrating the porcelain, which means you can merely wipe away dirt and keep the porcelain in a gleaming state. Like other home improvement projects, this is one that will reward your time investment many times over.
Decide between a spray gun or a thick brush to apply the sealer. The former will make the job go faster, but the latter will give you more control over the application.
Spread an old blanket or drop cloth near the sink to protect the area from drips.
Clean the sink with a mild dish soap and water and a soft sponge. Wipe it dry; it should be bone dry before you continue. Ventilate the area by opening a window or turning on a fan. Put on a face mask.
Spray or brush on the sealer as if you were painting the sink. The coat should be thick enough so it sustains a wet, glistening look for about three seconds. Let the sealer sit for about 30 minutes or the time recommended on the instructions.
Apply a second coat in the same manner. Wait another 30 minutes and then buff the sink with a dry cloth to remove any excess sealer.
Test the bonding power of the sealer after at least eight hours. Create a small puddle of water and let it sit in the sink for several hours. Afterward, there should be no change in the color of the sink. If water has broken through the seal, wait several days for the sink to dry thoroughly and apply another two coats of sealer.