If you have slate, you may want to consider sealing it for protection or to give it a nice shiny look. Slate is a foliated rock which will absorb water and other liquids. This can cause staining of the original color and once stained, because the stain will soak into the stone, the slate surface is extremely difficult to clean. Sealing slate will put on a protective covering to prevent staining and keep the original color long lasting.
Choose your application tool. You can use a paint brush, roller, sprayer, or paint pad. Pour some sealer into a paint tray and apply onto the slate. Watch closely for drips as you apply the sealer. Make sure that you apply a thick covering because slate is porous and the sealer will soak in deeply.
Prepare the area that is going to be sealed by removing outlet covers, taping off any wood trim, covering cabinets, etc. Make sure that anything you don't want sealer on is protected. The sealer is usually quite thin and can drip easily.
Once you have the slate clean, wipe completely with a large sponge and water. Then allow to dry completely.
Choose your sealer. There are different types of sealer on the market and the one you use will depend on the end look that you are trying to achieve. Talk to your local tile supply store, they should be able to point you in the right direction and probably even show you samples of different applications.
After you have completed sealing the slate, make sure that the area is kept clean and free of people or debris for at least 24 hours.