The frequency of sealing marble countertops depends on various factors such as the type of marble, the level of use, and the specific sealer used. However, as a general guideline:
Newly Installed Marble: If your marble countertops are newly installed, they may require an initial seal to protect against stains and etching. This initial seal is crucial to establish a barrier that helps repel liquids and prevent absorption into the stone. Depending on the type of marble and sealer, this initial seal may need to be reapplied within a few months to a year. This initial sealer can be a color-neutral or color enhancer.  Darker colors may require a color-enhancing sealer to bring out the color. In addition,  there are oil-based sealers vs. water-based sealers.  Oil-based sealers will last longer.
Regular Maintenance: After the initial sealing, marble countertops typically need to be resealed periodically to maintain their protection and appearance. The frequency of resealing can vary but is often recommended every 6 months to 1 year for most marble countertops in kitchens and high-traffic areas.
Heavy Use and Exposure: If your marble countertops experience heavy use, frequent spills, or exposure to acidic substances (e.g., citrus juices, and vinegar), they may require more frequent sealing. In such cases, you may need to monitor the condition of the marble and consider resealing every 3 to 6 months for optimal protection.
Test for Sealing: A simple test to determine if your marble countertops need resealing is the water droplet test. Place a few drops of water on the surface and observe how the water behaves:
If the water beads up and sits on the surface without being absorbed, the seal is intact.
If the water quickly absorbs into the marble and creates a dark spot, it's time to reseal the countertops.