Marble is a porous natural stone that needs sealant to minimize staining. Leaving this type of countertop material sealant-free means any liquids left on the surface will quickly absorb into the stone, discoloring it and dulling the sheen. Dark or acidic liquids, like red wine, coffee, and lemon, are the worst culprits. 

Deciding between marble and granite for kitchen countertops depends on your personal priorities, budget, and style. Both materials have similar costs for material and installation.

Marble offers a luxurious aesthetic and timeless beauty, but it is more expensive and requires more maintenance. It is susceptible to staining and etching from acidic substances like coffee, wine, or tomato sauce if spills are not cleaned up quickly.

Granite is highly durable, heat-resistant, and easier to maintain, making it a practical choice for busy kitchens.

Both materials should be sealed to protect against damage, but they can still be vulnerable to stains if spills are left on the surface for too long.

Standing water can lead to surface discoloration if your granite countertops are improperly sealed. However, it’s possible to remove hard water stains with a baking soda paste. Take more care with acidic liquids, such as fruit juice or red wine, which can leave more permanent stains. That’s why it’s so important to reseal these surfaces regularly.

The frequency for sealing granite countertops depends on several factors, including the type of sealant used, the color of the granite, and how heavily the countertops are used. As a general guideline, resealing is often recommended every 12 to 18 months, but some sources suggest it could be as often as every few months or at least once a year.

The type of sealant is a major factor: water-based sealants may need reapplication every six months to a year, while more durable solvent-based sealants can last for five to 10 years. Additionally, factors like heavy kitchen traffic, frequent use of acidic cleaners, and lighter granite colors may require more frequent sealing to prevent staining.

To determine if your countertops need resealing, you can perform a simple water test. Place a few drops of water or a wet paper towel on an inconspicuous area of the granite. After 10 to 15 minutes, check the spot. If the water has beaded up, the seal is still intact. If the water has been absorbed and darkened the stone, it's time to apply a new coat of sealant. You can choose to seal the granite yourself or hire a professional to ensure it's done correctly.