Sealing Natural Stone Surfaces
In short, all natural stone surfaces need to be sealed periodically. This is because stone is naturally a porous material and can absorb bacteria, food particles, and liquids that we use throughout our home. Not sealing a stone countertop or floor tiles — which get the heaviest traffic and are the most susceptible to wear and tear — leaves the surface vulnerable to absorbing foreign substances, which can weaken the stone and potentially lead to the growth of bacteria.
That being said, not all stones are created equal. Marble, onyx, and limestone are some of the most desirable stones on the market, but all three are very susceptible to staining, scratches and, in particular, to acid etching. This means that if an acidic material touches the surface of the stone, it will leave a dull mark that may be difficult to remove. Because these stones have a high porosity, it’s important to seal them about every six months and clean them with solutions specially designed for natural stone. This upkeep is essential to making sure your floors and countertops remain beautiful and functional for decades to come.
In contrast, granite and quartz are much less porous and don’t need to be sealed as frequently — about once per year will be enough to seal up any exposed pits and fissures that can harbor bacteria. In addition, granite and quartz don’t require special cleaners, just some soap and water on a soft cloth is all you need to mop up any messes that occur.
The good news is that sealing your stone surface won’t cost a fortune. You can expect to pay between $40-$60 on a conatiner of sealant, depending on the formula and manufacturer. You can also seal the stone yourself in just a few easy steps. While it’s important to follow the instructions that come with the sealer you buy, in general you’ll want to start by thoroughly cleaning and drying the countertop.
Stains from Food and Grease
When natural stone is left unsealed, it can quickly absorb food and liquids and lead to deep stains in the stone. This staining can happen in a matter of minutes, even if you’re quick to wipe up the spill. It’s not just liquids you have to worry about. Natural stone can also absorb grease and pigments. Leave a carton of strawberries on unsealed stone and you may discover a deep red square on your otherwise flawless countertop.
Damage from Cleaning Products
There are many common household cleaning products that can damage natural stone, even if it is sealed, but unsealed stone is even more susceptible to this type of damage. Some cleaning products contain citrus, which can quickly eat away at the calcium in the stone and leave pits. Chemicals that seep into the stone can damage the finish and cause discoloration. A sealer works to seal the cracks and tiny fissures in the stone to keep stains from going deep into the countertop.
Stains from Water
When granite and other types of natural stone are properly sealed, they repel liquids and prevent them from permeating into the stone. Unsealed stone absorbs liquid quickly, which can become a problem in a kitchen or bathroom where countertops are bound to get wet. You might think something as natural as water wouldn’t be a problem, but it is. Without sealing, water will penetrate the stone and leave behind water marks, some small, some large, giving your stone a perpetually dirty appearance.
First: Test to See If Natural Stones Need Resealing
Just because your natural stone counters are properly sealed at first does not mean they will not eventually absorb liquids and develop stains. Frequent cleaning with products specifically made for natural stone is essential, and you should also wipe up liquid spills as soon as you can. When you regularly use a stone-safe sealant or your counters, you have time to clean up spills because the liquid is forced to bead on the surface. If you let the liquid sit, it will start breaking down the seal.
To test the seal of your stone counters, all you need to do is pour some water on the surface in various spots. First, sprinkle a tablespoon of water on your stone. Leave the water on the surface for about 15 minutes. If the stone darkens or if the water is absorbed in less than 4 minutes, then resealing is needed. By testing the stone for "thirstiness", the tester learns whether the stone needs to be resealed. This experiment can be done every few months to inspect the quality of your stone. Make sure the water spot has evaporated before sealing.
If the water is still puddled after 30 minutes, or if it evaporates without staining, the seal is in good condition and you do not need to seal your stone. However, it’s still fine to go ahead and seal the stone if you wish, as it’s not possible to over-seal stone. When a stain appears in less than 30 minutes, you need to apply a new seal.
How to Seal Natural Stone
1. Deep clean the stone.
Cleaning your surface before applying the sealant will ensure a more even application. Make sure to address any unwanted stains, because once sealed, the stains will lock in - which, of course, is something you want to avoid. Use a pH neutral cleaner and a lint-free cloth to wipe down the surface. Then, make sure the stone is completely dry before moving on to the next step.
2. Wear gloves and ventilate the area.
Most sealants are harmless but always take safety precautions. Wear gloves to protect yourself from harmful chemicals. Also, to avoid potent smells, open a window or turn on a fan to ventilate the area in which you’re working.
3. Test the product on a small area.
Always test your product before tackling the whole project. This is to ensure the sealer is compatible with the stone. If the sealer leaves a hazy residue or causes discoloration, use a different product.
4. Apply sealer with a soft cloth.
Always follow the manufacturer's application instructions. Manufacturers may require specific techniques or amounts of sealer depending on if the stone is polished, honed or flamed. Protect any surfaces where you don’t want sealer (i.e. faucets, sinks, stovetops, or walls). You can use plastic wrap for appliances; a magazine cover in between the wall and the stone will suffice. Follow the manufacturer’s instructions for “curing” time, as it can vary by product.
5. Remove the sealer.
The stone will absorb some of the sealant, however, there is usually a bit of excess left on the surface. Use a microfiber cloth and soak up the excess. You don’t want leftover sealer dried onto the counter as this can cause discoloration.
6. Apply additional coats (as needed).
Applying additional coats are normal. It is usually recommended to get the best coverage. We believe it never hurts to be thorough! The more porous the stone, the more likely additional sealer will be used. A general rule of thumb is to wait 15-30 minutes in between coats.
