High quality marble and stone, expertly selected and cut, adds opulence and sophistication to nearly any space. As with any high quality material, maintaining your marble’s original look and feel is a concern as marble is porous, and susceptible to staining and etching. One common solution to protecting and preserving marble’s integrity is the use sealers.
Some suppliers will recommend a stone sealer as the ultimate form of protection without providing much information about it. Sealers can provide excellent protection, but if chosen poorly, applied at the wrong time, not compatible with setting materials, they can result in the misaligned expectations, need for multiple re-applications and other unforeseen maintenance costs.
Considering the cost of fine marble and stone and the value it adds to properties, having a good understanding of its care is critical.
Here’s everything you need to know about sealers, and more importantly, some common misconceptions.
What is a sealer?
A sealer is a water or solvent based liquid that is applied to stone (often marble) and that gets absorbed below the surface. The key product in a sealer is a type of resin. Once the water or solvent evaporates, the resin is left behind; filling in the gaps between the stone’s natural pores, and thus providing some protection against stains from cooking, cosmetic products, and so on.
Most sealers will penetrate the surface of the material, whereas coating-type sealers will, as the name suggests, bond to the surface and provide a type of coating. Often, coating-sealers will change the appearance of the stone and will provide shine. Coating has a very specific application, and is not normally recommended for interior stone such as marble.
Five aspects of sealer that are important to understand:
1) Stain resistance
Sealers help prevent stains, but no sealer can make a stone’s surface “stain proof”. Instead, sealers delay the time it takes for a stain to settle into the stone’s pores. In short, they give you more time to react and to clean the stain. The time you have to take action against a stain will depend on the type of stone, the stain-causing substance (for example, red wine), and the quality of the sealer. It’s why it’s so important to carefully choose a stone and sealer that is appropriate for its application. Certain types of stone will be more resistant to common kitchen stains, and certain sealers will work better against these cooking stains as well.
2) Water based vs solvent based
In order to be effective, sealers must penetrate the stone deeply when applied. Because solvent molecules are smaller than water molecules, solvent-based sealers tend to penetrate more deeply and more quickly than water-based ones. Under the right conditions, however, both water and solvent-based sealers provide excellent protection. Some people prefer the water-based kind, due to the absence of the harsh chemical.
Both water and solvent-based sealers can be used for interior and exterior stone. What’s important is that the resin left behind (once the liquid has evaporated) sits close to the surface of the stone in order to provide maximum protection (delay) against stains.
The amount of moisture in the air varies, and all stone must be able to allow for moisture-vapor transmission—to breathe, in other words. A sealer that blocks this natural transmission can cause deterioration over time as well as discoloration. The right sealer will repel liquids, but still allow air to pass through the stone.
4) Heat and cold resistance
Many materials are susceptible to expanding and contracting due to freezing and thawing, and marble (and other stone) is no exception. For exterior stone, it is especially important to choose a sealer that is capable of expanding and contracting in freeze/thaw conditions. Most sealers and coatings are designed for interior applications, so ensure that you choose the right temperature-resistant sealer for your outdoor stone.
5) Sunlight (UV) resistance
Spills and other accidents can damage stone, but so can sunlight. The ultraviolet from sunshine can cause certain marble and other stone material to yellow and deteriorate over time due to UV exposure. Talk to your stone supplier about what time of sealer to use, especially for outdoor stone, or stone that you know will be exposed to lots of sunlight.
Three common misconceptions to note:
First, sealers do not provide protection from etching as they do from staining. Stains happen when the porous stone absorbs liquid below its surface. Sealers will, in a sense, “buy time”, and allow you to clean the spill before it absorbs. Once absorbed, however, most stains can still be lifted using the right products. Etching is sometimes confused with staining, but it is in fact a form of burn or damage to the stone’s surface, and is often caused by acid. No sealer can protect against this kind of damage.
Second, pre-sealing stone at the factory is often perceived as adding a rain jacket or bullet proof vest to the stone so that you no longer have to worry about staining. That is false. Most sealers are not resistant to installation chemicals and thus post-installation, most of the “resistance” is gone. As such, it is critical to apply sealer after the installation of the marble for greater effectiveness. It’s recommended to then use natural stone cleaners, and to reapply sealer every 6-9 months for maximum protection.
A third common misconception is that sealing stone on all sides is equivalent to shrink wrapping stone and preventing staining or absorption from all sides. This is not the case and not recommended. Not only does this prevent breathability (see point 4) which can internally damage the stone over time, but often the sealer on the back and sides of the stone will void warranty from the setting material manufacturer.
A note about surface tension:
People will often equate the water-repelling quality of a sealer to stain protection. Basically, a drop of water will take considerable time to absorb into stone when the sealer has been freshly applied, because of the surface tension created by the sealer. Over some time, the surface tension will, naturally, be reduced, but this doesn’t necessarily mean the stone will be more prone to staining.
Sealer needs to be re-applied in order to retain protection. When reapplying, it’s a good idea to use the same type of sealer (assuming the correct one was selected at the start). Removing, or stripping, an existing sealer isn’t recommended.
Some final advice
Not all sealers were created equally. The quality of sealers varies, and your stone supplier will help you choose the best one for your stone, be it a water or solvent-based sealer. There are excellent options available that will help protect your marble, especially in stain-prone areas like kitchens and bathrooms. Sealers are a great investment, but only when properly selected by an experienced, project-oriented stone supplier.