Should Natural Stone Be Sealed?
From The Marble Institute of America
In some cases it makes perfect sense to seal the stone. Once properly sealed, the stone will be protected against everyday dirt and spills. In other cases, it is best to leave the stone untreated. Topical sealers can alter the surface texture and finish, as well as build up on the surface creating a layer that is less durable than the stone.
Marble Institute of America Statement of Position On Sealing Natural Stone Countertops
Most granite countertops do not need to be sealed. Before 1995 there were very few quality penetrating sealers on the market and there were very few cases of staining. Both prior to and after the availability of penetrating sealers, no cases of food poisoning, radon, or food preparation issues associated with treated or untreated granites have been reported. If a homeowner cleans their countertops after each meal, they will rarely, if ever, have staining or cleanability issues with granite. All this being said, many granite countertops receive additional benefit from being sealed. That benefit is the further reduction of moisture migration into an already moisture resistant surface.
Should natural stone counters be sealed? In many cases it makes sense to seal marble and granite countertops with a quality sealer. The product should have a life expectancy of ten to fifteen years and be of an oliophobic (resistant to water and oil based stains) nature. Once properly sealed, the stone will be more resistant against everyday dirt and spills.
In today’s natural stone industry, many species of granite receive a resin treatment at the factory where the blocks of granite are cut into slabs and then polished. The treatment is used to fill microfissures, indentations and other minor characteristics that are found in many natural stones. The reason for the resin treatment is to address what most consumers consider as imperfections, but in reality are “birth marks”. The consuming public gravitates to perfection, defined as no “birth marks,” and so the marble and granite industry tries to fulfill the desire. Both resined as well as unresined slabs will outlast most of our lifetimes. Granite should, and in most cases will, be the last countertop surface a person will buy, providing a strong return on investment. The bottom line: Sealing resin treated countertops may increase the resistance of the already resistant nature of stone (adopted 11/8/06).
Dimension Stone Design Manual, Version VII, page 3-5, 3-6
Factors to consider prior to determining if the stone should be protected:
What is the hardness, density, and durability of the stone?
The type of stone, its finish, its location, and how it is maintained all need to be considered when determining how to protect the stone. The MIA recommends that these factors be reviewed with the end-user during the decision making process.Different types of Products
Make sure you understand the differences between the common product types available on the market. The products typically fall into two major categories: Topical Sealer/Coatings and Impregnators.
Topical Sealers are coatings (film formers) designed to protect the surface of stone against water, oil, and other contaminants. They are formulated from natural wax, acrylic, and other plastic compounds. Coatings are classified into two general types: strippable and permanent:
Strippable coatings are formulated to be easily stripped or removed from the stone. These coatings are made of polymers such as acrylics, styrene, and polyethylene, and are usually water-based. Many of the janitorial coatings available on the market are water-based, polymer-type products designed for resilient tile floors and not for stone. Read the label carefully and/or consult with the Manufacturer prior to application.
Permanent coatings, once applied, are very difficult to remove. They’re made of solvent-based or water-based polymers such as polyurethane and epoxies. These are not normally recommended for stone.
When a topical sealer is applied, the maintenance program often shifts from a program focused on the stone care to a program focused on the maintenance of the sealer (for example: stripping and reapplication).
If a coating is used on a countertop where food is to be used, verify the coating is approved for food use.
Impregnators, water- or solvent-based, penetrate below the surface and become repellents. Impregnators keep contaminants out, but do not stop the interior moisture from escaping. These products are considered “breathable ,” meaning they allow for vapor transmission. They are generally hydrophobic (water-repelling), may also be oliophobic (oil-repelling):
Hydrophobic impregnators are formulated to repel only water and water-based chemicals. Fruit drinks, coffee, tea, and soda, for example, would be repelled by a hydrophobic impregnator.
Oliophobic impregnators are designed to repel water and oil-based liquids. Cooking oil, grease, and body oils are examples of substances that would be repelled by an oliophobic impregnator.
An important distinction between oliophobic and hydrophobic impregnators is that an oliophobic impregnator is always hydrophobic, but a hydrophobic impregnator may not be oliophobic. Be sure to read sealer product labels carefully or contact the Manufacturer to determine if they are hydrophobic, oliophobic, or both.
Some products are also labeled as “oil-resistant,” but “oil-resistant” and “oil-repellent” are entirely different. An oil-resistant impregnator will only slow down the absorption of oil into the stone. An oil-repellent impregnator will prevent oil from entering the stone. Make certain that you’re buying the appropriate product for your particular application.
Topical Sealers vs. Impregnators (Advantages and Disadvantages)
How do you decide whether to use a coating or an impregnator to protect the stone? Both have advantages and disadvantages. The following summary should be studied carefully to help you choose the right product.
Topical Sealers – Advantages
Topical sealers are generally economical. The initial application cost is relatively small.
Topical Sealers – Disadvantages
Since most topical sealers are typically softer than the stone itself, they will usually scratch, mar and scuff very easily, showing traffic patterns soon after application. This will require frequent buffing, burnishing, or reapplication.
Impregnators – Advantages
Most impregnators won’t change the appearance of the stone.
Impregnators – Disadvantages
Impregnators that are solvent-based produce vapors during application. In some cases these vapors can be noxious and flammable.
Some varieties of solvent-based impregnators are harmful to the environment, releasing large amounts of volatile organic compounds (VOCs). For this reason, the use of these impregnators is restricted in certain states. Also, some water-based impregnators may also contain harmful or toxic chemicals. Always check the material safety data sheet (MSDS) of the product before deciding whether to use it.
Other Factors to Consider
Exterior stones - Generally, topical sealers are not recommended in exterior applications, because they can trap moisture within the stone which may lead to surface deterioration during freeze/thaw cycles.
Resined stones - In some situations, impregnating sealers applied to a resined stone will cause the material to cloud, discolor, or fade. While this is a new topic in the stone industry, some initial reports have indicated that the application of a color enhancer may hide the problem. Additionally, the problems have occurred with solvent-based vs. water-based impregnators. It is highly recommended that you consult with the Sealant Manufacturer prior to applying a sealer to a resined stone.
Staff Education - How well does your staff understand the differences between sealers? Consider holding a training session on this topic. Some questions your staff should be able to answer include
What are differences between a topical sealer and an impregnator? What are the advantages vs. disadvantages?
Consumer Education – When discussing the pros and cons of sealers and/or impregnators with your consumers, advise the consumer to:
Carefully review the ‘factors to be considered’ prior to treating (checklist from page 1).
Careful review of multiple factors (i.e. type of stone, its finish, its location, and how it will be maintained) be taken into consideration when determining how to protect the stone.
This technical bulletin contains general guidelines. The Marble Institute of America and its Member companies are not responsible for any use or misuse that causes damage of any kind, including loss of rights, materials, and personal injury alleged to be caused directly or indirectly by the information contained in this document.
The MIA thanks MIA Member firms The National Center for Stone & Masonry Trades, Aqua Mix Inc., StoneTech Professional Inc., Miracle Sealants & Abrasives Company, as well as members of the MIA Board of Directors, Education Committee, and Technical Committee for their help and advice.
Copyright © 2007 Marble Institute of America
This information may be updated periodically.