DO you Need to Seal your Marble, Granite or other Porous Stones?

Published: 09th April 2009
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The answer is YES. All Stone surfaces need to be sealed. However many factors need to be considered when choosing the correct sealer. First, the type of stone. All stone is not created equal. How porous a stone is and how fast it absorbs liquids is called the absorption coefficient. This coefficient is extremely important when choosing a sealer. Granite generally will have a higher absorption coefficient than a polished marble. Limestone can be extremely absorbent. The higher the absorption coefficient, the more difficult it will be to seal the stone.

To get a general idea of how absorbent the stone is, place several drops of water on the surface of the stone and time how long it takes for the water to completely disappear. If the water disappears in under one minute, consider the stone very porous. If it take up to 3-4 minutes, consider it porous. If it takes more than 5 minutes, consider it slightly porous. This simple test will also give a good indication of the quantity of sealer needed to protect the entire area.

How do we protect stone and other porous materials from staining. There are so many sealers on the market today. Which ones are best? Which ones really work?

It can be very confusing trying to choose a sealer to protect stone. In the past several years, the stone restoration and janitorial industries have bombarded the market with hundreds of products to seal, protect and polish stone.

Fortunately, all of these products fall into only two major categories:
1. Coatings
2. Impregnators or penetrating sealers.

Coatings are sealers that place a sacrificial coating on the surface of the stone. This is a film that lays on top of the stone acting as a barrier to prevent water, oil and dirt from entering the pores of the stone. Coatings can be classified into two general types: 1. Strippable, 2. Permanent.

How do you make the determination between a coating or an impregnator?
They both have their advantages and their disadvantages. The following
summary should be studied carefully when choosing the proper product:

Coatings are sealers that place a layer on the surface of the stone.
1. Coatings are generally economical. The initial application is relatively low cost.
2. Coatings are generally easy to apply. Unskilled labor can learn to apply them in a short time.

1. Since most coatings 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 re-application.
2. Coatings can build up and can cause an unsightly appearance, producing an unnatural, wavy, plastic look to the stone.
3. Poor quality coatings can turn yellow. This is especially true if the stone is exposed to UV light.
4. Coatings require frequent stripping and reapplication. The chemicals and abrasives used in the stripping process may cause damage to the stone. Typically, certain stripping pads and stripping brushes can scratch some softer stones. Some wax strippers can harm certain stones such as agglomerates, eating away at the polyester binders.
5. Certain coatings may block the breathing capability of the stone. Moisture can become trapped below the surface and may lead to spalling.

1. Most impregnators will not change the appearance of the stone.
2. Most impregnators do not require frequent applications. Since the impregnator is below the surface, it will generally last several years before reapplication is necessary.
3. Most impregnators are not affected by UV light since they are below the surface where UV light cannot penetrate. For this reason they can be used outdoors.
4. Impregnators are typically hydrophobic, while some are oiliophobic.
5. Floors that have been impregnated are easier and less expensive to maintain than non-impregnated or coated floors because the stone is harder than the coatings.

1. Impregnators that are solvent-based smell bad and are flammable during application.
2. Solvent-based impregnators are harmful to the environment producing high VOC (volatile organic compounds).
3. The initial cost of most impregnators is relatively high.

When choosing the proper product for protection, the above guidelines should help. Always talk with the manufacture or distributor, and let them know where you plan to use their product. They can be very helpful if you tell them all the conditions that apply.

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