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The use of sealers and impregnators on granite and other stone is becoming a standard practice in our industry. With this practice comes a little controversy on the use of these products. The following are some common questions I get on this subject.

WHAT IS A SEALER, IMPREGNATOR AND PENETRATING SEALER? HOW DO THEY DIFFER?

The terminology used in the stone industry can be confusing and often misused. The following are some definitions that will help clear up this confusion;

Sealer: According to Webster’s definition, a sealer is a coat (as of size) applied to prevent subsequent coats of paint or varnish from sinking in. In the other industries, such as the cleaning and janitorial industry, a sealer is similar in that it is a coating that is placed on the surface of a substrate to seal it so something else can be applied. In the stone industry a sealer is also defined as a coating. In the scientific community the proper description is called a “Film Former” because of its application forming a film on the surface of the stone.

Impregnator: Again, according to Webster’s definition, to impregnate means to cause to be filled, imbued, permeated or saturated. In the stone industry the same definition applies. Impregnators penetrate below the surface of the stone and protect from within. There is no coating or film formed on the surface of the stone

Penetrating Sealer: A penetrating sealer is really a type of oxymoron by the pure definition of each term. If a sealer is a coating that sits on the surface then how can it also penetrate into the stone? This term however is often used interchangeably with an impregnator. Technically, you would expect that a penetrating sealer would penetrate below the material surface and also form a film on the surface of the stone. While there are products that can do both, most of the products, with few exceptions in our industry, do not.

A consolidant is another industry term worth mentioning here. This is a product that is used on stone to bind loose particles of the stone back together. These are often used on historic stone structures that become loose and brittle in a condition known as sugaring, since the fine stone particles are similar to sugar. There are numerous types of consolidants, and it is beyond the scope of this article to go into more detail; but for reference, most impregnators do not act as consolidants.

HOW DO IMPREGNATORS WORK?I

mpregnators work by reducing the pore size of the stone by filling those pores with a resin. The resins are small enough to prevent complete blockage of the pores, so the stone will still allow vapor to pass through while not allowing a liquid to penetrate. Some of the resins used are very hydrophobic and/or lyophobic. In other words they repel water and oil, depending on the type of resin used. Note that in most of the literature you will see the word appearing as oilophobic, meaning oil repellent. This is the incorrect term and this word does not exist. The proper term for oil repellent is lyophobic.

WHY IS BREATHABILITY NECESSARY?

All stone must transpire vapor. In other words, it must breathe. If a stone’s pores are totally blocked, vapor will condense within the stone and the stone will be saturated with moisture. This can lead to numerous problems such as spalling, iron oxidation, etc. The moisture can also carry soluble salts which are often deposited on the surface of the stone (efflorescence). If the salts are not allowed to escape to the surface, they will be deposited in the pores of the stone and cause deterioration.