Frequently Asked questions about sealers, penetrating
sealers and impregnators
By Frederick M. Hueston
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.
Q. 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," since when applied it forms 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 filmed formed on the surface of
the stone.
Penetrating Sealers- Penetrating sealer is really a type of oxymoron if we go
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 interchangeable with an impregnator. Technically you would expect
that a penetrating sealer penetrated below the surface and also forms a film on
the surface of the stone. While there are products that can do both, most of
the products, with few exceptions our industry do not.
Some other terms used in our industry are also worth mentioning:
Consolidents- A consoildant is a product that is used on stone to bind loose particles of the stone back together. In otherwords to glue loose stone together. These are often used
on historic stone structures that become loose and brittle. A condition known
as sugaring, since the fine stone particles are like sugar. There are numerous
types of consolidants and it is beyond the scope of this article to go into
more detail. Most impregnators do not act as consolidants.
Q. How do impregnators work
Impregnators work by reducing the pore size of the stone by filling the 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: in most of the literature you will see the
word Oilophobic, meaning oil repellent. This is the incorrect term and this
word does not exist. The proper term for oil repellent is Lyophobic.
Q. 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.
Q. What types of impregnators are there?
Impregnators can be broken down into several categories. They can be water
based or solvent based. Most impregnators also contain one of two main
ingredients: Silicon derivatives or fluoro alphatics. In generally the silicone
types repel water and the fluoro types repel both water and oil. Many companies
are going to strictly water based formulas due to the fact that they are safer
to use, have little order and are better for the environment.
Q. Are sealers safe for food handling areas?
This will all depend on the manufacturer. Generally once the impregnator has
dried and cured it should be safe for most food handling situations. However,
to be sure check with the products manufacturer.
Q. What problems do you see with impregnators
The problems I have seen to date are few and almost always caused by
misapplication of the product. If the impregnator is left on the surface of the
stone and the excess is not removed, it can cause the stone to be sticky,
making removal difficult.
Recently I have seen some solvent based impregnators reacting to resined slabs
causing clouding or discoloration.
Another problem is applying an impregnator to a wet stone. If the stone is wet,
the impregnator will not penetrate and hence it wont perform as expected.
Overall, most impregnator are trouble free.
Q. How often must an impregnator be applied
This will also depend on the type and use of the stone. I generally recommend
that they be applied about once per year. More frequently applications may be
necessary for commercial applications.
Q. Does all stone need to be sealed?
This is an ongoing debate in the industry. There are those who say that all
stone needs to be sealed and others who say that only some very porous stone
needs sealing. The best test is to perform a simple absorbency test as follows:
Place about a teaspoon of water on the stone surface and allow it to sit for
one to two minutes. If the stone becomes dark under the water, which indicates
that it is absorbent, then the stone will need to be sealed.
Q. Are sealers and impregnators UV resistant?
Again, this will depend on the type. In general, since they work below the
surface most will be UV resistant. Remember that UV light is very powerful and
will eventually have an effect on any sealer or impregnator. Most topical sealers are not UV resistant and
will discolor over time.
The above information is based on current knowledge, but one must be aware that
the chemistry of impregnators and sealers can and will change. My best advise
is to keep up with current trends and ask lots of questions when looking into
any new product.
Frederick M. Hueston
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