Posted by The Concrete Guy on 26th Apr 2016
What Are the Different Types of Penetrating Concrete Sealers That are Available?
Two main categories exist in the concrete sealer world--penetrating and topical. First, there are topical sealers that form protective films that adhere to the top of a cementitious surface without any chemical reaction taking place between the coating and the surface. Topical coatings almost always change the surface texture by reducing the traction coefficient (i.e. slippery when wet) and also change the appearance by imparting a gloss (ex. high gloss, low gloss, satin finish, or matte finish) or color. Second, there are penetrating concrete sealers that penetrate into the capillaries of a porous cementitious surface, chemically react with it, and then create a new chemical solid that serves as a breathable barrier just below the surface being sealed but do not coat the top of the surface. These sealers usually offer a natural look and don't change the surface appearance or the surface texture. Since most penetrating sealers bond permanently with a cementitious surface, the sealers typically last as long as the substrate lasts or as long as the top of the surface to the depth of the sealer lasts.
There are four main types of penetrating concrete sealers: Silicates, Silanes, Siloxanes, and Siliconates. The Silicates are classified as densifiers and hardeners. While the Silanes, Siloxanes, and Siliconates are classified as water and/ or stain repellents. Most penetrating sealers are water based products but some can be solvent based ones. Products can vary in VOC level and solid content. Some penetrating sealers come in colors or tint packs may be available separately which can be mixed in with the sealers prior to application or be applied first and the sealer then applied as a final step. Use of colors with penetrating sealers generally produces a transparent or translucent finish as opposed to many topical coatings which can yield an opaque or monotone finish.
Penetrating sealers typically don't require much surface preparation other than ensuring the surface is clean and free of dirt, dust, debris, oil, grease, and other impurities. Unlike many topical coatings like epoxies, polyurethanes, and some acrylics, it is not necessary to profile a surface by grinding, shot blasting, sand blasting, or scarifying a surface. Surface should also be sufficiently dry though as well as porous to be a candidate for applying a penetrating sealer.
Different types of penetrating sealers provide varying degrees of densification and hardening, abrasion resistance, chemical resistance, efflorescence and dusting resistance, water and stain repellency, and overall protection. Success and performance of a sealer is usually a function of the type of substrate and type of sealer and typically requires the proper matching of the two including matching up the size of the capillaries of a surface relative to the size of a sealer molecule.
We will investigate the various types of penetrating sealers and their characteristics in this article.
Silicate Sealers are Often Used on Machine Troweled Surfaces for a Polished Appearance
If you look at the concrete floors in most big box stores or in commercial warehouses, you will find that they are most likely sealed with some type of Silicate sealer. Silicates usually consist of smaller sized molecule. Silicates react with alkalis and calcium hydroxide to form crystalline structures which "plug" the capillaries of porous cementitious surfaces. These crystalline structures are the same binder that results from adding water to Portland Cement and gives concrete much of its strength and hardness. Consequently, Silicates are commonly classified as densifiers and hardeners as the crystalline structures they form when they react with a surface serve to further densify and harden it.
The crystalline structures increase surface strength, enhance abrasion resistance, block efflorescence and dusting, and restrict absorption of water, salts, and other impurities. If the sealer is burnished into a machine troweled surface with a scrubber or polisher, this can also yield a polished appearance which can improve the look of the surface but also make the surface easier to clean and maintain. Due to its small molecular size and ability to leave a polished appearance when buffed, Silicates are generally seen as the industry standard for sealing dense machine troweled concrete floors. Controlling the depth of penetration is of particular importance with a Silicate sealer with its small molecule size and greatly affects its performance as a sealer. This is one reason why Silicate sealers often need to be applied in multiple coats, especially on more porous concrete surfaces.
Silicates are generally not considered a repellent. They do not repel water, moisture, salts, or other impurities like true repellents but instead are restricters that restrict substances from entering a cementitious surface by reducing porosity through densification. This is accomplished by the crystalline structures which are formed from the chemical reaction that takes place with a surface once a Silicate sealer is applied. The crystalline structures "plug" up the capillaries of a surface thereby reducing the porosity of the surface and hence restricting certain substances from entering into the surface. Silicate sealers are generally water based, low VOC and user and environmentally friendly.
While Silicates generally can be applied on new concrete, they cannot be used as a curing agent because they do not maintain the requisite moisture and temperature conditions that are needed on freshly placed concrete in order to properly cure the surface over a 28 day period. However, applying them on new concrete prior to it curing generally does not harm the concrete and may aid in furthering densifying, hardening, and strengthening a surface.
Three main types of Silicate sealers exist. They are Sodium, Potassium and Lithium. Here are some details about each type:
The oldest type of Silicate sealers are Sodium Silicates, which have been used since the 1930's. They are also the least expensive of all Silicate sealers. They are not as user friendly as Potassium or Lithium silicates. This is the result of Sodium Silicates often times reacting with a surface too quickly prior to full penetration into a surface. The immediate surface reaction generally also does not completely finish. This results in much of the sealer and chemical reaction taking place on the surface instead of within the capillaries of the surface. In addition, inadequate removal of the byproducts from the chemical reaction that occurs on the surface will often create a stubborn white residue on the surface that can be very difficult to remove.
To overcome these drawbacks, it is generally necessary to dampen the surface prior to applying the sealer to break the surface tension which aids in allowing the sealer to achieve better penetration before chemically reacting with the surface. Sometimes scrubbing the sealer into the surface is also needed to help achieve penetration prior to a chemical reaction occuring on the surface. After the sealer has been applied, it is also recommended to thoroughly rinse the surface to remove any unnecessary and unwanted byproducts that could result in a stubborn white residue on the surface. Due to the small size of the molecule as well as premature chemical reaction, multiple applications are usually needed.
Sodium Silicates can also raise the pH level of concrete and can force residual salts and other impurities to the surface that can also lead to a whitening on the sealed surface which is commonly referred to as surface bloom. Due to the ability to raise the pH level of a surface, they have also been linked to contributing to Alkali Silica Reaction (ASR) in certain circumstances. ASR is harmful to concrete and leads to cracking and the premature degradation of concrete. ASR is caused by a high alkali content in a surface reacting with certain types of reactive aggregate in the presence of water or moisture. This results in an expansive gel being created which if it expands enough can lead to the physical cracking of concrete.
Though more expensive than Sodium Silicate sealers, Potassium Silicate sealers tend to penetrate deeper due to a slightly smaller molecular structure than Sodium Silicates. They were developed to overcome many of the limitations of Sodium Silicate sealers. However, they did not sufficiently improve upon the Sodium Silicates and suffer from many of the same drawbacks, just to a lesser extent. Just, like Sodium Silicates, they often react too quickly with a surface prior to the sealer being able to fully penetrate into a surface and have a full chemical reaction take place in the capillaries of the surface instead of on top of a surface.
However, due to the smaller molecule size, better penetration is usually achieved with a Potassium Silicate with less reaction occurring on the surface. This lessens any surface whitening but does not eliminate it and as with Sodium Silicates is also very difficult to remove. As such, the Potassium Silicates still require the surface to be dampened to aid in penetration and reduce the possibility of a chemical reaction taking place on the surface. They also generally require scrubbing the sealer into the surface to enhance penetration and also a thorough rinsing of the surface once the sealer is applied to remove any by products that could contribute to a stubborn white residue on the surface. Due to its small molecule size as well as premature chemical reaction, multiple applications are often needed just like with Sodium Silicates.
Like Sodium Silicates, Potassium Silicates can also raise the pH level of concrete and force residual salts and other impurities to the surface leading to a whitening called surface bloom. Since pH level of a surface can be raised, Potassium Silicates have also been linked to contributing to harmful Alkali Silica Reaction (ASR) in certain conditions when high alkali concrete combines with certain types of reactive aggregate in the presence of water or moisture.
Potassium Silicates do lessen many of the issues with Sodium Silicates but do not eliminate them entirely. It is the result of the limitations of both Sodium and Potassium Silicates that lead to the development of Lithium Silicates.
Lithium Silicates are the newest Silicate technology and are also the smallest molecule size of the 3 Silicate technologies. The introduction of the Lithium Silicate technology has been one of the biggest breakthroughs in concrete sealer technology for densifiers and hardeners within the last 50 years. They are more expensive than Sodium and Potassium Silicate sealers. However, they overcome all the major drawbacks of the Sodium and Potassium Silicate sealers and are much more user friendly.
Lithium Silicates do not react as quickly with a surface like Sodium and Potassium Silicates so they are better able to penetrate a surface without any help like surface wetting and also are more easily able to facilitate a chemical reaction within the capillaries of a surface as opposed to the top of a surface. Due to its smaller molecule size, the Lithium Silicates also generally achieves better penetration than the Sodium and Potassium Silicates. The better penetration and the slower and more even and complete chemical reaction results in less, if any, whitening on the surface. If any whitening does result, it is usually limited to a fine white powder which can be easily swept away instead of a hardened residue like with Sodium and Potassium Silicates which attach to a surface and are very difficult to remove.
Lithium Silicates also do not raise the pH level of concrete. As a result, they generally do not lead to residual salts and other impurities being purged from a surface causing a whitening on the surface known as surface bloom. In addition, since Lithium Silicates do not raise the pH level of concrete, they are much safer to use on a surface than Sodium and Potassium Silicates as they cannot lead to harmful Alkali Silica Reaction (ASR) which can occur in higher pH level surfaces in presence of water and certain types of reactive aggregates.
With a Lithium Silicate sealer, there is no need to dampen the surface prior to application, scrub the sealer into to the surface to encourage penetration, or thoroughly rinse with water once sealed. Lithium Silicates are best applied by spaying onto a surface with a low pressure sprayer. Due to its small molecule size, multiple applications may still be needed. Lithium Silicates are best used on very dense surfaces like machine troweled concrete. On more porous surfaces, too many applications may be needed for it to be a practical and cost effective choice.
Silane Sealers Are Best Used for Dense Concrete, Brick, or Stone
Extremely dense concrete, brick, and stone are the best candidates for a Silane concrete sealer. Silanes are the smallest molecular structure of all reactive penetrating concrete sealers and are also highly reactive. Due to their small molecule size, Silanes are frequently used for sealing pre-cast concrete and high performance concrete such as: parking garages, building facades, and concrete forms. Silanes penetrate into a cementitious surface and form covalent bonds with minerals within the surface to create a hydrophobic and oleophobic barrier while remaining breathable.
While they do also densify and harden a surface to a degree, they are instead considered a repellent because of their excellent hydrophobic and oleophobic characteristics. As such, they do a superior job of repelling water, moisture, salts, oil, grease, and other impurities. Because of their very deep penetration, they are often used to reduce the corrosion of reinforcing steel that results from chloride exposure due to deicing salts, acid precipitation, salt air, and salt water in marine environments. They also do an excellent job in protecting against moisture from wind driven rains on the vertical exteriors of buildings. In addition, they also are superior for resisting molds, mildew, and fungus as well as protecting against freeze thaw and efflorescence and dusting.
Like all penetrating sealers, Silanes do not generally alter the appearance or texture of a substrate. Silane penetrating sealers penetrate deep into concrete, due to their small molecular size. As a result, they have low coverage rates and the surface must be thoroughly saturated, often with several applications in order to gain an adequate seal. Multiple applications, unfortunately, may darken a concrete surface. Silane sealers are generally not recommended for porous surfaces due to their small molecule size. More applications would be needed than would be practical or cost effective. The Silane technology is also the usually the most expensive of all penetrating sealers. Because of the low viscosity of Silanes, the solid content of Silanes is generally much higher (ex. 40% to 100%) than other penetrating sealers in order to compensate for such a small molecular structure.
Silanes can very in VOC level, solid content and can be water or solvent based. Water based products generally have a lower VOC and are more user and environmentally friendly. Solvent based products normally have a higher VOC and require more care in using and storing due to flammable/ combustible characteristics and solvent odor. Solvent based Silane sealers tend to penetrate more deeply than water based variants.
Silane sealers cannot be used on freshly placed concrete. Surfaces must be 28 days old and/ or fully cured prior to applying a Silane sealer.
Siloxane Sealers Are Best Used for Highly Porous Concrete, Brick or Stone
Siloxane is a derivative of the Silane family. Like a Silane sealer, they penetrate into a cementitious surface and form covalent bonds with minerals within the surface to create a hydrophobic barrier while remaining breathable. Unlike Silanes though, they are not as chemically reactive (actually, the least of all penetrating sealers) and possess the largest molecular structure of all concrete sealers. Siloxane sealers are sometimes modified with Silane sealers to form a Siloxane/Silane blend sealer, with the large molecules of Siloxane providing substantial coverage with slight penetration and the small Silane molecules providing less coverage but with deeper penetration.
Siloxanes typically work the best when you’re looking to seal extremely porous concrete, masonry, grout, mortar, stucco, and block. Because of the large molecular structure of Siloxanes, the solid content of Siloxanes is generally much lower (ex. 7.5% to 12%) than other penetrating sealers in order to compensate for such a large molecule size. Often times, Siloxanes are referred to impregnating sealers because while the molecule size is very large the sealer still penetrates and chemically reacts with a surface, just not to the extent of other reactive penetrating sealers.
While they do also densify and harden a surface to a degree, they are instead considered a repellent because of their excellent hydrophobic nature. As such, they do a superior job of repelling water, moisture, salts, and other impurities. They also do an excellent job of resisting molds, mildew, and fungus as well as protecting against freeze thaw and efflorescence and dusting. Most Siloxanes are not oleophobic and as a result do not repel oil and grease and are susceptible to permanent stains from exposure to hydro carbons such as oil, gasoline, grease, transmission fluid, and brake fluid.
Due to their large molecule size, low chemical reactivity, and shallow penetration, Siloxanes are subject to wear and weathering more so than other penetrating sealers. As such, unlike other penetrating sealers, Siloxanes typically will wear away much faster than the surface itself. Siloxane sealers have a life expectancy on horizontal surfaces of roughly only 3-5 years. As a result, they are best used on vertical surfaces if looking to optimize the lifespan of a Siloxane sealer.
Siloxanes can very in VOC level, solid content and can be water or solvent based. Water based products generally have a lower VOC and are more user and environmentally friendly. Solvent based products normally have a higher VOC and require more care in using and storing due to flammable/ combustible characteristics and solvent odor. Solvent based Siloxane sealers tend to penetrate more deeply than water based variants.
Siloxane sealers cannot be used on freshly placed concrete. Surfaces must be 28 days old or fully cured prior to applying a Siloxane sealer.
Siliconate Sealers are Workhorse Sealers that Provide the Best Water and Stain Repellence
Siliconate sealers possess a medium sized molecular structure and are a great workhorse sealer for a variety of dense or porous concrete, brick, block, stucco, or stone surfaces. Due to their medium sized molecule, they are ideal for sealing both dense and porous surfaces such as basement floors and walls, garage floors, driveways, sidewalks, porches, pool decking, patios, retaining walls, etc. While they also possess densifying and hardening characteristics, Siliconates are considered a repellent like Silanes and Siloxanes. They penetrate into the capillaries of a surface and form insoluble cross linked methyl-silicone internal membranes. The membranes are both hydrophobic and oleophobic while remaining breathable. Siliconates are fast and highly reacting and are uniquely cross linking in that the sealer bonds to a substrate as well as to itself providing the greatest repellence out of all the repellents and penetrating sealers overall.
As such, they provide the best repellence against water, moisture, salts, stains, oil, grease, and other impurities. In addition, they also provide superior resistance to molds, mildew, and fungus as well as superior protection against freeze thaw and efflorescence and dusting.
Like all penetrating sealers, Siliconates do not alter the appearance or texture of a substrate. Because of their medium molecule size and moderate penetration, they generally provide very good coverage rates and the best overall topical protection. Depending on the porosity of a surface, often times, only one application is needed and there is no need for multiple applications. Siliconates are usually water based products with zero or very low VOCs making them both environmentally and user friendly.
Siliconate sealers also make for an excellent primer or base coat to promote adhesion for topical coatings such as epoxies, polyurethanes, etc. as well as a moisture mitigation sealer prior to painting over stucco or basement walls or installing tile floors or carpeting.
One significant advantage of Siliconate sealers over other penetrating sealers is that they can be used as a curing agent and be applied onto freshly placed concrete surfaces. Other penetrating sealers cannot be used as a curing agent on freshly placed concrete and/ or a surface must be 28 days old or fully cured prior to applying.
What Are the Different Types of Topical Concrete Sealers That are Available?There are two primary types of concrete sealers—topical and penetrating. First, there are penetrating sealers that penetrate into a surface, chemically react with it, and then create a new chemical solid that serves as a breathable barrier on or just below the cementitious surface [...]