Overview of Different Types of Penetrating Concrete Sealers

Posted by The Concrete Guy on Apr 26th 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 introducing a 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 five main types of penetrating concrete sealers: Silicates, Silanes, Siloxanes, Siliconates, and Fluorinated materials. The Silicates are classified as densifiers and hardeners. While the Silanes, Siloxanes, and Siliconates are classified as water repellents and Fluorinated materials as oil and water 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 curing agents, previous sealers, topical coatings, surface laitance, dirt, dust, debris, oil, grease, and other impurities. Unlike many topical coatings like epoxies, polyurethanes, and some acrylics, it is not usually necessary to profile a surface by acid etching, 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 oil repellency, stain resistance, 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 matching up the size of the capillaries of a surface relative to the size of the molecules of a sealer.

We will investigate the various types of penetrating sealers and their characteristics in this article.

Silicate Sealers are Often Used on Machine Troweled Surfaces or as a Polishing Aid for Polished Concrete Surfaces

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 molecules. 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, reduce dusting, and restrict absorption of water and other impurities. Depending on the smoothness of a surface, If the sealer is burnished into a surface with a floor scrubber or diamond polisher, this can often times 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 applied in the right manner, Silicates are generally seen as the industry standard for sealing dense machine troweled, burnished, or polished 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 (especially denser surfaces) 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.

Four main types of Silicate sealers exist. They are Sodium, Potassium, Lithium, and Colloidal Silica. Here are some details about each type:

Sodium Silicates

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 occurring 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.

Examples of Sodium Silicate sealers in our product offering are:

PS107 Sodium Silicate Densifier WB Penetrating Sealer (5 gal.)

PS108 Sodium Silicate w/ Siliconate Densifier WB Penetrating Sealer (5 gal.)

Potassium Silicates

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 typically 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

Lithium Silicates are the most prevalent of all the Silicate technologies and possess a much smaller molecular structure than Sodium and Potassium Silicates. 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.

Examples of Lithium Silicate sealers in our product offering are:

PS103 Lithium Silicate Densifier WB Penetrating Sealer (5 gal.)

PS104 Lithium Silicate w/ Siliconate Densifier WB Penetrating Sealer (5 gal.)

Colloidal Silicas

Colloidal Silicas are the newest Silicate/ Silica technology. They have gained a following within the last 10 years or so especially among grind/ polish contractors. They are more expensive than Sodium and Potassium Silicates but less expensive than Lithium Silicates which have seen significant price increases in recent years due to the demand for Lithium in the battery market. Like Lithium Silicates, Colloidal Silicas overcome all the major drawbacks of the Sodium and Potassium Silicate sealers and are very user friendly.

Colloidal Silica is a mixture of liquid, typically water, and silica particles. It is a colloid and not a solution like the traditional Silicates. The particles in a Colloidal Silica are measured in the nanoscale and when used as a concrete densifer typically range in size from about 5-8 nanometers up to about 50 nanometers. The particle size is controlled as part of the manufacturing process. Due to the very small particle size, Colloidal Silicas typically have greater penetration capability and higher reactivity than traditional Silicates.

Colloidal Silicas cannot be made by simply adding silica into water. Interestingly, most Colloidal Silicas are manufactured from Sodium Silicate. Through a high tech manufacturing process, the vast majority of sodium is removed from Sodium Silicate leaving behind a trace amount of sodium which acts as a stabilizing agent to purified silica that ends up suspended in a low surface tension water based fluid.

In the end, Colloidal Silicas deliver virtually pure silica particles into a surface where as the traditional Silicate densifiers not only deliver Silicate into a surface but also mineral salts (ex. sodium, potassium, lithium). This is why Sodium and Potassium Silicates typically are more involved to apply because the residual mineral salts can cause a white discoloration on a treated surface and can be stubborn to remove. Lithium Silicates overcome the issues of the Sodium and Potassium Silicates. Lithium is still a mineral salt but it is used in such a small percentage in Lithium Silicates that any mineral salt deposits left behind are negligible and not typically an issue. The only time mineral salts with Lithium Silicates are normally left behind are with significant over application and they still end up being very easy to remove. With Colloidal Silicas being about 99.5% pure silica, there are never any mineral salt deposits left behind. Over application of a Colloidal Silica can result in the silica drying on the surface and leaving behind loose, dry, brittle silica deposits (ex. sand) that can normally be easily swept away.

In addition to being used as a floor densifier and hardener or as a polishing aid for polished concrete surfaces like traditional Silicates, Colloidal Silicas have recently begun to be used as a troweling aid or curing aid for freshly placed concrete. The Colloidal Silica extends the finishing time (especially in hot, dry, windy conditions), makes troweling much easier, eliminates the need to add excess water, and also adds to strength and durability of top layer of the surface. When used as a curing aid, Colloidal Silicas allow for the proper hydration of concrete by reducing rapid water evaporation while retaining breathability. They are easier, more efficient, and less costly to apply than traditional curing agents or methods and also become a permanent part of the concrete itself. They do not interfere with the subsequent application of penetrating sealers, the bonding of topical coatings, or the adhesion of glues or mastics used in floor coverings and thereby eliminate need for costly and labor intensive mechanical or chemical removal of more traditional film forming curing agents.

Colloidal Silicas have a pH less than traditional Silicates so they do not raise pH level of concrete and do not contribute to Alkali Silica Reaction (ASR) which can occur in higher pH level surfaces in presence of water and certain types of reactive aggregates .

While Colloidal Silicas certainly possess many advantages, they are not without their limitations. Since there is very little stabilizing agent (ex. sodium) in Colloidal Silicas, they are inherently far less stable than traditional Silicates. As such, Colloidal Silicas can more easily lose their stability where the silica will precipitate and permanently fall out of the solution rendering them unusable. This can happen in a number of scenarios:

  • Temperature extremes either extreme hot or cold
  • pH is altered by addition of certain surfactants or other chemistries often added to traditional Silicates (ex. Siliconate) to otherwise improve performance
  • Very small particle size (ex. 5nm) Colloidal Silicas eventually begin to lose their charge and become unstable

Due to the instability issues, most Colloidal Silicas are sold as concentrates. In concentrate form, Colloidal Silicas tend to be more stable. With Colloidal Silicas being sold as a concentrate instead of coming prediluted as is customary with the traditional Silicates, it can sometimes cause issues at job sites where there is not access to clean water or where the Colloidal Silica is not diluted down properly by addition of either too much or too little water. For best results, it is also highly recommended that distilled or deionized water be used for dilution of Colloidal Silicas but that is almost never a practical option at a job site. Colloidal Silicas also often possess a much shorter shelf life than standard silicates, in some cases, only 6 months requiring them to be used within a short period of time after purchase  or end up unnecessarily disposing of unused material.   

Silane Sealers Are Best Used for Dense Concrete & Masonry

Extremely dense concrete and masonry are the best candidates for a Silane concrete sealer. Silanes have a very small molecular structure and also are slow reacting which together allow for deeper penetration into a surface. Due to their small molecule size, Silanes are frequently used for sealing pre-cast concrete and high performance concrete such as: parking garages, bridge decks, building facades, and concrete forms. Silanes penetrate into a cementitious surface to form cross linked silicone resinous membranes within the surface while remaining breathable.

Silanes are considered a water repellent and they possess excellent hydrophobic characteristics. As such, they do a superior job of repelling water, moisture, salts, dirt, 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 mold, mildew, and fungus as well as protecting against freeze thaw and efflorescence.

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 expensive relative to other penetrating sealer chemistries. Because of the very 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 and the loss of actives due to fast evaporation.

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.

Examples of Silane sealers in our product offering are:

PS105 Silane Water Repellent WB-40 Penetrating Sealer (5 gal.)

PS109 Silane Water Repellent SB-100 Penetrating Sealer (5 gal.)

Siloxane Sealers Are Best Used for Highly Porous Concrete, Brick or Stone

Siloxane is a derivative of the Silane family. Like a Silane sealer, a Siloxane penetrates into a cementitious surface to form cross linked silicone resinous membranes within the surface while remaining breathable. Siloxanes possess the largest molecular structure of all penetrating concrete sealers and are also the least chemically reactive. Siloxane sealers are sometimes modified with Silane sealers to form a Siloxane/Silane emulsion, 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. 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.

Siloxanes are considered a water repellent because of their excellent hydrophobic nature. As such, they do a superior job of repelling water, moisture, salts, dirt, and other impurities. They also do an excellent job of resisting mold, mildew, and fungus as well as protecting against freeze thaw and efflorescence. 

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 3-5 years. They are often used on vertical building exteriors so the lifespan of the sealer can be further optimized.  

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.

Examples of Siloxane sealers in our product offering are:

PS110 Siloxane Water Repellent WB Penetrating Sealer (5 gal.)

Siliconate Sealers that Can be Used on a Variety of Smooth or Rough Concrete Surfaces

Siliconate is a derivative of the Silane family. Siliconate sealers possess a medium sized molecular structure and are a great workhorse sealer for a variety of dense or porous concrete, block, stucco, mortar, and grout surfaces. Due to their medium sized molecule, they are ideal for sealing both dense and porous surfaces such as warehouse floors, shop floors, garage floors, driveways, sidewalks, porches, pool decking, patios, retaining walls, etc. Siliconates are considered a water repellent like Silanes and Siloxanes. Siliconates penetrate into a cementitious surface to form cross linked silicone resinous membranes within the surface. The membranes are hydrophobic while remaining breathable. 

As such, they provide excellent repellence against water, moisture, salts, dirt, and other impurities. In addition, they also provide superior resistance to mold, mildew, and fungus as well as superior protection against freeze thaw and efflorescence. 

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.

Certain 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. Surfaces still need to satisfy the profile requirements (ex. through acid etching, diamond grinding, etc.) for the topical coating that is applied over the Siliconate sealer. 

One significant advantage of certain Siliconate sealers over other penetrating sealers is that certain ones can be used as a curing agent and be applied onto freshly placed concrete surfaces. Other penetrating sealers generally 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.

Examples of Siliconate sealers in our product offering are:

PS101 Siliconate Water Repellent WB Penetrating Sealer (5 gal.)

PS102 Siliconate Water Repellent WB Penetrating Sealer (5 gal.)

Fluorinated Sealers for Water and Oil Repellence and Maximum Stain Resistance

Fluorinated sealers are a new bread of concrete sealers. They are uniquely both hydrophobic and oleophobic and offer improved stain resistance. However, Fluorotechnology has a very long history in a wide variety of applications. Fluorine has been used extensively for decades in grease resistant food packaging (ex. pizza boxes), non stick cookware, high performance rainwear and outdoor gear, and stain resistant carpeting and fabrics. A couple of very notable household brands which are based on Fluorochemistry are Teflon and Scotchgard. Fluorosurfactants have also been used for years in paints, coatings, and floor finishes to improve wetting, penetration, leveling, and dry film appearance. They have also been used in adhesives, sealants, and caulks to strengthen bonds with surfaces and to improve overall durability.

Fluorinated materials are a very expensive chemistry and until recently they were only used in smaller amounts as an additive, if even used at all, to water repellents (ex. Silanes and Siloxanes) within the building materials industry to render them not only hydrophobic but also oleophobic. With recent advances in Fluorochemistry and the ability to engineer formulations with a higher Fluorine content but at lower active total solid concentrations, there is now a way to make more cost effective (but yet still expensive) Fluorinated sealers without the added cost of using other materials like Silane and Siloxane as part of the formulation.

Fluorinated materials are known for having extremely strong Carbon-Fluorine bonds which are very stable and nonreactive. These bonds are more durable, long lasting, UV resistant, and heat resistant than that of traditional water repellent sealers like Silanes, Siloxanes, and Siliconates. Fluorinated sealers penetrate and absorb into a substrate and chemically react with it to physically and chemically bond with a surface. The molecules in Fluorinated sealers are extremely small nanosized particles and offer excellent penetration even in very dense but yet still porous cementitious surfaces.

Fluorinated sealers are used to impart both water and oil repellent characteristics to a surface. They are also used to combat freeze/ thaw, efflorescence, mold/ mildew, and dirt buildup. These sealers also offer the most stain protection out of all penetrating type sealers. The level of stain resistance is typically only surpassed by the use of topical sealers/ coatings. They provide reasonable opportunity to clean up most accidental spills. These products will eliminate or at least significantly reduce most common staining. They also make surfaces easier to clean and maintain and keep surfaces looking cleaner for longer.

Fluorinated sealers, like most penetrating sealers, generally do not alter the appearance or texture of a substrate. Because of their very small molecular structure, they offer excellent surface penetration. Due to their small molecule size, these sealers are most effective on dense surfaces like machine troweled concrete, porous natural stone, cement terrazzo, grout, and mortar. When used on appropriate denser surfaces, they can offer very good coverage rates. Depending on the porosity of a surface, often times, only one application is needed. Fluorinated sealers are usually water based products with very low VOCs making them both environmentally and user friendly.

Most Fluorinated sealers cannot be used on freshly placed concrete. Surfaces must be 28 days old/ or fully cured prior to applying a Fluorinated sealer.

Examples of Fluorinated sealers in our product offering are:

PS100 Fluorinated Water, Oil & Salt Repellent WB Penetrating Sealer (1 gal.)