Concrete sealers

Concrete sealers are coatings applied to concrete to protect it from corrosion. They either block the pores in the concrete to reduce absorption of water and salts or form an impermeable layer which prevents such materials from passing.^[1]

Extensive research from concrete authorities in North America – American Concrete Institute, Portland Cement Association, National Ready Mix Concrete Association - confirm that almost all damage to concrete is attributable to moisture intrusion: alkali-silica reaction (ASR), chemical intrusion, freeze/thaw, and corrosion of reinforcements.

For decades attempts to protect concrete from moisture intrusion have included sealers ranging from wax to linseed oil. Today, all high quality sealers can block surface moisture which can transmit damaging chemicals and induce freeze/thaw damage. There are two main sealer categories: topical sealers (film-forming) and penetrating sealers (reactive).

Topical sealers generally provide visual enhancement as well as topical protection. They require dry, clean surface during application to gain adhesion. Life span is generally 1–5 years.

Penetrating sealers can be applied to dry or damp surfaces and should be properly matched with substrate porosity in order to penetrate the surface, clot, and form a barrier. Penetrating sealers generally do not significantly modify substrate appearance. They are chemically reactive and bond with minerals in cement reducing the amount of free silica available for ASR and reduce moisture required to induce ASR. As well as blocking surface moisture they block subterranean moisture and can reduce efflorescence. Lastly, penetrating sealers can harden and increase the density of concrete, increasing its strength as measured in pounds per square inch (PSI). The Lifespan of these sealers can be nearly permanent.^[2]

Today, five major compounds are commonly used in concrete sealers:

Acrylic resins form a topical thin film membrane. Acrylics are affordable and generally simple to apply. They are well known to increase perceived visual enhancement and generally provide good UV protection for colored substrates. They can make substrates slick when wet, sometimes requiring the addition of anti-skid materials. Despite being the softest and least lasting of the major sealer categories, price and convenience make acrylics a very popular choice for residential applications such as stamped concrete and exposed aggregate.

Epoxy/urethane systems are also topical film-forming membranes. They share many of the same characteristics as acrylics, but the performance levels and life span are superior and commensurately they are more costly. Epoxy/urethane systems are frequently used in demanding applications such as factory floors, garage floors, and restaurants. Water-based versions are often used to seal concrete counter tops.

Silanes are the smallest molecular compound of penetrating sealers. Generally expensive, 100% silane versions offer high standards of performance in high-value applications with substrates of limited porosity, such as parking garages, slate, blue stone and other valuable materials.

Silicates are another small molecular compound frequently used for sealing substrates of moderate porosity. They are ideal for sealing substrates such as factory floors, retail show rooms, garage floors and basements. When burnished, premium silicate blends such as lithium silicates can help concrete develop a polished appearance popular in many large format retail outlets and home centers. Plain silicates are low in cost, and as such are often misapplied as a sealer for porous, broom finished substrates such as driveways. This is a poor use of the chemistry, as the liquid disperses randomly without forming a substantial protective barrier.

Siliconates are the largest molecular compound of truly penetrating sealers. While relatively expensive, they are the ideal molecular compound for sealing highly porous substrates such as driveways, sidewalks, parking lots, stucco, foundations, concrete block, many types of natural stone and artificial stone, and mortar. Siliconate and organo-siliconates have also been shown to be highly effective as curing agents for new concrete.

Siloxanes and silicones are sometimes described as penetrating sealers. However, neither compound is highly chemically reactive, a trait of a true penetrating sealers. Additionally, both are large molecular compounds which provide predominantly topical protection. Because these materials remain predominately at, or near, the surface the benefits are not as long lasting as properly applied silane, silicates or siliconates. When blended with silanes, siloxanes are an effective sealer for vertical surfaces where surface wear is not a major factor. Because of their slickness, silicones are generally used in vertical applications as moisture and graffiti barriers.

Several of the above listed sealers can be used in combination. Silanes, silicates and siliconates, which must be applied directly to the substrate, can be very receptive to topical coatings and can be used first in a multi-component system, followed by acrylics or epoxy/urethane systems. Silicates can also be applied as a second step with siliconates as the smaller molecules can provide additional pore closure. Siloxanes and silicones are too topical in nature to be reliably used on conjunction with topical coatings.

References

1. ^ Caijun Shi, Y. L. Mo (2008), High-performance construction materials, p. 335, ISBN 9789812797353, http://books.google.com/?id=pWkxjs1vAqMC 
2. ^ Pat Motz, Concrete Sealing Tips.com (2010, Concrete Sealing Issues, http://concretesealingtips.com/concrete-issues-scaling-spalling-effloresence-etc/