What are concrete or stone sealing compounds ?

Sealing compounds (sealers) are liquids applied to the surface of hardened concrete to reduce the penetration of liquids or gases such as water, deicing solutions, and carbon dioxide that cause freeze-thaw damage, corrosion of reinforcing steel, and acid attack. In addition, sealing compounds used on interior floor slabs reduce dusting and the absorption of spills while making the surface easier to clean.

Sealing compounds differ in purpose from curing compounds; they should not be confused as being the same. The primary purpose of a curing compound is to retard the loss of water from newly placed concrete and it is applied immediately after finishing. Surface sealing compounds on the other hand retard the penetration of harmful substances into hardened concrete and are typically not applied until the concrete is 28 days old. Surface sealers are generally classified as either film-forming or penetrating.

Do I need to seal concrete?

Sealing exterior concrete is an optional procedure generally performed to help protect concrete from freeze-thaw damage and chloride penetration from deicers. Curing is not optional when using a sealer; curing is necessary to produce properties needed for concrete to perform adequately for its intended purpose. Satisfactory performance of exterior concrete still primarily depends on an adequate air-void system, sufficient strength, and the use of proper placing, finishing and curing techniques. However, not all concrete placed meets those criteria; surface sealers can help improve the durability of these concretes.

What types of sealers can be used on concrete?

Film-forming sealing compounds  are not recommedned becasue they remain mostly on the surface with only a slight amount of the material penetrating the concrete. The relatively large molecular structure of these compounds limits their ability to penetrate the surface. Thinning them with solvents will not improve their penetrating capability. These materials do reduce the penetration of water, they also protect against mild chemicals; furthermore, they prevent the absorption of grease and oil as well as reduce dusting under pedestrian traffic.

Surface sealers consist of acrylic resins, chlorinated rubber, urethanes, epoxies, and alpha methyl styrene. The effectiveness of film-forming sealers depends on the continuity of the layer formed. Abrasive grit and heavy traffic can damage the layer requiring the reapplication of the material. Consult manufacturers’ application recommendations because some of these materials are intended for interior use only and may yellow and deteriorate under exposure to ultraviolet light.

We recommend penetrating sealers. These have been used most extensively for many years  and a new generation of water-repellent penetrating sealers have been developed with a very small molecular size that allows penetration and saturation of the concrete as deep as 3 mm.

The two most common are silane and siloxane, compounds which are derived from the silicone family. These sealers allow the concrete to breath, thus preventing a buildup of vapour pressure between the concrete and sealer that can occur with some film-forming materials. Because the sealer is embedded within the concrete, making it more durable to abrasive forces or ultraviolet deterioration, it can provide longer lasting protection than film-forming sealers. However, periodic retreatment is recommended. They are popular for protecting bridge decks and other exterior structures from corrosion of reinforcing steel caused by chloride infiltration from deicing chemicals or sea sprays.

What type of sealers should be used on natural stone?

Make sure you understand the differences between the common product types available on the market. The products typically fall into two major categories: Topical Sealer/Coatings and Impregnators.

Topical Sealers are coatings (film formers) designed to protect the surface of stone against water, oil, and other contaminants. They are formulated from natural wax, acrylic, and other plastic compounds.

Impregnators, water- or solvent-based, penetrate below the surface and become repellents. Impregnators keep contaminants out, but do not stop the interior moisture from escaping. These products are considered “breathable ,” meaning they allow for vapor transmission. They are generally hydrophobic (water-repelling), may also be oliophobic (oil-repelling)

Topical Sealers vs. Impregnators (Advantages and Disadvantages)

How do you decide whether to use a coating or an impregnator to protect the stone? Both have advantages and disadvantages. The following summary should be studied carefully to help you choose the right product. For exterior stones - Generally, topical sealers are not recommended in exterior applications, because they can trap moisture within the stone which may lead to surface deterioration during freeze/thaw cycles.

Topical Sealers

Advantages

Topical sealers are generally cheap and economical. The initial application cost is relatively small. They’re usually easy to apply. Unskilled laborers can learn to apply them with a reasonable amount of training and practice.

Topical sealers typically provide a sacrificial layer on the stone. This layer will take most of the wear on the stone. Some topical sealers can be applied below grade. These products provide various degrees of luster.

Disadvantages

Since most topical sealers are typically softer than the stone itself, they will usually scratch, mar and scuff very easily, showing traffic patterns soon after application. This will require frequent buffing, burnishing, or reapplication. Topical sealers can build up and cause an unsightly appearance, giving an unnatural, wavy, plastic look to the stone. Poor quality topical sealers can turn yellow. This is especially true if the stone is exposed to ultraviolet (UV) light.

Some topical sealers require frequent stripping and reapplication. The chemicals and abrasives used in the stripping process may cause damage to the stone. Typically, certain stripping pads and brushes can scratch softer stones. Some wax strippers can harm agglomerate stones by eating through the polyester resin binders they contain. Certain topical sealers may block the “breathing” capability of a stone. Moisture can become trapped below the surface and may lead to spalling.

Impregnators

Advantages

Most impregnators won’t change the appearance of the stone.Impregnators typically don’t require frequent applications. Since the impregnator is below the surface, it will generally last several years before reapplication is necessary. Most impregnators aren’t affected by UV light because they’re absorbed below the surface where light can’t penetrate. I

Disadvantages

Impregnators that are solvent-based produce vapors during application. In some cases these vapors can be noxious and flammable. Some water-based impregnators may also contain harmful or toxic chemicals. Always check the material safety data sheet (MSDS) of the product before deciding whether to use it.

Proper application of impregnators is generally more difficult than that of coatings. In many cases, training or professional consultation is recommended. The initial cost of most impregnators can relatively high.

Generally, impregnators cannot be used below grade to resist hydrostatic pressure. Because the stone is still capable of breathing, water can be forced through the stone by pressure.

How do you apply sealers?

Application of any sealer should only be done on stone or concrete that is clean and allowed to dry for at least 24 hours at temperatures above 16°C. At least 28 days should be allowed to elapse before applying sealers to new concrete. Penetrating sealers cannot fill surface voids if they are filled with water. Some surface preparation may be necessary if the concrete is old and dirty. Concrete placed in the late fall should not be sealed until spring because the sealer may cause the concrete to retain water that may exacerbate freeze-thaw damage.

More sealer is not better --always mop up any excess sealer in stone crevices or depressions.! Always apply in multiple even fine coats.