What is Sealant?
You may have heard about sealants, but you may be wondering what's so special about knowing what a sealant is.
Precisely this definition will guide this subject so that we talk about products that seal structures and not go into another very close subject, which are adhesives.
So shall we understand about sealants?
As I said, the definition of sealing in civil construction can be said to work to prevent leaks, so sealants are used to seal joints or openings between two or more substrates.
The main role of a sealant is to prevent water, air, or other substances from entering or leaving the structure, even with some movement of the substrates where it was applied.
The distinction between adhesives and sealants is not always very clear, but it's worth defining this line. The purpose of the sealant is to seal a joint, and the material chosen for the sealant has the ability to move and adhere to the substrate. Adhesives, on the other hand, are materials that are designed to hold the substrates together, by joining the surfaces and are often used as an alternative to mechanical fasteners, such as screws and nails.
Some materials can be considered both sealants and adhesives and fulfill the sealing and bonding roles between surfaces. These types of materials are known as structural sealants.
All sealants must fulfill at least three main functions:
- Sufficiently fill an expansion or motion joint to create a seal between the substrates;
- Form a barrier against gases and liquids;
- Maintain sealing between structures, allowing for a certain amount of movement between parts.
History of Sealants (Brief History)
I don't want to prolong the subject too much, but I think it's interesting to present at least a historical line of sealant developments. From the first technologies that were adopted in civil construction, to the most recent.
The first sealant technology, commercialized on an industrial scale, was introduced in the early 1940s with polyisobutylene. The main applications were in civil, automotive and electrical construction.
At the end of the 1940s, the first polysulfide-based sealants were introduced to the construction markets and the aerospace industry.
A decade later, in the late 1950s, solvent-based acrylic sealants entered the construction market. This type of sealant, had one characteristic thermoplastic, different from newer acrylic technologies with characteristics elastomeric.
In the early 60's, silicone sealants entered the market. This type of sealant, with elastomeric characteristics, was and is still used in civil construction, aerospace, electroelectronic and automotive applications.
Still in the 1960s, water-based acrylic sealants and the first polyurethane sealants began to be used in construction, and polyurethane sealant gained space mainly in the automotive industry.
In the middle of the 80s, siliconized acrylic sealants appeared, which here in Brazil, are popularly known as water-based silicone sealant. At the end of the 80s, the technology of polyether-based sealants, known in our market as modified silicone-based sealant, or MS sealants, began.
The most used polyurethane sealants in Brazil today is the polyurethane technology known as hybrid, as it closes the chain with a silicone tip. This sealant technology appeared in the early 90s. At the end of that decade, polyisobutylene, also a hybrid, appeared on the market.
Here in Brazil, currently, the main chemical bases used to manufacture sealants for civil construction are polyurethane (PU), acrylic, hybrid polyurethane, polyether and silicones, both neutrally cured and acetically cured.
What Are the Types of Sealants in Brazilian Civil Construction?
Os sealants in civil construction they can be widely used in various industrial, commercial and residential applications. These applications can be done in places such as glazing, window and door seals, finishing sanitary ware in bathrooms, expansion joints on floors, facades and fire fences.
In addition to the basic function of sealing and accommodating structural movements, some specific applications may also impose additional requirements on sealants, such as vibration damping, fire fighting, electrical, acoustic and thermal insulation.
In civil construction, sealants can be classified by form, curing and hardening capacity, chemical base, performance, or final market in which they will be used. In the case of shape classification, sealants can be divided into two groups, sealants precast or preformed and sealant molded on site.
In this article we will focus on in-place molded sealants. These sealants are applied in liquid or pasty form and harden or cure at the applied site.
I will introduce basic concepts about the main sealants on the market. I will better detail each of them in separate articles, so as not to go too far into this one.
The sealants that I will introduce are, acetic silicone sealants, neutral silicone sealant, pu sealant, hybrid polyurethane sealant, ms sealant, cracked seal, acrylic sealant and water-based silicone.
Silicone Sealant
Silicone sealants for civil construction were introduced in the mid-60's and many of those sealants developed at the time are still being used today.
These sealants are available in various forms of application, from thixotropic pastes to self-leveling forms. We can also find it in monocomponent and bicomponent form.
Most of the sealants that are used in Brazil are applied and cured under ambient conditions, so they are referred to as vulcanization products at room temperature, or RTV (Room Temperature Vulcanizing). There are other special sealants, which cure when melted, known as hot melts and water-dispersion, but these are subjects for other materials.
So let's get to know more about silicone sealants?
In the Brazilian market, silicone sealants can be divided into two major classes, acetic cure silicone sealants and neutral cure silicone sealants.
Acetic Silicone Sealant
Acetic Silicone Sealant, was the first monocomponent silicone sealant developed and I'm sure you must have seen or used this sealant, am I right?
This sealant is primarily known for its characteristic vinegary odor. Because the condensation curing process releases acetic acid, the smell of this product during its curing process ends up being very striking.
Other implications of this type of cure are the applications in which the acetic silicone sealant can be used. Applications such as the encounter of glass with glass, glass with metal and metal with metal, this type of sealant is highly recommended for its high adhesion power.
On the other hand, if the metal surface does not have a protective finish, the acetic acid may attack the metal, causing corrosion and adhesive failure between the sealant and the surface.
The same adhesive failure occurs if the acetic silicone sealant is applied to cementitious surfaces in general. The acetic acid released during the curing of the sealant will react with the free calcium and magnesium hydroxides on the cement surface, causing an acid-base reaction, forming a salt and water. This salt formed at the interface between the sealant and the substrate causes the sealant to detach from the surface.
Neutral Silicone Sealant
After the acetic cure sealants were developed, other crosslinkers were used for the development of new sealants, with different characteristics and new applications where the acetic silicone sealant was not suitable for the application.
Neutral Oxymic-Curing Silicone Sealant
Neutral oxymic-curing sealants are the most common neutral sealants found in building materials stores. This type of cure has the characteristic smell of oxime released in the process.
Applications where acetic silicone sealant is not recommended, such as unprotected metal surfaces and substrates Cementícia, the neutral silicone sealant, turns out to be the best alternative.
Alkoxi Curing Neutral Silicone Sealant
Another, slightly less common, type of neutral cure is alkoxy, or alcoholic, silicone sealant. As its name says, during the curing process, the sealant releases alcohol, more specifically, methanol.
This type of silicone sealant is not found in building materials stores for sale, only in specialized distributors.
The main advantage of this silicone sealant is its high adhesion to metal surfaces, such as aluminum. The market for frames and facades in ACM ends up being the markets where this type of sealant is used.
PU Sealant - Polyurethane Sealant
The properties of polyurethane sealants are determined by the type of cure and polymers used in the formulation. Unlike silicone sealants, which use the same type of polymer, pu sealant can be formulated with a wide variety of polymers.
The standard cure mechanism is via isocyanates, however, other types of urethane polymers have been developed using different functional groups at the end of the chains, which provide other types of curing for the material.
This type of formulation was most commonly found in the Brazilian market about 5 years or more. This is due to the fact that this formulation requires the use of solvents such as xylene, heptane or acetone to adjust the viscosity and increase the extrusion rate of the sealant.
Surely you have seen or still see some polyurethane sealants being sold in metal packaging. One of the most striking characteristics of this type of sealant is the smell of the solvents used, in addition to the risk they pose in relation to flammability.
This type of sealant has been less used in recent years, due to the movement of the entire industry towards solvent-free and low COV.
Hybrid Sealant
Some newer types of sealants are based on a technology called hybrid polymers.
Basically, hybrid polymers combine the backbone of a family of sealants with reactive groups, normally positioned at the ends of the chains, of another type of polymer.
Two types of hybrid sealants used here in Brazil are, the hybrid polyurethane sealant and the ms sealant.
If you still don't know the difference between them, I've separated them below into separate topics. Look here!
Hybrid Polyurethane Sealant
O hybrid polyurethane sealant, has a different type of cure than traditional PU sealant. Two advantages of this type of molecule are greater stability in relation to exposure to the elements and also the elimination of the formation of carbon dioxide bubbles inside the cured sealant, a result of the reaction between the polyol and the isocyanate.
MS sealant
MS sealant, unlike what is said in our market, is not a sealant derived from the combination of polyurethane and silicone, but rather, a polymer known as polyether.
Just as hybrid polyurethane is a polyurethane modified with a reactive functional group, polyether, it is also modified with a reactive silicone functional group, thus MS, “Modified Silicone”.
Acrylic Sealant
Acrylic sealants are gaining space in our market, with increasingly technical applications and, in some cases, replacing other sealants in applications with little movement.
There are two major classes of acrylic sealants, water-based acrylic sealants and solvent-based acrylic sealants. Solvent-based products, which are dispersed in organic solvents, while the other is dispersed in water. In both cases, we cannot say that materials cure, since what occurs is the evaporation of the solvents present in them.
What we will discuss here will only be water-based acrylic sealants, since they are the most sold products in our market and with the highest number of applications in our buildings.
Among the acrylic sealants sold here, we can separate them into three groups, a crack seal, the acrylic sealant itself, and siliconized acrylic sealant or water-based silicone.
Each of these materials meets a specific standard, Unfortunately no ABNT so far, but with clear definitions of the movement capacity of each of these sealants.
Sela Trinca
As the name of the sealant says, the seal trinca is used to seal cracks and fissures in facades. Don't you know the difference between cracks and cracks? Take a look In this material I explained everything about this subject.
This type of material is also an acrylic sealant, often with a more rigid formulation than the other sealants. But don't take this as a negative point, it brings several benefits to this application.
Of course, it is a material that, because it is rigid, does not accompany the movement of structures like other sealants, however, for the purpose of closing or sealing cracks, it is perfect.
Because it has a formulation, in which, after drying, it will be stricter compared to other products, it will present a retrenchment smaller. Consequently, when you are going to apply the product, you don't have to go back in place and apply a second or third coat of product, as is the case with flat masses or other acrylic sealants.
Acrylic Sealant
Unlike a crack seal, acrylic sealant is an elastic material that accompanies certain movements of structures and can be used to seal door frames, meet furniture and walls, seal planned furniture, seal frames on the inside and in some cases outside.
There are in the market, from sealants for internal construction application, to high-performance acrylic sealants for outdoor application. We can classify acrylic sealants for internal use, those that meet ASTM C 834 and ASTM C 920, class 12.5 standards.
The highest performance acrylic sealants found on the market comply with ASTM C 920, classes 25 and 35. These classes already allow its use in external applications, such as sealing windows and frames.
Siliconized Acrylic Sealant - Water-based Silicone
Siliconized acrylic sealant, also known as water-based silicone, is nothing more than a high-performance acrylic sealant, additive of Silanes, which help promote greater adhesion to substrates such as concrete and metals, in addition to increasing the product's moisture resistance.
Thus, it is possible to use water-based silicone in applications where previously only silicone sealants or PU sealants were used, such as sealing gutters, ruffles, drips and also the sealing of windows and frames in buildings.
Properties of Sealants
Site-cured sealants rely on their adhesion properties to maintain a durable seal and perform the necessary functions during their lifespan. They must accommodate joint movements without failing between interfaces or in a cohesive way or causing failure in the substrates. Based on these requirements, the most important performance properties in construction sealants are movability, modulus, adhesion, and life expectancy (durability).
Structural sealings are directly dependent on the properties of the sealants chosen for the application, to maintain the perfect seal during their lifespan.
The sealant chosen for the service must accommodate the movements of the structures, without causing the three main types of faults of a sealant, which are:
- Adhesive Flaw: pathology in which the sealant completely detaches from the substrate, without leaving parts of it in the structure or bringing part of the structure with it.
- Cohesive Fault: type of failure in which the sealant adheres to the substrates but breaks in the middle of itself.
- Substrate Failure: a less common flaw to see, but it occurs when the sealant tears off part of the substrate while moving the structure.
Another type of failure that occurs a lot, in markets where price dictates the choice of products, is the degradation of the sealant due to exposure to UV, which is linked to the lifespan of the product.
Based on these requirements, we can determine the most important performance properties in construction sealants that are, the ability to move, modulus, adhesion, and life expectancy or durability.
Shore Hardness
A Shore hardness in sealants for civil construction, it represents the hardness of the material that will be used for a given application. Shore hardness has several scales, and the most common in sealants in our market is Shore A hardness.
Do you know when you are going to buy a PU sealant, for example, and you see a package with the following text on the label, “PU 40 sealant”? Well, this means the following, that the product is a sealant, chemical-based or polyurethane, with a Shore A hardness of 40.
Shore hardness is directly related to the elastic modulus of the material and, consequently, to the movement capacity.
Elasticity Modulus
The elastic modulus of a sealant describes the force exerted per unit area of a sealant under tension.
Since the primary function of a sealant is to adhere to the substrates with which it is in contact, the forces generated by an opening or closing of the joint are transmitted by the sealant to the sealant-substrate interface.
Precisely for this reason, it is important to know the elastic modulus of the sealant and also the resistance of the substrate. For example, the use of a sealant with a high elastic modulus on a “weak” substrate, such as asphalt, may result in higher tensions than the substrate supports, causing the pathology of substrate failure.
Handling Capacity
The movement capacity of a sealant is the amount of repetitive displacement that a sealant can withstand, continuously, during its useful life, without fail.
The existing specific standards only allow an assessment of the initial movement capacity of the products, but do not include the movement capacity over the years.
This means that a well-sized sealant today may not work in a few years' time, due to its natural aging, caused by exposure to weather conditions.
Adhesion to Substrates
The sealants, when applied, must develop adhesion to the substrate so that it can perform its sealing function.
Within this, three aspects are fundamental: the rate at which this adhesion is developed after applying the sealant to the joint, the level and quality of the adhesion obtained, and the durability of the adhesion.
In several applications, sealants are exposed to the natural movement of structures, which may increase the chances of it not developing rapid adhesion to the substrate and failing in the initial phase of its useful life.
Durability
Once applied, sealants are exposed to a wide variety of environmental influences and stresses.
An important characteristic of a sealed joint is the tolerance to the environment in which it will be exposed. A primary factor in sealant durability is its ability to resist degradation introduced by environmental elements such as UVA and UVB, pH, oxygen, and temperature.
Environmental and service factors of the sealant may cause degradation of the surface, volume, or interface with the substrate during its useful life.
These environmental factors can cause color degradation, shine, shrinkage, crack formation, and whitening of sealants.
Performance Standard for Sealants
Performance standards for products are essential for the evolution of the quality of the products used in the market, in addition to being documentation on which the consumer can rely to choose the most suitable product for use.
In sealants it is no different, there are two standards that are the guidelines for other regulations in different countries. These standards are restricted to sealant specifications and classifications.
ASTM C 920
ASTM C 920 - “Standard Specifications for Elastomeric Joint Sealants” is a North American standard that covers the specification of single-component and multi-component elastomeric gaskets for sealing, sealing, caulking and glazing of buildings, squares, floors, buildings, highways and airports.
ISO 11600
ISO 11600:2002 - “Building construction — Jointing products — Classification and requirements for sealants” is the standard that will most influence our sealant market. Brazil does not yet have its own performance standard for sealants, but that will change soon.
ABNT
As I said in the previous topic, for now, we do not have an ABNT standard for sealant performance. The preparation of the Brazilian NBR is in the final stages of preparation, based on ISO 11600.
Do you want to know more about sealants?
In this article I gave an overview of sealants, starting from the basic definitions of what a sealant is and a brief history about them.
After that, I separated the main types of sealants found in the Brazilian market, such as pu sealant, hybrid sealant, acrylic sealant, neutral silicone sealant, and acetic silicone sealant.
On top of each of the sealants, I explained what each of them are and a brief explanation of advantages and disadvantages for each situation found in a work.
I also went through the essential properties you need to know to choose the best sealant for each stage of your work and how to evaluate its performance over time.
Finally, I separated the main performance standards used in the world and the current situation from the Brazilian sealant performance standard.
If you have any questions regarding this issue, leave a message in the comment box below and don't forget, we're here, for any challenge.
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