Until the middle of the last century, rubber or cork were mainly used to seal various joints in engineering and seal joints in construction. These were expensive materials, and they needed to find a cheap alternative, an adhesive substance that could be produced in virtually unlimited quantities using available inexhaustible resources.
The first experiments on the synthesis of polyamides began in the United States, but the German scientists who soon joined the problem were more fortunate than the American researchers: they were able to obtain polyurethane elastomers by combining polyols with some diisocyanates. Later, as a result of various experiments, polyurethanes known today were created.
Why polyurethane sealant has become such a popular building material?
This is due to the fact that the sealant is polyurethane based:
- possesses extremely high elasticity (sometimes reaching 1 000%);
- demonstrates excellent adhesion to many materials, including concrete and bricks, metal, wood and glass;
- has excellent self-adhesion;
- resistant to moisture and ultraviolet radiation;
- provides high-quality sealing and waterproofing of structures for a long time;
- can withstand negative temperatures up to -60 ° C;
- can be used when working in the winter, if the ambient temperature does not fall below -10 ° C;
- does not flow (if the thickness of the applied layer is less than one centimeter) from the vertical planes of the structures;
- gives zero shrinkage after polymerization;
- dries quickly and hardens;
- may be colored or transparent;
- does not emit harmful substances after solidification (and therefore it can be used in bathrooms, in kitchens, and in living rooms);
- polymerized by the action of moisture in the air.
However, the polyurethane sealant offered by manufacturers today has its drawbacks. The main ones are listed below.
- Its adhesion is not sufficient to ensure a reliable strong connection and good sealing of the seams of products, the material of which are some types of plastics.
- Polyurethane sealant should not be applied to surfaces whose moisture content exceeds 10%. In this case, to increase adhesion, you must use special primers.
- It loses its qualities upon prolonged exposure to temperatures in excess of 120 ° C.
- Disposal of polymerized polyurethane sealant is an expensive, complex manufacturing operation.
What else can you say about the technical characteristics and features of the use of polyurethane sealant for sealing seams?
Since the sealant based on polyurethane, presented on the market by both domestic and foreign manufacturers, has many advantages, it is used in various fields of human activity. Most often it is used in the construction industry for embedding seams of deformation nature or gaps in concrete structures and as a sealant for wood. Such material well seals the roof, windows, the joints between the logs. It is also suitable as an elastic sealant for joints in a wooden house, as it has high adhesion to wood, and for sealing into the bathroom.
One of the distinguishing qualities of polyurethane sealant is that it seals even the suture joints, consisting of materials of various types, that is, significantly different in chemical composition and physical properties.
This sealing building material is very economical in consumption. For example, if it is necessary to close a suture gap of 10 millimeters in depth, the sealant consumption in this case is only 100 ml / m.
When choosing a sealant for a wooden house or for concrete structures, or if waterproofing with a polyurethane sealant for a bathroom is required, you should familiarize yourself with its technical specifications on the manufacturer’s packaging, including its important property, such as hardness. Since it depends on it the ability of sealing joints to resist shrinkage and deformation.
Sealing compounds with a hardness of 15 units are used for sealing joints in panels made of concrete, slots in the roof. This polyurethane sealant is also suitable for gluing parts made of wood, glass, metal, plastic.
With a hardness of a sealing substance of 25 units, it can seal joints that experience a constant effect of moisture. If the hardness is 40 units, then such a sealant is most suitable for glass, as well as for performing work related to the need to seal and seal the construction temperature joints of reinforced concrete structures.
The presence of a polyurethane sealant hardness of 50 units, makes it possible to use it in sealing metal products. The highest possible level of hardness is 60 units. Such sealants are used in industries related to the automotive and shipbuilding industry.
After opening a package containing a sealant, its contents should be immediately used for its intended purpose, and it should be applied in such a way that the thickness of the seam does not exceed 0.5 cm. In this case, you can achieve reliable sealing with a sufficiently economical expenditure of adhesive material.
Other areas in which polyurethane-based sealants are used
When installing door / window constructions, all joints are sealed with their help.
In the jewelry industry, the use of polyurethane sealants (especially transparent) for fixing natural stones provides barely noticeable neat joints. And since this material is produced in different colors, it is easy to find such a shade of it that will be very close to the color of the stone used in the decoration. The use in this case of silicone-based (even transparent) sealant is unacceptable, because the latter can not only change the color of a precious or semi-precious stone, but also destroy it over time.
In those places of structures, in which there are significant vibrations, it is better to use polyurethane sealants, which are not prone to shrinkage and change in shape. That is why they are often used in the automotive industry.
If it is necessary to perform suture joints exposed to significant temperature changes, the use of a polyurethane sealant is also recommended, as it is also very elastic and resistant to punctures and abrasion.
In the case of waterproofing works for a bathroom, in a fountain, in external ponds or on the roof, a polyurethane sealant suitable for its technical properties can also be successfully used. After curing, the layer of polyurethane has a sufficient density to ensure its resistance to moisture.
Types of polyurethane sealants
Polyurethane based adhesive can be either one component or two component.
One component sealant
It is a pasty substance, the main component of which is a polyurethane prepolymer. Such a single-component polyurethane adhesive has a high adhesion to most building materials. It meshes well with ceramics and glass. After applying this one-component sealant at the joints, the process of its polymerization begins due to exposure to moisture contained in the ambient air.
Single-component compositions are easy to use, as it does not require mixing of any components, which ensures guaranteed quality of joints. Such sealants can be used for both repair and construction work, and in particular for sealing:
- building structures;
- roof joints;
- car bodies;
- installed in the car windows.
In this case, the sealants used in the latter case are often referred to as glass. They are used when performing operations on pasting autoglasses and when installing fiberglass decorative elements in automobiles, as well as when you need to firmly glue glass or plastic parts to a metal base that constantly experiences strong vibrations, temperature changes, water and moisture during operation. .
The disadvantage of one-component compositions is that they cannot be used at an ambient temperature of less than -10 ° C because:
- as the temperature decreases, the humidity of the air decreases, and, as a result, the rate of glue polymerization decreases;
- an increase in the hardening time of the sealant ultimately leads to a decrease in its elasticity, adhesion and hardness;
- due to the increase in viscosity of a single-component polyurethane adhesive under these conditions, the work associated with its use is complicated.
Two component sealant
In the package of such polyurethane glue there are two separately packaged components:
- a paste containing polyols;
- special hardener.
As long as the substances are not mixed, they can be stored for a long time, since they do not interact with the environment.
The main advantage of two-component sealants is that they can be used at negative temperatures, since when they freeze, the moisture contained in the air does not participate in this process. At the same time, these compounds, as well as the one described above, provide strong, elastic and durable seams.
Of the minuses can be noted that:
- it takes some time to mix the components, which leads to an increase in the total time allotted for the work;
- the quality of the seams created depends on how correctly the proportions of the ingredients were chosen when they were mixed;
- prepared glue should be used immediately after mixing.
When comparing two-component polyurethane formulations with one-component formulations, it can be concluded that, due to the greater ease of use of the latter for domestic use, it is better to purchase one-component glue.
In the construction area, a special polyurethane sealant for concrete is often used, which does not contain solvents. Its popularity among builders is due to the ease of use and the high quality of the seams it creates. This is an excellent polyurethane sealant for exterior work, as it can be used immediately, without requiring time-consuming to prepare the working mixture, and quickly vulcanized with the participation of moisture in the air.
If you need to get rid of cracks or gaps that occurred during the construction of a house or simply appeared in concrete walls with time, or to achieve waterproofing of some objects, then using various types of sealants, you can easily solve this problem.