What Is Polyurethane Waterproofing Coating?
Polyurethane waterproofing coating is a material applied to balconies, the common facilities of condominiums, and other places where waterproofing is required.
Polyurethane waterproofing coating is often used because it is relatively inexpensive, easy to work with, and can be applied to many surfaces.
Uses of Polyurethane Waterproofing
Polyurethane waterproofing coating is used in many structural elements, including rooftops, balconies, open corridors in apartment buildings, and stairways. Polyurethane waterproofing coating used to waterproof these spaces can be broadly divided into two types: one-component sealants and two-component sealants, the latter being used after mixing with a hardener.
1. Single-Component Polyurethane Waterproofing Coating
Single-component polyurethane waterproofing coating is used to waterproof balconies and similar spaces because it is very easy to work with.
2. Two-Component Polyurethane Waterproofing Coating
There are two types of two-component polyurethane waterproofing coatings: manually-applied and sprayed. With manually-applied coatings, the base compound and curing agent are mixed and applied, then cured at the temperature of the surrounding environment. This type of coating has a rubbery, elastic surface and is commonly used for waterproofing rooftops and balconies.
The manufacturing of spray-type polyurethane waterproofing coatings started with the development of rigid polyurethane. It is applied by spraying the polyurethane and a curing agent while mixing them in a specialized machine. Since it begins to cure in less than a minute after application, it is commonly used in sloped areas and heavily-trafficked corridors and stairways.
Rigid polyurethane waterproofing coating is also used in civil engineering applications, such as bridges, thermal storage layers, and underground waterproofing. The use of polyurethane waterproofing can protect structures from water, protect concrete from salt damage and neutralization caused by carbon dioxide gas, and prevent concrete spalling. It is also used on roads to prevent deterioration caused by expansion and contraction due to vehicle traffic and snow-melting chemicals.
The spraying method also makes it possible to apply coating even in places that may not be sufficiently dry, such as uneven surfaces and underground. Furthermore, rigid polyurethane waterproofing coating has excellent chemical resistance, heat resistance, crack tracking, and abrasion resistance, and is used for coating sewage-related facilities, offshore structures, steel tanks, structures, etc.
Principle of Polyurethane Waterproofing Coating
Polyurethane waterproofing coating is a generic term for polyurethane resin or polymer. Polyurethane has exceptional properties for pressure resistance, waterproofing, and elasticity.
1. Single-Component Polyurethane Waterproofing Coating
Single-component polyurethane waterproofing forms a waterproof film via a polymerization reaction between isocyanate (the base compound) and polyol (the curing agent). When single-component polyurethane waterproofing is applied, the isocyanate group-containing base reacts with moisture in the air to cure at the ambient temperature, so it takes about 24 hours to cure.
2. Two-Component Polyurethane Waterproofing Coating
Two-component coatings can be further classified into two types: manually-applied and sprayed.
Manually-Applied Coatings
Manually applied coatings require the mixing of a polyisocyanate-based base compound and polyol-based curing agent before application. The base compound is a viscous liquid containing isocyanate groups at the molecular ends of the polyurethane prepolymer. The curing agent is a paste-like material containing amines, polyols, fillers, plasticizers, and stabilizers, which react with the isocyanate groups of the base compound.
When working with manually-applied two-component polyurethane waterproofing material, a pressure pump is used to dispense the material, eliminating the need for mixing equipment. The advantages of this system include improved work efficiency, less unloading work, and significant waste reduction. The mixing is done automatically, supplying a uniformly-blended coating with no risk of mixing defects.
Spray-on Coatings
Spray-on two-component polyurethane waterproofing coatings using rigid polyurethane also utilize isocyanate and polyol to form a waterproofing film. Spray-on coatings are characterized by the fact that the base compound and curing agent are each pumped under high pressure, mixed in the spray gun, and sprayed on.
The advantage of this type is that it hardens quickly, so the same material can be used for both flat and vertical surfaces. However, since spraying machines vary between manufacturers, it is essential to seek guidance from the waterproofing material manufacturer before installation.
Other Information on Polyurethane Waterproofing
1. Polyurethane Waterproofing Coating Application Methods
Single-component and manually-applied two-component polyurethane waterproofing coatings are all made by solidifying the liquid material to form a waterproofing membrane. The advantage of this process is that it’s relatively simple. In practice, a priming layer, which enhances adhesion, is applied to the surface before waterproofing, and the polyurethane coating is then applied on top of the primer.
However, when applied to some surfaces, such as concrete, there is a disadvantage in that cracks in the concrete are transferred to the coating, which could potentially lead to rupture. Another disadvantage is that water vapor retained in the substrate of the surface could cause swelling and other issues.
As a result, a construction method combining ventilation buffer sheets and polyurethane was developed. In this approach, a primer is applied on top of the substrate, covered with a ventilation buffer sheet, and the polyurethane waterproofing coating is applied and cured on top. With the sheet placed between the waterproofing material and the substrate, it is possible to prevent ruptures and swelling due to moisture in the substrate. Since the adoption of this method, polyurethane waterproofing, which used to be used primarily for small-scale renovations, has become viable for use in new construction and large-scale waterproofing ventures.
2. Topcoat Used for Polyurethane Waterproofing
Just as in painting, a topcoat is a material applied as a finishing layer after the application of a polyurethane waterproofing coating.
One of the drawbacks of polyurethane waterproofing is the tendency of the coating to discolor when exposed to ultraviolet light. Also, because of how they cure, there is a risk of cracking and deterioration. A topcoat helps protect the waterproof coating from ultraviolet rays and prevent the above-mentioned deterioration.
Additionally, since polyurethane waterproofing coatings have adhesive properties, dust and dirt can easily adhere to the surface if left untreated. This can build up and be difficult to remove, so a topcoat also serves to mitigate the adhesion of dirt.
Topcoats both address the weakness of polyurethane waterproofing coatings and mitigate their deterioration. Therefore, applying a topcoat is a critical finishing step in the overall application process.
3. Calculating Quantities for Polyurethane Waterproofing Coating Application
The application quantity refers to how much material is needed to optimize the performance of the polyurethane waterproofing coating.
If the specified application quantity is 0.7 kg, for example, 7 kg will be needed to cover a 10 m2 installation area. But in practice, the surface may be uneven, affecting the exact measurements of its area and its shape. Failing to consider this could result in a significant miscalculation of how much material is needed. As such, considering the shape and surface irregularities when calculating application quantity is crucial.