The protection of health, safety and environment while reducing risks and resource consumption is of growing significance for regulatory agencies as well as all other parties involved in the planning, construction and refurbishment of buildings and civil engineering structures. For the construction business, waterbased pretreatments provide user-friendly products in combination with economic advantages and excellent technical performance in terms of adhesion, long-term durability and reliability.

Durable bonds with waterbased primers

The use of waterbased pretreatments for bonding applications is rapidly increasing in the construction of buildings and civil engineering structures. The reasons are the excellent adhesion promoter properties on a wide range of substrates. In addition, these primers provide the basis for long-term durable bonds in combination with PUR- and PUR-hybrid adhesives.

Best practice to achieve high quality bonds in terms of adhesion and durability usually implies the use of a suitable surface pretreatment. Typically, 1- or 2-component primers are applied on the clean surface, where they cure to form a tough and thin film layer. They provide the adhesion-friendly surface needed for bonding with polyurethane (PUR), PUR/hybrid or silicone adhesives and sealants.

For typical construction materials such as concrete, natural stone or wood, epoxy or isocyanate based primers are most commonly used. To date, those primers often contain organic solvents for improved application properties. This stands in stark contrast to adhesives and sealants, where solvent free systems have been state of the art for some time. In order to meet the increasingly demanding regulatory requirements and customer requests, the development of solvent free pretreatment systems became a focus. As a result, waterbased epoxy primers for woodfloor bonding and joint sealing on construction sites are now available.

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Envoronmentally Friendly

Conventional primers contain volatile organic solvents that tend to be harmful for the user and the environment. In contrast, the waterbased primers that are subject of this publication, are completely solvent free and “very low emission” as classified by Emicode. Because the products are neither dangerous goods for shipment nor corrosive (see Table 1), they are available in environmentally friendly packaging such as plastic containers and foil pouches.

Table 1: Comparison of product properties of commercially available waterbased and conventional 2C epoxy primers

High Performance and waterbased

The most important function of a primer is to promote adhesion between the sealant/ adhesive and the substrate. The adhesion promoting properties of the waterbased primers in combination with PUR, PUR/hybrid- or silicone adhesives and sealants was tested according to DIN 54457 on a wide variety of substrates typically used on construction sites. In order to validate the durability of the bonds, the test specimens were evaluated after various ageing cycles. The adhesion and durability performance of waterbased primers was found to be equivalent to the performance of the conventional reference products. Additionally, for woodfloor bonding, the primer serves both, as adhesion promoter as well as barrier against humidity migration from the cement screed subfloor.  

Userfriendly

Conventional 2C epoxy primers often suffer from a very strong, pungent odor. The waterbased systems on the other hand are nearly odorless. The mixing of the two primer components is very simple. Component A and B are both low-viscous liquids that are readily mixed in the packaging by shaking. There is no need for a separate container or special mixer, as it is generally required for conventional 2C epoxy primer. After mixing of the two components, the cross-linking reaction immediately starts. Whereas this reaction is highly exothermic in case of conventional 2C epoxy primers, the heat generation for waterbased primers is minimal. The latter are in addition non-flammable (Table 1).

Waterbased primers can immediately be applied after mixing. Thus, there is no delay due to induction times. The waterbased systems offer a very attractive pot-life of 2-4 hours that allow for enough time for the  user to complete the application after mixing.In order to achieve a durable bond, it is absolutely mandatory to allow the 2C primers to cure before further application. The curing time of the primer is strongly dependent on temperature and humidity. For waterbased primers, curing is achieved within 4h at standard climate (Table 1), whereas 2C conventional products require at least twice the amount of curing time at the same climatic conditions. With the waterbased products, sealants or adhesives can thus be applied the same day instead of waiting for the following day. In order to reduce moisture migration, for example in basements, a second primer layer can be applied once the first one is cured. During curing, the waterbased primer undergoes a color change from white to transparent. This provides the user with an easy and reliable indicator that the
pretreated substrate is ready for the next working step.

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Application 1

The primer is poured directly onto the substrate after mixing.

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Application 2

The material is uniformely spread on the surface with a brush or roller. The primer forms a white film on the surface.

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Application 3

At standard climate, the primerfilm becomes transparent after approx. 4hours. This indicates that the surface is ready for bonding.

Economical

Finally, the waterbased primers are attractive from an economic standpoint as well. In order to achieve the same properties regarding adhesion, subfloor consolidation and moisture barrier, the consumption of the waterbased primer is less than half per square meter than for conventional reference products (Table 1). Depending on the size of the area to be treated, the application is done using either commercially available brushes or rollers.

The tools are cleaned with water and are reusable. No cumbersome cleaning with solvents is necessary, which results in a combined advantage regarding cost-saving and less environmental pollution. Because the primers are not classified as dangerous goods, the storage and transportation is much more cost efficient and simple. The use of special and lockable solvent cabinets becomes unnecessary.  

The authors

Alain Zahn, Ph.D. is department manager for 1C PUR sealants and adhesives at Sika Technology AG in Zuerich (Switzerland). Judith Grimm, Ph.D. is a senior project leader for the development of polyurethane adhesives at Sika Corporation in Lyndhurst, NJ (United States).

Supplementary Information

GEV – the Association for the Control of Emissions in Products for Flooring Installation, Adhesives and Building Materials – was founded in 1997. Through the EMICODE® it offers consumers, planners, architects and professional craftsmen guidance for the selection of flooring installation products, adhesives and building materials. It provides independent assessments designed to assure the highest level of consumer and environmental protection.

Besides adhesives and levelling compounds, other product categories such as sealants, underlays, adhesive tapes and waterbased parquet coatings are also tested to determine whether they release volatile organic compounds (emissions) to the indoor air which could lead to odors. Members of GEV keep pace with technological advances, so as to formulate and manufacture their products for even greater environmental and health compatibility. GEV monitors compliance with its stringent requirements and conducts regular checks. Products that are labelled with the GEV-certificate EMICODE EC 1 are “very low emission” and offer the best possible safeguard regarding air pollution and odor.