PU foam, versatile and proven
The first construction foams appeared on building sites in the early 1970s. Today, there are special foams that have been optimised for almost every specific purpose. For instance, there is an assembly foam that is particularly well suited for application in the winter. Here is an overview of the most important PU foams.
Well foam was developed to allow waterproof adhesion of concrete rings and well shafts. It can also be used when setting shaft rings, drain shafts and domestic sewage plants. This special construction foam is resistant to thinned chemicals and is also resistant to rotting (resistant to bacteria in the earth).
Practical tip: Sealing wells and cisterns with well foam
1-component PU foam
1-component PU foam cans have a market share of 80 percent and therefore dominate the construction foam market in Germany. 1-component PU foams only need to come into contact with normal humidity in the air to foam and harden. These assembly foams do not require any further components. It is recommended spraying the connection surface with water before and after applying the foam to accelerate the hardening process and improve the quality. The 1-component assembly foam hardens from the outside (where moisture impacts first) inwards. In 1-component PU foam cans, isocyanate and polyol are mixed in the can during production: this is then referred to as a pre-polymer. A classic application for the 1-component construction foam is insulating windows.
2-component PU foam
The 2-component PU foam is much stronger than 1-component construction foam and hardens very quickly and evenly. This helps to control the hardening process. If the strength, hardening speed and homogeneity of the foam structure are dominating factors, it is best to opt for a 2-component PU foam. A typical use for 2-component assembly foam is the fitting of doors. 2-component PU foams do not react with ambient moisture, instead they have another reaction partner: the so-called wetting or hardening agent. This is located as an extra packaging element, either in the can or supplied separately. Before starting, the user must activate the hardener so that the pre-polymer in the can and the hardener can be mixed well. This process is described on the can. The success of the mixing process is shown by the even colour of the PU foam. 2-component foams, in which the substances in the can react, need to be processed within the time stated on the can label.
Frame foam – the PU foam specialist for interior doors
Doors should absorb day-to-day impacts without wobbling. This is why there is special frame foam that is used to attach door frames allowing them to withstand continuous heavy loads. What properties does this foam need? Frame foam needs to be highly adhesive and strong, and also needs to harden quickly and reliably. Also, it should be dimensionally stable after a very short time and not spread.
PU foam adhesive/perimeter foam
This alternative to cement and mortar adhesives in thermal insulation composite systems offers a clean and fast method with all the benefits of adhesion to different surfaces. If parts are adhered on surfaces suitable for adhesion, mechanical fixation is unnecessary. The main application areas include the installation of thermal insulation composite systems, cellar ceilings or flat roof insulation.
Winter foam is a special type of assembly foam that can be used at low temperatures. Under normal circumstances, construction foam should not be used below 5°C because the humidity required for hardening is lower. Winter foam is therefore the solution for cold weather. PU winter foam can usually be used up to temperatures of -10°C. Manufacturers also supply construction foam that can be used up to -20°C for countries with very cold winters. This does not refer to the temperature of the can; this should always lie above 5 ° Celsius.
B2 construction foam and B3-PU foams
In Germany construction foams of the construction material class B2 are usually sold.
This means that the construction materials have been classified as normally flammable according to the flammability class regulations of DIN 4102-1. They can be used throughout the building apart from in places subject to special fire protection requirements. In rare cases, easily flammable B3-PU foams are sold in retail outlets. These B3-PU foams are not allowed to be used for construction projects.
Fire protection foam and B1-PU foam
Construction foam that has been developed as flame retardant PU foam for filling and sealing joints is commonly referred to as fire prevention foam. It must satisfy the requirements of the standard DIN 4102 (B1) Fire behaviour of building materials and building components or the European standard EN 13501 (Fire protection class B). If there are special fire protection requirements, for instance if fire resistance classes defined in the EN 13501-2 (EI) are to be reached, these special foams are used in conjunction with other fire-retardant materials.
An isocyanate-reduced foam is a foam whose concentration of the reactive MDI (= Methylene diphenyldiisocyanate = free isocyanates) has been reduced. These foams are divided into two groups:
A) < 1% monomer level
The level of free MDIs in these foams has been reduced to a value below 1 %.
B) < 0.1% monomer level
The MDI level in these foams has been reduced to a value of < 0.1 % of free MDIs.
MDI-free foams with a silane base
These are assembly foams that have a polyurethane structure but no more free isocyanate groups because they were turned into a non-reactive urethane structure in a previous chemical process. The foam hardening process is based on reaction-capable silane groups that, once the foam has left the can, react with the ambient moisture leading to the interconnection and therefore the hardening of the applied PU foam.