What are the advantages of a foam adhesive over the traditional anchor fixing of thermal insulation boards?
The obvious answer is that installation gets much simpler: no rotary hammer, no drilling into the wall. But that is only one advantage out of many. To see what else you gain by using a foam adhesive instead of anchors, let us first look at what goes on inside a wall when a facade is insulated with these materials.
Thermal insulation boards do more than save energy and add comfort: they also protect the structure from the effects of temperature swings. Insulation moves the greater part of the thermal gradient out of the wall structure and into the insulation board. But together with the gradient, the load from thermal movement moves from the wall into the board as well.
This is how heat travels through a double-leaf masonry wall. The black curve is the temperature profile without insulation, the red one is with an 80 mm layer of insulation. Left: winter, -5°C outside, +20°C indoors. Right: summer, +30°C outside, +22°C indoors.
A temperature difference of that size causes thermal movement of the insulation boards, in winter as well as in summer.
This movement is the main source of the loads that act on the systems holding the boards to the wall, whether these are mechanical anchors or a foam adhesive.
With mechanical fixing — usually five anchors per board — the entire load is concentrated at those five points and can exceed what the board material will take. The board may then be damaged. Five anchors also cannot hold a board completely still: under changing temperatures it still works, and that loosens the layer of plaster applied over it.
Unlike anchors, a foam adhesive is spread over a large part of the board area and distributes the movement load far more evenly, with no stress concentration at individual points. The larger contact area also holds the board much more securely, so it does not work under temperature changes and the plaster finish over it survives far better. On top of that, no anchors means no thermal bridges. And where boards do not fit tightly against each other, the same foam adhesive fills the gaps between them, giving a continuous layer of insulation.
