Multi-functional sealing strips and mechanical mounting

The question of mechanical mounting on structures always comes up when sealing using multi-functional sealing tapes made from impregnated PU foam. When used in conjunction with fixings, spray foams are said to have supportive effects in that they also bond the window frame to the building structure and provide a secure hold. Is this really the case? What is the purpose of the screws and how long does this “adhesive” last?

Page 93 onwards of the Installation Guide from the RAL Quality Associations deals with the topic of fixings and gives detailed answers. The following are given as the fundamental principles for fixing:

“Normally a circumferential, mechanical fixing with suitable fixings must be provided for windows / external doors in punctuated façades. A definitive fixing is not possible with the current state-of-the-art in-situ foams (PU spray foam), adhesives or similar construction materials. The fixing must take place by mechanical means.”

Various screw systems are available to use for mechanical fixing in conjunction with multi-functional sealing tapes like ISO-BLOCO ONE for sealing.

Dry wall screws have a cutting thread profile and are available in 7.4 mm and 11.4 mm thicknesses  for drill holes of 6 mm or 10 mm.

This means that the construction component is fixed using a classic push-through installation. It is important to note that these screws can be used for solid wall-building materials. If the wall-building materials become brittle or are made of hollow bricks then it is recommended that the screws are used in combination with 90 mm long plastic wall plugs. The plastic wall plugs usually bridge more than 3 chamber walls and therefore provide enough hold. Normally additional packing is not necessary.

It is also possible to use straps / metal tabs as long as these are bent at a right angle on the inside, external from the joint and in front of the multi-functional strip. Adjustment anchors and carrying plates can take over the supporting load-transferring and vital functional tasks. These are installed centrally using the multi-functional sealing strips and therefore do not disturb any sealing layers.

Even if practitioners like to talk about how using PU foam adds extra grip, this is not a permissible method of fixing as it has no long-term effects. On this note, it is worth remembering that liability is considerably reduced over time and can lead to high compensation costs for the installer in cases of accidents. Even though it rarely gets that far, the user will notice a reduction in quality which is marked by sticking windows. This is because over time they have become loose and are no longer securely fixed into the wall.