Good to know

Side weld sealing

Side welds along the perimeter of the contiguity of the window to the opaque parts of outside walls during the operation process are subject to force loads and different impacts of both internal and external environment. When sealing side welds always take into account that humidity in the room should not condense at the appropriate decrease of temperature. In case when external weld’s part is sufficiently ventilated, the condensate emerges, however if during the period of drying the cold bridges form, the wet environment have a destructive effect on the construction.


In case when internal weld’s part is made properly, moisture can get into it only from external weld’s part. As external temperature and temperature of external weld are equal (happens only in case when sealing in functional area doesn’t transmit the heat into the external weld) sweating nevertheless is possible, weld is “breathing”, draining from moisture. The easiest way to ensure weld’s „breathing” – use of pre-compressed sealing strip which doesn’t pass the water, but passes air.


When using sealing mastic it is necessary to leave open places where the probability of ingress of water is minimal. Thus is provided the transmission of air to the outside. When sealing side welds follow the common rule: „from inside more airtight than from outside”.  Consequently the weld shouldn’t pass even air moisture; in functional area proper sealing should be done and external weld „has” to breathe, but do not pass the moisture inside.

Below are the sealing options for joint between the wall and window frame.
Joint sealing of the wall and quarter

Window opening with a quarter are found most frequently in renovated and new buildings. When installing the windows in such opening welds can be easily sealed as wind and rain has a direct impact only on the outer perimeter of the window, the weld’s width in tis case veries from 5-10 mm. Also the sealing of such weld is simplified by the use of polyurethane foam, as there is no possibility of foam getting on the facade surface and its damage. The surface of the exterior panels doesn’t protect sealing of the weld from wind and rain, as surface of the windows do not fit close to the opening (and PVC profiles of the windows shrinking and expanding under temperature fluctuations) – thus, in case of the opening with a quater the sealing of external welds with mastic or expanding layer is needed.

Joint sealing for the wall without quarter

Construction of the walls without a quarter is represented in many panel and frame-and-panel houses where the outside side welds were sealed with decorative cover strips. When sealing such welds take into account that installed outside cover strips don’t protect from UV rays, either from atmospheric moisture that is why it is recommended to use additional sealing.

The following additional sealing is used:
  • pre-compressed sealing strip for outside sealing;
  • outside cover strip joint sealing to the wall construction and window with the silicone sealant;

Be careful when sealing weld with polyurethane foam sealant in the functional area as sealant under pressure may get accidentally on the façade surface. When working in old wooden buildings the most wall construction is construction without a quater that is similar to the construction of stone buildings.

When sealing the joint with pre-compressed strip it is necessary that its width is a half narrower than the width of the joint. When additional sealing is carried out using mastic then in places less likely for ingress of water is necessary to leave small gaps in mastic weld inside the joint.

NB! When filling the joint with polyurethane foam insulation in the functional area make sure that sealing is without gaps along the whole perimeter of the window including bearing and thrust elements of the window.

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