Fix a windowsill


To fasten a sill, different techniques and materials can be used. Below is an overview of when you should use which method and which material to fasten a sill.

Distinctions between inner and outer windowsill

First of all, you have to distinguish between the inner and the outer windowsill. The latter is also called Sohlbank. However, mounting the outer sill requires a great deal of expertise, especially in a new house with thermal windows and composite thermal insulation system. The sill must be mounted absolutely airtight. The following materials are suitable for window sills:

  • Wood (inside)
  • Artificial stone (inside, outside)
  • Natural stone (usually inside)
  • Metal (outside)
  • Plastic (inside, outside)

Used adhesive for fixing a windowsill

In principle, any, including the metal window sill, can be glued. For this purpose, either mortar, assembly adhesive or mounting foam is used. However, mounting foam and assembly adhesive are preferably used inside, mortar on the outside. In addition, mounting adhesive is preferably used instead of mounting foam. Too much mounting foam can lead to uncontrolled lifting of the sill plate.

Attach a sill made of heavy natural stone

For natural stone slabs as a window sill, it is also advisable to provide the bottom of the plate, such as a granite slab, in advance with granite adhesive. Then the granite windowsill is simply placed in the previously prepared mortar bed and aligned. If such a window sill, especially outside, does not have enough contact surface, knock some plaster off the facade window underneath. Here you can now attach a metal angle profile and plaster it again later.

Fix wooden or metal windowsill

Even some metal windowsills are dowelled on the sides with screws to the soffit. However, this is no longer a common method in modern homes whose windows must be absolutely airtight. Instead, these window sills are placed in a glue bed. Inside the wooden window sill, you can use different adhesives. Even with acrylic, you can stick a wooden window sill.

Note special features when installing

Note that the outer window sill must have a five-centimeter drop to allow the water to drain. In addition, the sill has to survive a bit, so that the running water can not reach the facade. The inner window sill is planned 1 to 3 cm wider and then inserted through a groove in the soffit. Also on the front of the window sill should survive something. For more information, see Building windowsill.

Tips & Tricks

After you have fastened the windowsill, it still needs to be sealed. How to proceed when sealing a window sill is explained here.


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