What should I use to fix the windowsill? What type of mortar should we take?

At the beginning of October, the granite windowsills for our home will be delivered; we want to install them ourselves. The wall is made of 36.5 T12 stones. Can I set the windowsills with normal cement mortar, or should I better use LM21 (light masonry mortar)? What is best to use there?

When installing your interior windowsills (I assume these are interior windowsills), you must also ensure that they do not touch the exterior windowsills below the frame (thermal bridge). The cavities of the Poroton bricks are filled with mortar, then mortar is applied at the appropriate height and smoothed off. Before installation, light granite varieties are additionally sealed on the underside with white natural stone adhesive and then set with flexible tile adhesive.

I did it myself back then as well. For the outside, I used regular cement mortar. Before that, I applied the granite adhesive under the windowsill with a trowel. It is also important to seal well here.

Hello,

Just like the member Herrmann, I did the same. This is the easiest way and it still holds up well today.

Best regards

Thank you for the tip, because I have to do that at my parents' house next week. So I am informed and can get the materials.

I also used masonry mortar for the interior window sills. It is also important that there is enough air to the exterior window sill. Be sure to avoid thermal bridges here.