Installing natural stone window sills indoors.

Hello,

I want to install the natural stone window sills myself inside our house.

At the building materials store, they recommended Trass cement mortar for the installation.

... So far, so good ....

What do I need to pay attention to during installation?

Is the mortar applied with a notched trowel (like with tiles)?

Or, I would decide this instinctively, place the stone slabs in a "mortar bed" and then level them with a spirit level.

Do I need to treat the slabs or substrate beforehand? Primer, etc.?

The window sills will be fastened to calcium silicate stone and the plaster on top of it.

Back then I also laid granite in trass cement mortar...

Horizontal formwork board with plaster anchors fixed on the front side so that it marks the future height of the windowsill, paying attention to any desired slope. Since condensation water can occur on the windows and pouring water on the sill, a slight slope could possibly be useful. Normally, the amount of water should be so low that in my opinion a slope on the inside could also be dispensed with. This way "the lady" can later nicely fill everything with flower pots without them standing unevenly

The KS bricks absorb very strongly and in my opinion must be well pre-wetted (no puddles!). As long as the bricks are still dark from moisture, I applied the trass mortar with the trowel, spread it evenly and then leveled it along the formwork board (aluminum strip with integrated spirit level), precisely maintaining the level or any desired slope relative to the window when leveling. I laid the well pre-wetted windowsill into the carefully leveled mortar bed. I slightly pushed it back and forth to achieve full-surface support. Nothing is worse than a hollow-laying natural stone windowsill. Once supported or a huge flower pot from the wife and: crack!

In my opinion, the sill should definitely not touch the window frame, so I left a 3-5 mm gap. The joint was later sealed with silicone suitable for natural stone. Granite also expands, plastic even more so, so in my opinion a tight fit could lead to problems.

The interior windowsills can each be recessed 2 cm into the reveals. This can be achieved by a corresponding projection of the reveal plaster, without having to chase out. In my opinion expansion joints should again be formed here, possibly by inserting styrofoam strips.

I am not a professional, that’s how I did it, no problems to date (installation 8 years ago).

Regards

Thank you for the response.

The idea with the Schalbrett is good.

Did you remove the board before inserting the bench? Otherwise, the bench rests on the board and cannot "sink" into the mortar bed.

Hi,
Trass cement is already good.
Personally, I skip the shuttering board, spread the mixture on the surface, slide the windowsill under the window frame, and make sure it doesn’t hit the back. With the small spirit level, I then bring it into a horizontal position.
To avoid solid connection (cold bridge), I press two small wedges under the frame at the back. This creates a counter slope, which people argue about.
If you make a slope forward or install the windowsill level, you always have the optical illusion that the sill is about to slip out.
I prefer a slight counter slope and wipe away the condensation water with a cloth rather than have it running into the room.

Regards Dirk

OK,

then many thanks for the useful answers.

Next Wednesday I will install the window sills and then report here in the evening with this and other pictures.

Have a nice rest of Sunday.

Regards

Yeah cool,

accomplished something again. Interesting site; I need to take a closer look at it sometime.

Continued success!

Regards