As I understand your request (with Google Translate) you wish to illustrate ceramic tile joints in your FormIt model.
I would suggest two different approaches depending on the presentation method. Either create a material with the appropriate joint and tile dimensions and paint the surfaces or model the joints as 3d lines on the faces of the floor surface.
Material approach:
1. Download, create or modify an image file of a ceramic tile grid with the correct proportions for each type of ceramic floor;
2. Create a FormIt material and assign the image file. Adjust the material dimensions to get the correct dimensions (i.e. 40x40cm or 25x50cm);
3. Apply the material to the surface and adjust the orientation of the pattern. https://windows.help.formit.autodesk.com/tool-library/materials#adjusting-material-placement
The advantage of the material approach is to get a more realistic view. The disadvantage is having to find a material map that has the correct tile pattern and joint size/color.
Modelling approach:
1. Group your floor surface;
2. Draw your model lines in a new group (so that they don't cut your floor surface);
The advantage to the modelling approach is when you export to a CAD or Revit model, you can snap to the geometry.
Hope this helps,
-luc
