I just want to let you know I have figured it out. New day, fresh head it seems.
I would make a video but it would be too big for this platform.
To make a chamfered tiled skirting you need to first apply material and than chamfer:
Create a rectangle, extrude, group. Go into edit and paste in the object from which you would be sampling the texture using ThruPaint.
-In Material section select Sample Material from Faces of the Model.
-In UV Mapping select Projected UV.
-In Selection select Surface. Make sure your Axes are set to the corner of your model.
-In Surface’s submenu go to Local. Select every one of three plane options one by one by applying texture to each plane separately, e.g…: select horizontal plane in the menu and hoover over horizontal face the with the mouse until plane shows up, click and apply material. Do the same with two other planes.
To position texture so that the grout is in line on top and front faces you need to test by clicking one surface more to the left or right of the face, that switches direction of the texture.