Table in Writer with column dividers of different line thicknesses, how?

I have created a table in the default table style with 12 columns and 100 rows. The borders and column dividers are all 0.5 pt (1 pixel on my monitor). I’d like to make every 4th column divider 1.5 pt. Using Table properties/Border my only choice seems to be to make all the column dividers 1.5 pt. The table preview shows, under User-defined, a table with only 2 columns.

Restyle first your table as None. Any other “table style”, such as Default Table Style will play dirty formatting tricks on your back whenever you change something in the table. Those so-called styles always override your formatting adjustments. They are intended for people accepting the “styles” as is, without any possibility to make persistent modifications.

Once you have done this, follow this procedure:

  1. Select every 4th column and right-click for Table Properties.
  2. Go to the Borders tab.
  3. Click on the left border to select it
  4. Adjust the Line properties (style, colour, width)

PS: when asking here, always mention OS name, LO version and save format.