Borders on multiple cells selection in Calc

Hi all. I really would like to put an external thick border on a group of multiple cells, but when I select the cell group and the border specification, this specification is applied on the border of the single cells INSIDE the selection, when i need to thick the OUTSIDE border. I hope I was enough clear: in Excel, you just need to click on the square command on the BORDER button to obtain this… Thanks in advance for any suggestion.

Menu: Format>Cells

Thanks for the suggestion: I already tried it, the problem is that with this method yhe borders of the INSIDE cells are cancelled…