34grid : How to create a column with 2/3 width?

34grid : How to create a column with 2/3 width?

Using 34 Responsive Grid system, how to create a column with two-third of
full width ?
The Grid System has equal columns settings, but how can I colspan / merge
2 columns ?
<div class="container">
<section class="row">
<div class="col_1">100%</div>
</section>
<section class="row">
<div class="col_2">50%</div>
<div class="col_2">50%</div>
</section>
<section class="row">
<div class="col_3">33%</div>
<div class="col_3">33%</div>
<div class="col_3">33%</div>
</section>
</div>