exclude category in Mixfolio template

Hello,

i wanted to exclude one category from the dislayed posts in the Mixfolio template.

I guess I already find the right part of the code (main index template) but the way I entered the exclude code doesn’t work:

THE CODE:

<?php
					$paged = ( get_query_var( 'paged' ) ) ? get_query_var( 'paged' ) : 1;

					$grid_args = array(
						'posts_per_page' => get_option( 'posts_per_page' ),
						'paged' => $paged,
					);

					$grid_query = new WP_Query( $grid_args );

					while ( $grid_query->have_posts() ) : $grid_query->the_post();
				?>

I entered “cat=-1” in this code area

get_option( 'posts_per_page' ), 'cat=-1',
						'paged' => $paged,

How do I have to write it?
The code doesn’t look exactly like in the wordpress documentation.