Exluding category from home.php – codex solution not working

Hello.

Firstly, I’m sorry if this isn’t in the correct forum, but I was not allowed to post in the ‘advanced’ forum.

On my site : https://www.berryconcept.co.uk/sandbox, I have a case-studies page which displays posts that are in the case-studies category. I do not want these posts displaying on any other page. In fact, I don’t want people to know they are posts at all, it is just an easy way to add case-studies. I have a template solely for the case-studies category.

Here is my case studies page:
https://www.berryconcept.co.uk/sandbox/category/case/

On my home page (splash.php), I have a recent news section, and I have been successful in excluding the case studies category. The loop code on this page is:

<?php global $query_string; // required
$posts = query_posts($query_string.'&posts_per_page=3'); // shows only three posts ?>
<?php query_posts($query_string . '&cat=-19'); //excludes testimonials ?>

<?php if ( have_posts() ) : ?>

<?php /* Start the Loop */ ?>

<?php while ( have_posts() ) : the_post(); ?>

<?php get_template_part( 'content', get_post_format() ); ?>   ...

I have then done the same for my news page (home.php) but this has not worked.

<?php if ( is_home() ) {
query_posts($query_string . '&cat=-19');
}
 //excludes case studies from home page only  ?>

<?php if ( have_posts() ) : ?>

<?php /* Start the Loop */ ?>

<?php while ( have_posts() ) : the_post(); ?>

<?php get_template_part( 'content', get_post_format() ); ?>

<?php endwhile; ?> ...

Any help would really be appreciated.

Also, is there any way of excluding a category from the category section on a widgetised sidebar without editing the wordpress files?

Thanks again.