Redirect part of a website to https and http

Hello,

I need to have all my website on https except one directory that I must have on http (because of a plugin that is not SSL friendly).

I implemented the following .htaccess file:

RewriteEngine On

RewriteCond %{HTTPS} on
RewriteCond %{REQUEST_URI} ^/blog/
RewriteRule ^(.*)$ http://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

RewriteCond %{HTTPS} off
RewriteCond %{REQUEST_URI} !^/blog
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^logout(.+) wp-content/themes/mc/logout.php$1 [R,L]
</IfModule>

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

Somehow this doesn’t work as expected. When I try to access the website example.com/blog/ I get a redirect loop.
What am I doing wrong?

Cheers
Luca