Based off the original UI Blocker for Meteor, I created a fork to use the Semantic UI loader, which you can find here:
https://atmospherejs.com/tripflex/suiblocker
Enjoy 
That’s cool , Is it accessible ? If not it would be nice to make an accessible one, and a paper style. See Papercss.
Well thanks for sharing !
What’s your use case for an UI blocker?
Are you using it while doing some async task in the browser? e.g. fetching something using the fetch API and a promise?
The only use of an UI blocker I have seen so far is with a piratebay proxy for example, you get an UI blocker while a DDoS checker runs for a few seconds…