I have no comment on the concatenation itself, but I'd like to point out that @Jakub Hampl's suggestion:
For building strings in the DOM, in some cases it might be better to iteratively add to the DOM, rather then add a huge string at once.
is wrong, because it's based on a flawed test. That test never actually appends into the DOM.
This fixed test shows that creating the string all at once before rendering it is much, MUCH faster. It's not even a contest.
(Sorry this is a separate answer, but I don't have enough rep to comment on answers yet.)