To charge? (and how much?)

[LoopyLoopyLoopy]

A friend of DH's colleague (someone I don't know) asked around for some help with his masters - he isn't English and needed proof-reading. I am pretty good at that, so agreed, as a favour. He offered money, but I said no, totally underestimating how much work it would be.

He is now sending me about 3 documents every 2-3 weeks to correct (which does take some time, as I am a teacher by trade and like to explain why he is wrong, rather than make the correctios for him).

Would I be unreasonable to go back to him and say, sorry, I didn't realise how much work this would be, and suggest rethinking payment? And if so, how much?

YANBU.
Check out the rates on www.peopleperhour.com and get a feel from that.

Absolutely.
Exactly as you've said here.
If it's a 'favour' then probably £5 per hour.
But if you want to be paid properly then then £10 per hour.

Love that I made a typo in a thread about proof reading!

Anyhow, I sent the email and he got back to me straight away with a figure of 10pounds per document - some are short and some long, but none so far have taken me an hour.

Does this sound OK? Sounds fab to me!

Yes, as long as you specify to him that all the materials he sends you will be of a similar length. Perhaps give him a total number of pages or words that he shouldn't exceed. You won't lay yourself open to any other micky-taking then.