I have been successfully icing sugar cookies for a few months but noticed today that my RI has dried with a sort of 'rough' finish, like hundreds of tiny air bubbles have burst on the surface, it kind of looks like concrete. Any clues why it has done this?

Were the cookies disturbed during drying time? The only time I can recall that mine didn't dry smooth was because of being disturbed.

Thank you very much for the replies. I think it is because they were foamy, they definately have a foamy look about them. I am making the icing correctly though aren't I? Egg whites (safer in my country) and icing sugar beaten for 5 minutes in a mixer?

I use meringue powder and the instructions say to beat for 5 minutes. That's how i got that tacky foamy mess you are referring to. Now i just mix all the ingredients until they are just combined and have not had that problem at all.

Thanks for that. I do remember seeing somebody make it on tv and they only had the mixer on quite slow, I have been beating mine on quite fast. I will try slower next time. Mine looks like meringue, is it supposed to be that thick and fluffy or is that because I am over beating do you think?

I've never used egg whites so I can't help there.

I use meringue powder and beat with the paddle attachment on low for 10 minutes. It's fluffy and stiff enough for me to pipe flowers -- needs thinning for flooding. At 5 minutes, it hasn't come together for me.