I use it sparely. I oversize my block normally (when possible) so I use it when I am pressing my blocks before trimming. I don't think it gunk up my Rowenta tho I do clean it about twice a year. I have never had a problem with "Magic Sizing" that use to be in only available at the super Walmart. But I grabbed some cans when I was last in my local small Walmart. It is in a bright blue can.