Postfix? The only Postfix I know of is that ready-mixed rapid-hardening concrete mix available in the UK which you pour dry round your fence posts and then pour water over it. It sets in about 30-60 minutes.
Ready-Crete is the brand name in the states, as I recall...used for the same purpose
Yes, I think I may have seen that in the UK, but there are a number of different brands.