There is an (100 yer old) internal cast iron soil pipe from upstairs runs vertically through our utility room. It has been painted over the years with a few coats of emulsion. We're redecorating so I stripped off the old paint and cleaned it up.
When cleaning it up, I noticed a few small (10mm max) blisters on the old paintwork with pockets of damp/rust behind them. Regardless, I gave it a couple of coats of metal primer with intending to paint it with the same emulsion as the walls when I get that done (this weekend).
However, after a week, there are tiny bead of rust/water has come through the undercoat. There's not enough to form a drip, just a small brown patch coming through the paint. It's not a big problem, and I certainly don't think it worth replacing the pipe - more of a cosmetic issue really.
Can anyone suggest a teatment that would keep it blemish free. What I don't want to do is put the emulsion on and have the brown spots come through that too.
Thanks.