I plan to paint the inside of a porch, which is currently bare brick. It’s enclosed, so sheltered from the weather, but not heated. Would a coat or two of diluted PFA then two or three coats of emulsion paint work ok? Emulsion because I understand it’s porous.

Ac oat of watered down PVA (not sure about PFA) then Vinyl based emulsion should work very well. If you don’t use PVA first the bricks soak up a lot of paint. We used to paint the lines on the track at Halesowen cycling club with mat vinyl emulsion and they lasted years, outside in all weathers.

Thanks, and you’re right, it’s PVA.