I need to paint the concrete window sills and the window surrounds on my roughcast kit bungalow near the Atlantic coast of the Isle of Lewis in Scotland. They're painted at the moment but haven't been maintained for some years. The sills I think have been done with some kind of matt external paint and are crumbling but only very slightly and on the surface and not sufficiently to require skimming. The surrounds have been done with something more glossy.
The guy in the paintshop recommended a 3:1 water:PVA coat after scraping, and then some Dulux Weathershield. He didn't seem to know much about SBR or alternatives to that brand and type of paint.
Should I use PVA or SBR or something else? I thought for a while that maybe he's right at least on the PVA score because a decent paint will soak into the concrete which SBR being waterproof would hinder. I'd be grateful for advice from some of the knowledgeable people here.
And what should I do about the surrounds?
Third question... The walls are roughcast and look mostly okay for the time being although in places they are weather-stained and I plan to paint them. I was thinking one coat of SBR followed by two coats of masonry paint. Does that sound okay? Or would it amount to putting a vapour barrier on the cold side of insulation and thereby muck up the ventilation something rotten? I'd like to use paint that doesn't need to be recoated in the next 20-30 years.
Thanks in advance,