Masonry paint and filler

[Merlin5]

I painted my front wall a few weeks ago, (http://i.imgur.com/bcUcvg9.jpg) with some Wickes masonry paint that my neighbour lent me. After two coats it still needed a third, maybe a fourth. Anyway, now I want to paint my rear stone window sills (see photos). They were new replacement sills installed and painted end of last year just prior to the new windows being installed, but I think they need freshening up. Am I better off staying away from shops own brands and buying better quality like Dulux Weathershield instead? Would it mean less coats needed, longer lasting, less likely to crack and flake? I can get a 2.5 litre can of Weathershield in brilliant white for £17.98 at B&Q. There's also the other big name, Sandtex. Which out of Dulux and Sandtex is better or are they as good as each other? Will either of these paints last a few years without going off if I keep the tin in the shed? The Dulux has a plastic lid.

I also need to fill the hairline crack in one of the sills. I've got some Tetrion all purpose interior and exterior filler which you mix up. Will that be good? Or, is this better.. http://www.diy.com/nav/decor/paint-...dy-Mixed-Masonry-Filler-9597083?skuId=9957788


Finally, before painting, I guess I should really key the surface. I've got a small roll of sandpaper in the shed, no idea what grade it is, but shall I just use that andgive the sills a quick rub down before painting, will that be sufficient?

 

[Nightglow]

Sandtex ,Dulux, or another brand, it doesn't matter which you used, it the lack of preparation which is the main cause of paint coming away.

I would completely strip those cills & treat with some exterior stabilising primer, this will seal & penetrate the concrete, stop it being so porous & give the paint a good surface to adhere to.

I have used Sandtex Masonry paint, & Dulux Weathershield smooth masonry paint over the years, both lasted well.

Last place had rendered panels under windows, these where primed & painted with Sandtex, 10 years later, paint is still there, hasn't peeled & still looks good.

 

[Merlin5]

Sandtex ,Dulux, or another brand, it doesn't matter which you used, it the lack of preparation which is the main cause of paint coming away.

I would completely strip those cills & treat with some exterior stabilising primer, this will seal & penetrate the concrete, stop it being so porous & give the paint a good surface to adhere to.

I have used Sandtex Masonry paint, & Dulux Weathershield smooth masonry paint over the years, both lasted well.

Last place had rendered panels under windows, these where primed & painted with Sandtex, 10 years later, paint is still there, hasn't peeled & still looks good.

Thanks Nightglow. Well, I'll go for the Dulux then.
What's the best way to strip the sills?
And that hairline crack, I'm assuming it's the stone not just the paint, so what's the best way to deal with that?

 

[Pug]

painted my entire house (well, repainted) with Dulux weathershield. Went on well, and covered well too - very even finish.