Well if the render is in good condition scrape off all the loose and flaking paintwork and apply a thinned coat of Masonry paint around 10%, it would'nt be a bad idea to give the existing paintwork a sand down either, it may help to dislodge any that is not well adhered. Don't forget to feather any edges to give you a uniform finish, after sanding give the areas a good brush down with a stiff bristle brush.
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