My son is in process of having an extension added to a 1920’s/30’s house, the old rendering has been removed and new put on, how long does he need to leave this before painting and what would be the best exterior paint to use.
The old part of the building is not cavity wall and I don’t know what has been used for the rendering. A Straw
Ideally I’d leave it a full year before repainting. If he can’t wait that long than at least 3 months. When a render finish dries out in depth you can get hairline cracks developing which allow water to get in. If you delay painting it gives you a chance to spot these and repair them.
The best kind of coating to use is a mineral based paint like Keim Granital but it’s quite expensive and difficult to apply.
Alternatively a standard emulsion based paint like Dulux Weathershield will suffice.