New, smooth concrete is too slick. You need to etch it. Use a liquid concrete etcher (muriatic acid alternative) or simply use a bonding primer made for masonry. This creates "teeth" for the paint to grab onto.
Painting concrete window sills is a weekend afternoon project that delivers a “new house” feeling. Just remember: clean it, etch it, and use the right paint. Do that, and your sills will outlast your mortgage. painting concrete window sills
Here’s the good news: painting your concrete window sills is one of the cheapest, fastest, and most satisfying DIY projects you can do. It’s the “lipstick” of exterior home maintenance. But—and this is a big but—concrete is a diva. If you slap any old paint on there, it will fail faster than a New Year’s resolution. New, smooth concrete is too slick
And how to do it so the paint actually sticks (for more than a week). This creates "teeth" for the paint to grab onto
Elias stared at the window sill, his knees popping as he crouched. It was a slab of concrete, poured forty years ago when the house was built. Over the decades, it had turned a sickly, nicotine-stained yellow. It was chipped, pockmarked by the stray hailstones of a thousand storms, and stained by water runoff from a faulty gutter that had been fixed too late.
When choosing a paint for concrete window sills, it is essential to select a paint that is specifically designed for use on masonry surfaces.