My built-in planter box on the terrace or by the pool is causing damp. How is it waterproofed from the inside?

Built-in concrete or brick planters on roof terracesFlat roof (roof terrace)The flat concrete roof on top of a building. It is the most common kind of roof in Greece and the part that takes the most sun and rain., balconies and courtyards hold wet soil and plant roots permanently against the masonry. Once their internal lining ages or cracksCrackA split or gap in render, concrete, a wall, a coating or wood. Fine cracks are usually only on the surface; ones that grow, keep reopening or run diagonally need attention., watering seeps straight into the wall or roof slab, showing up as damp patches and peelingPeeling paintWhen paint loses its grip and lifts off in flakes or sheets. It is almost always a sign of a problem underneath, usually damp or poor preparation. paint on the outside or on the ceiling below.

No exterior patch will hold unless the planter is sealed from the inside. In this terrace planter, all plants and soil were removed down to the bare floor. After thorough cleaning, a grey base waterproof coat was worked across the bottom and into the corners, followed by white waterproof coatingElastomeric waterproof coatingA thick, rubbery waterproof paint for flat roofs, parapets and roofs. It stretches without cracking as the building expands and bridges hairline cracks. all the way up the inside walls.

In a set of long planters beside a swimming pool where the old lining had peeled away, the failed layer was stripped out completely, the floor was prepared and new waterproof coats were applied across the floor and walls, taking care to seal around the drainage outlets while keeping them open so excess water can drain away.