Damp on our ceiling shows up right under the terrace railings or columns. How are their bases sealed?

Metal railings, awning or pergolaPergolaAn open shade structure in a garden, on a terrace or a roof, made of posts and beams with slats, reeds, fabric or plants on top. It is often made of wood. posts and columns on a roof terraceFlat 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. or balcony are prime leak points. Metal heats up, cools down and flexes in the wind differently from the concrete or tiles around it. As a result, rigid mortar at the base 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., the iron rusts and expands, and water runs straight down along the post.

Plain cement mortar at these spots simply cracks again. On this roof, where the old seals around the metal posts had split, each base was cleaned, given a first coat of waterproofingWaterproofingThe work and materials that stop water getting through on flat roofs, balconies, bathrooms, basements, planters and tanks., wrapped with reinforcing fabricReinforcement meshA mesh or fabric, usually glass fibre or polyester, set into render, a coating or liquid waterproofing to hold it together and stop cracks from opening. carried up onto the metal post itself, and finished with top coats of flexible membrane.

On another tiled terrace where water was getting in around the columns and walls, the tiles right around each column were broken out to open a clean channel down to the slab, pressure-washedPressure washingCleaning a surface with a strong jet of water from a machine. Before waterproofing, insulation or painting, it removes dust, dirt, lichen and loose material so the new layer bonds well., and sealed with reinforced 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..