What Goes Wrong with Outdoor Floors

A courtyard, a sidewalk or a balcony has a much harder life than a floor inside the house. The sun heats it at midday and it cools down at night, rain soaks it and it dries out again and again, and people walk on it and drag tables and chairs across it. But most problems start with the same thing: water that doesn't drain away, or that finds a way down.

Where the damage starts

• The joints. The material between the slabs or tiles is the weakest point. Over the years it wears, crumbles and opens up. Water gets under the floor there, and weeds take root.
• The base. Under every floor there is a layer that holds it up: concrete, mortar or screedScreedA layer of sand-and-cement mix or lightweight concrete poured over the slab to create falls and a solid surface for the next material.. When the base stays wet or gives way, the slabs lose their support, rock and break.
• The falls. An outdoor floor is never perfectly flat. It leans slightly so that water runs to a drain, a gutterGutter and downpipeThe channel and pipe that collect rainwater from a roof and carry it down to the ground or the drains. or the street. Where the slopeFalls (drainage slope)The gentle slope built into flat roofs, balconies and bathroom floors so water runs to the drain or gutter instead of pooling. is missing or has been lost, water pools.
• Weeds and moss. Roots widen the 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., and moss holds damp and makes the surface slippery.

This sidewalk shows almost all of it at once. The surface had broken into pieces, moss had spread wherever damp lingered, and weeds were growing in the gaps. A spot like this is easy to trip or slip on.

Signs worth noticing

• Slabs or tiles that rock when you step on them, or sound hollow when you tap them lightly.
• Joints that have gone dark, emptied out or have weeds growing in them.
• Water that sits for hours after rain, or dark marks where water used to collect.
• Cracks that keep growing, and pieces that have sunk or lifted.
• Under a balcony, damp or blistered paint on the ceiling of the floor below.

One cause, many fixes

None of these signs means on its own that the floor has to be redone from scratch. What matters is finding where the problem starts: whether it's only the joints, whether the base has failed, or whether the water has nowhere to go. That can only be seen up close, on site, and it decides which fix makes sense.

The next chapters cover the most common cases: the stone courtyard with tired joints, the sidewalk that has broken along its whole length, and the balcony that holds water.