Terrace waterproofing in Mallorca

Waterproofing a terrace means placing a continuous watertight layer between rainwater and the structure of the building, and carrying that water to a drain without letting it stop on the way. It sounds simple and it often fails, because water does not get in through the surface of the terrace but through the details: an open tile joint, a badly finished drain, a crack in the parapet, a fall that does not exist. This page explains why terraces in Mallorca leak, which systems exist and how we decide between applying over the existing floor and lifting it.

Why a terrace leaks

• Spent or missing membrane. Many terraces from the seventies to the nineties have a bituminous felt that has reached the end of its life, and quite a few have nothing at all between the tiles and the slab. Bedding mortar is not waterproof; it holds water and lets it through slowly.
• Cracked and hollow tiles. A broken tile lets water in; a tile that sounds hollow is a reservoir of water underneath looking for a way out.
• Joints. The cement joint between tiles is the weak point of any tiled terrace: it cracks with summer expansion and is where most of the water enters.
• Drains and downpipes. A drain without a reinforcing collar, with a membrane that does not go down into the pipe, or blocked with pine needles, is the most common cause of the stains that appear in one corner of the ceiling below.
• Parapets and junctions. Water gets in through the crack between floor and wall, through the parapet coping or under the door threshold, and shows up far from where it entered.
• No fall. If water ponds, it sits on the membrane for hours and finds any pore. The torrential autumn rain in Mallorca tests all of the above in a single afternoon.

Waterproofing systems

Liquid membranes

Applied by roller, brush or spray, they form a continuous, jointless layer that follows drains, corners and parapets. They are the usual system when working over the existing floor.

• Liquid polyurethane. The reference for walk on terraces: elastic, UV resistant in its aliphatic version, 1.5 to 2 millimetres thick in two or three coats, reinforced with mesh at critical points. It takes a walk on finish, coloured or clear, and a new floor on top.
• Polyurea. Hot spray applied with specialist equipment and cured in minutes, which makes it possible to waterproof and return a terrace to use in one day. Very tough, normally 2 millimetres. We choose it on large community roofs or when the timetable is tight.
• Fibre reinforced acrylics. Cheaper and easier to apply, with less elasticity and a shorter life. We use them on non walk on roofs, for spot repairs and as maintenance over a compatible earlier system.

Sheet membranes

Bituminous sheets and synthetic PVC or TPO sheets are welded or bonded and protected with a screed and new tiles, or left exposed on non walk on roofs. They are the classic system when the floor is lifted and the terrace rebuilt with new falls. They give a guaranteed thickness and a very long life, at the cost of more building work.

Over the tiles or lifting them

If the substrate is sound, the tiles are firm, the fall carries water to the drain and the drains work, a liquid membrane over the existing floor solves the leak with little disruption and in a few days. If there are hollow tiles over a wide area, the terrace has no fall, the slab is damaged or the drain sits above floor level, the honest answer is to lift, rebuild the falls with a lightweight screed, lay a sheet or liquid membrane on the new substrate and finish with tiles, stamped concrete or microcement. We tell you at the visit, with the hollow tile test and the spirit level in hand.

Finding the leak

Before waterproofing, you need to know where the water is getting in, because a perfect membrane across the whole surface does not close a badly finished drain. We look at the stain below and place it on the plan of the terrace; we tap the tiles to hear the hollow ones; we check joints, parapets, copings, thresholds and the junction of the membrane with each downpipe; and where necessary we run a flood test by zones, plugging the drain and filling the terrace with a few centimetres of water to see where and when it appears below. On large community terraces, the leak is often metres away from the stain.

The flat below

Damp on the ceiling of the property below takes time to dry out after the water entry is fixed: weeks, and months if the slab has been saturated for a long time. Until the ceiling is dry it is not worth painting or repairing the plaster, because the stain comes back. We document the condition before and after, which helps with the community or the insurer when the terrace is for private use and the damage is in another property.

Falls and drains

The trade rule is a minimum fall of 1 to 2 percent towards the drain, with no back falls and no puddles. Each drain gets a reinforcing collar into which the membrane laps and goes down the pipe, and a grating that holds back leaves and pine needles without blocking the flow. Where a terrace has a single drain, we recommend an overflow through the parapet: if the drain blocks during a storm, the water goes out there and not through the living room door. If the terrace has no fall, one is formed with a lightweight screed before the membrane, which means lifting or building up.

Flat roofs and community roof terraces

On non walk on flat roofs, the priorities are durability under the sun and watertightness around chimneys, aerials and air conditioning units. We work with light coloured polyurethane or polyurea, which lowers the roof temperature, or with protected exposed sheet. For residential communities and property administrators we prepare a specification with the system, thicknesses, phases and guarantee, and organise the work so that the flats below lose access to the terrace for as short a time as possible.

About the guarantee

Every system we apply is handed over with a written guarantee stating the product, the thicknesses and the maintenance conditions that keep it valid: clean drains, nothing drilled through the membrane, the parapet seals checked. Its length depends on the system chosen and is set out in the quote, not here, because it is not the same for a maintenance acrylic as for a 2 millimetre polyurethane or a polyurea.