It rains little here, and badly: months go by without a drop and then half a year’s rainfall arrives in a few hours. That pattern is the worst possible one for a roof, because the drains silt up with dust during the dry spell and the water arrives all at once, in volume, looking for any weak point. That is why leaks in this province always appear on the same day: the first heavy storm.
At Grupo Construcciones Alicante we waterproof roofs, terraces, basements and buried structures across Alicante and the province. The first job is finding where the water actually gets in, which is rarely where the stain appears; then the system is chosen, and above all the junctions and drainage outlets are properly resolved, because that is where ninety per cent of waterproofing fails.
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A leak never stays as a stain. Water entering through the roof travels along the slab, comes out wherever it finds a way and along the route corrodes reinforcement, brings down plaster and ruins the suspended ceiling and the wiring running through it. The longer it takes to act, the more expensive the repair, and there comes a point where structural damage is what drives the budget.
Waterproofing properly once works out cheaper than patching every rainy season. And if you take the opportunity to insulate at the same time (an inverted roof places the insulation above the membrane, protecting it from temperature swings), you solve two problems with one set of access equipment and one job, while extending the life of the waterproofing itself.
Water allows no shortcuts. This is the order we follow on every job:
We locate the actual point of entry, which is almost never above the stain: we check drains, junctions with upstands, expansion joints and service penetrations, and carry out a flood test if needed.
A fixed quote with the chosen system, the area, the treatment of junctions and outlets and the reinstatement of the paving if it has to come up.
We prepare the substrate: cleaning, cutting back, forming or correcting the falls and sealing cracks. No system bonds to a dirty substrate or one with standing water.
We apply the membrane taking particular care over the difficult details: dressing into upstands, reinforcement at drains and corners, and sealing every service penetration.
We carry out a watertightness test, flooding the area for as long as needed and checking underneath, before laying any finish over the top.
We reinstate the paving or the intended finish, leave the drains clear and accessible and provide the written guarantee for the system installed.
Bituminous sheet. The classic and highly reliable system for flat roofs. Laid in one or two layers, with welded laps and reinforcement at the junctions. It needs protection from the sun (gravel, paving or mineral surfacing), because ultraviolet radiation is what ages the material.
Liquid membranes and polyurea. Applied to form a seamless continuous layer, adapting to any shape. They are the ideal solution on roofs with many elements to work around (flues, plant, service penetrations) and on irregular surfaces where sheet material would require too many cuts. Polyurea also cures very quickly and can be walked on the same day.
Waterproofing mortars. For buried walls, basements, tanks and pool shells, where the material must bond to the substrate and resist water pressure, including from the negative side. They are combined with reinforcing bands at wall-to-slab junctions.
Inverted roof. The insulation sits above the waterproofing, protecting it from thermal shock, which is its main enemy. Gravel or floating paving goes on top. It is the most durable solution for a flat roof, and what we recommend when the whole roof has to be redone.
Failure is almost never in the middle of the field, which is the easy part: it is at the junctions. The membrane dressed into the upstand without enough height, a drain without its reinforcing collar, an expansion joint resolved by eye, a cable or pipe penetration sealed with silicone. That is where water gets in, and it is why cheap waterproofing tends to last two winters: the savings come precisely from the details that hold the whole system together.
The second critical point is the falls. A flat roof is not flat: it must fall towards the drains. If water ponds, any system eventually fails and, meanwhile, the weight of the standing water loads the slab. Where we find areas where water sits, we form falls before waterproofing, even if that means more work.
And one piece of maintenance advice that saves a great deal of trouble: clear the drains and gutters before autumn. In a province where months of rain can fall in one afternoon, a drain blocked with leaves and dust turns a sound roof into a swimming pool. It is half an hour’s work once a year.
Waterproofing work we carry out regularly in Alicante and the province:
Not always. If the substrate is sound and the falls are correct, a liquid membrane can be applied over the existing paving after cleaning and priming it, with a new finish on top or left exposed. It is quicker and cheaper. However, if there are loose tiles, water is already trapped beneath the paving or the falls are wrong, it has to come up: waterproofing over a layer that already holds water achieves nothing.
Methodically, because water travels along the slab and emerges far from where it enters. We first inspect the usual suspects (drains, junctions with upstands, joints and service penetrations) and, if nothing shows, we run a flood test zone by zone, blocking outlets and watching from below. Only once you know where the water gets in does repairing make sense; patching the stain is the surest way to be back next year.
A properly executed system, protected from the sun, lasts between fifteen and twenty-five years. What shortens that life is direct ultraviolet radiation on the membrane, ponding water from inadequate falls, and substrate movement without joints to absorb it. That is why roofs with the membrane exposed to the sun age far sooner than those protected with gravel or paving.
Yes, provided you don’t apply to a damp substrate or with rain forecast in the following hours, and you respect each product’s minimum temperatures. In this climate there are workable windows practically all year. What you should not do is apply over a substrate that hasn’t dried after rainfall, however urgent the repair.
In basements and car parks the water pushes from outside inwards, known as negative pressure, and not every product will do: specific waterproofing mortars capable of resisting that pressure are used, treating the junction between wall and slab, which is usually where it appears. Where the problem is severe, the definitive solution also involves work on the external drainage of the wall.
It depends on the building’s configuration and the association’s rules. As a general principle, a terrace that acts as the roof of the building is treated as a communal element in that function, even where its use is private, and maintaining the waterproofing usually falls to the association, while the paving and elements of exclusive use belong to the owner. Every case has its nuances, so it is worth documenting the source of the damage properly before raising it at the owners’ meeting.