Aluminosis in Spanish apartments: the concrete-cancer problem foreign buyers of 1950–1975 flats need to know about (2026 guide)

Every foreign buyer who ends up looking at Spanish apartments built between roughly 1950 and 1975 eventually meets a Spaniard who lowers their voice and says one word: aluminosis. The buyer nods, doesn't know what it means, files it under "Spanish thing to look up later," and carries on. Six weeks later, an arquitecto técnico is drawing a rebar with a pencil and explaining that the concrete slab holding up their new €280,000 flat is quietly turning into a sponge.

Aluminosis is not common. It is not the norm. Most mid-century Spanish flats are fine. But when it is present, it is expensive, it is legally complicated, and it is the single most consequential thing you can miss on a Spanish property viewing.

This is the guide foreign buyers ask for and rarely get. What aluminosis actually is, why it exists only in a specific window of Spanish construction, which regions and years are exposed, how a surveyor confirms it, what the community has to do once the diagnosis is on paper, and — crucially — how to write your arras contract so the finding doesn't cost you a €30,000 deposit.

The one-paragraph explanation

Between the late 1940s and the mid-1970s, Spanish builders — especially in Catalonia — used a fast-setting cement called cemento aluminoso (calcium aluminate cement, sometimes abbreviated CAC) instead of standard Portland cement. It set in twenty-four hours instead of a week, which was irresistible in a country building housing at the speed of the Franco-era migration boom. It was also cheap. What nobody told the site foremen was that, in humid conditions, cemento aluminoso undergoes a chemical conversion over the following decades: its crystalline structure changes, it loses roughly half its compressive strength, it becomes porous, and — because the process draws chlorides and moisture inward — the steel reinforcement inside it corrodes and swells. That's aluminosis. Foreign readers sometimes hear it called "concrete cancer." The Spanish name is more accurate: it is not a disease of the concrete so much as a slow, invisible failure of the material choice.

Why the problem exists at all

Cemento aluminoso is legal to make. It has genuine uses — refractory linings, mine work, marine repairs where sulphate resistance matters. What it is not suited to is structural concrete in warm, humid residential buildings, which is exactly what most of Barcelona, the Costa Brava, and the Vallès valleys turned it into for a generation.

Spain banned the use of cemento aluminoso in load-bearing structures in 1977, after a warehouse collapse in Barcelona's Poblenou district killed a caretaker and drew official attention to the pattern. The nail in the coffin came thirteen years later, on 11 November 1990, when Block 44 of the Turó de la Peira estate in Barcelona's Nou Barris district partially collapsed. No one was killed only because the residents had already been evacuated after a smaller collapse in a neighbouring block a few days before. The event triggered the largest housing-safety rehousing operation in modern Spanish history — some 2,300 flats across dozens of blocks in Nou Barris eventually had to be demolished and rebuilt — and it made aluminosis a household word in Catalonia.

Since 1977 all new Spanish construction has used Portland-based cements. The problem is entirely confined to buildings that were already up when the ban took effect.

Which buildings are at risk

The population at risk is smaller than the panic sometimes suggests. To carry a real aluminosis risk, a building typically has to tick most of the following:

• Built roughly 1950–1975. Cemento aluminoso appears occasionally as early as the 1940s and as late as 1976, but the risk band is the third quarter of the twentieth century.
• Uses prefabricated concrete beams, particularly the viguetas pretensadas used in mass housing of the era. In-situ poured slabs with Portland cement are not at risk; the aluminate cement was used almost exclusively in factory-made prestressed elements.
• Located in a humid environment. Coastal blocks, ground-floor and low-level flats, buildings adjacent to leaky forjados or perpetually damp bathrooms.
• Located in a region that used aluminoso at scale. Overwhelmingly Catalonia — Barcelona province is the epicentre — with meaningful pockets in Valencia, Alicante, Murcia, coastal Málaga, Bilbao, and parts of Madrid. Interior Castile and the Balearic and Canary Islands used it less. Galicia and Asturias barely at all.

If the flat you are looking at was built before 1950, the risk is essentially zero — cement aluminate was not yet in widespread Spanish use. If it was built after 1977, likewise zero. Between 1977 and 1985 there is a tail of buildings that were already under construction when the ban came in and finished with old-stock beams; treat those with the same caution as a 1970 flat.

The Barcelona neighbourhoods most affected are widely documented: Nou Barris (Turó de la Peira, Prosperitat, Verdún, Roquetes), parts of Sant Andreu, Bon Pastor, La Mina in Sant Adrià, and Ciutat Meridiana. Outside Barcelona, the Vallès Occidental (Sabadell, Terrassa, Rubí) and the industrial belt of the Baix Llobregat carry the same profile. If you are viewing anywhere in these areas and the flat was built between 1955 and 1975, aluminosis is question one, not question ten.

What the surveyor is actually looking for

A peritación técnica by a competent arquitecto técnico is the right tool here — see our Spanish property survey guide for the general playbook. What follows is the aluminosis-specific overlay.

Visual and technical indicators, in the order a surveyor typically checks them:

1. The age and construction system of the building. Recovered from the nota simple, the ficha catastral, and — where available — the proyecto held at the municipal archive. Age plus prefabricated vigueta construction is the flag.
2. Colour of the concrete on any exposed beam. Cemento aluminoso, on drilling, produces dust that is noticeably darker and browner than Portland cement — sometimes described as chocolate-coloured. This is a strong indicator but not proof.
3. Rust staining on ceilings in bathrooms, kitchens, laundry areas or on the underside of balcony slabs. As the rebar corrodes it expands, cracks the surrounding concrete, and eventually pushes reddish-brown stains through the paint.
4. Longitudinal cracks along the underside of beams, running parallel to the length of the beam, often with a hairline width and a slight step. Cracks running across the beam are usually structural but not diagnostic of aluminosis; cracks running along it are.
5. Concrete spalling. Small chunks of concrete that have already fallen off the beam, leaving exposed rebar. If you see this, the diagnosis is essentially made and the question is only how far it has progressed.
6. The state of the neighbours' ceilings. In a communal block, aluminosis rarely affects one flat only. If the community of owners has recently repaired or reinforced beams in the entrances, stairwells, or shared basements, ask why.

None of the visual signs alone is conclusive. Old Portland-cement buildings develop cracks and rust stains too, from ordinary carbonation. The definitive test is chemical.

The €200–€500 test that gives a definitive answer

The test is called a prueba de aluminosis, sometimes an ensayo de carbonatación y de contenido en cemento aluminoso, and it works as follows.

An arquitecto técnico or a specialised lab drills two or three small cores out of the underside of a vigueta — usually in the laundry room, the bathroom or a corridor where the surface can be re-plastered — and takes the samples to a construction-materials laboratory. The lab runs a chemical analysis, typically an oxine test or an X-ray diffraction, that identifies the presence of monocalcium aluminate. The result comes back as one of three categories:

• Negative. No aluminate cement present. Case closed.
• Positive, low conversion. Aluminate cement present but the chemical change is limited; the beam has retained most of its strength. Monitored, not urgent.
• Positive, advanced conversion. Structural strength significantly reduced; intervention required.

Cost: €200–€500 per flat including the report, if you commission it yourself. If the community of owners commissions it for the whole building, the per-flat cost drops sharply.

If you are the buyer and the seller balks at letting you drill three small holes in exchange for the answer to the single most important question about the flat, walk away. That reaction is the answer.

What happens when a block is diagnosed positive

This is where most foreign buyers underestimate the process. A single positive test in one flat does not mean the whole building has to be demolished tomorrow. Spanish law and Catalan technical practice have a defined ladder of intervention, and it plays out over years:

1. Initial diagnosis — the chemical test confirms cemento aluminoso is present.
2. Structural assessment — the community commissions a full informe estructural, testing beams across the building, measuring current load-bearing capacity, and classifying the block as Grade A (monitored), Grade B (localised reinforcement needed), or Grade C (major structural intervention or demolition).
3. Community vote — under the Ley de Propiedad Horizontal the community must vote on remediation works. Structural safety works are legally mandatory and cannot be blocked by dissenting owners.
4. Public funding application — the Generalitat de Catalunya and several other autonomous communities run subsidies specifically for aluminosis remediation. Grants have historically covered 30–70% of the cost, means-tested. The current programme is administered through the Agència de l'Habitatge de Catalunya.
5. Works — reinforcement of individual beams with steel or carbon-fibre plates; wholesale replacement of the forjado; in the worst cases, demolition and rebuild.

The cost per flat is highly variable. Localised reinforcement in a Grade B block runs €5,000–€15,000 per flat over the community. A full forjado replacement in a Grade C block runs €30,000–€60,000. Rebuild-scale interventions on the Turó de la Peira model were funded almost entirely by the public purse; that model no longer exists.

Mortgage and insurance consequences

Two under-appreciated knock-on effects of an aluminosis diagnosis:

Mortgages. Spanish banks, especially the majors, are unwilling to lend against a building with an unresolved aluminosis diagnosis. If you are financing the purchase, the bank's tasador will pick up any recent ITE noting the finding and either refuse the loan or apply a punitive discount to the valuation (10–30% below comparables). If you are a cash buyer, the problem lands on you at resale — the next buyer's bank will refuse in the same way, and the market for the flat contracts to other cash buyers only. See our Spanish mortgage guide for non-residents for the wider financing picture.

Insurance. Most home insurers exclude damage arising from pre-existing structural defects, and specifically exclude aluminosis where it is documented in the community records. That does not stop you insuring the flat, but it does stop the insurance being useful if a beam gives way. In practice this means the community's own seguro decenal and public safety net become the only realistic route to compensation.

The ITE trap. Every Spanish building over 45 years old (in Catalonia, 45 years; other regions vary) must undergo the Inspección Técnica de Edificios (ITE) every ten years. If the ITE report says desfavorable and mentions aluminosis, the finding is in the public record. Buyers and their lawyers can — and should — read the ITE before signing. Ask the administrador de fincas for the most recent one; the community is obliged to keep it. If the seller can't produce it, pull it from the ajuntament directly.

How to write it into your arras contract

The arras contract is where you protect yourself. A standard arras penitenciales contract lets you walk away by forfeiting the deposit (usually 10%). Nobody wants to burn €25,000 because they discovered aluminosis. The fix is a suspensive condition — condición suspensiva — inserted into the arras explicitly:

The parties agree that this contract is subject to the buyer obtaining, within thirty (30) calendar days from signature, a chemical test for the presence of aluminate cement in the structural elements of the property, carried out by a competent architect or accredited laboratory. Should the test return a positive result at any level of conversion, the buyer shall be entitled to terminate this contract without penalty, and the seller shall return the deposit in full within seven (7) days.

This clause is not standard. Spanish sellers and even some notarios will resist it — the argument is always "there is no reason to expect aluminosis in this building." That is the point. If there is no reason to expect it, the clause costs the seller nothing. If they still refuse, ask why.

For belt-and-braces, a second sub-clause covering the ITE:

The seller undertakes to provide the buyer, within seven (7) days of signature, with the most recent Technical Inspection of Buildings (ITE) report. Should the ITE contain a desfavorable qualification not previously disclosed, the buyer shall be entitled to terminate this contract without penalty.

Decision framework: buy, negotiate, or walk

You have the chemical test result. Now what?

Negative. Continue with the purchase. Consider the €200 the best spend of the transaction.

Positive, low conversion, Grade A building. The flat is monitored but structurally sound today. It is a viable purchase if — and only if — the price already reflects the flag. In practice this means a 10–20% discount off the comparable-for-comparable price of an equivalent flat in a non-affected block on the same street. If the seller won't move on price, the flag is not being paid for and you are the one taking the risk.

Positive, advanced conversion, Grade B building. Buyable only if the community has a documented remediation plan with a funded budget, and only if the seller absorbs your share of the estimated cost through a price reduction. Never buy a Grade B flat expecting to fight the community into voting for works after completion — you will lose.

Positive, Grade C building. Walk away. There is no price at which a Grade C flat is a good investment for a foreign buyer. The remediation timelines run five to ten years, the works are disruptive to the point of forcing you out, and the resale market is essentially closed to you until they finish.

The three questions to ask before the offer

If you take nothing else from this guide, ask these three questions of the estate agent, in writing, before you make an offer on any Spanish flat built between 1950 and 1977:

1. Was cemento aluminoso used in the construction of this building, or in any neighbouring building on this block?
2. When was the last ITE, what was the qualification, and can I see the report?
3. Has the community of owners commissioned any structural assessment or remediation works in the past ten years, and are there any decisions pending?

An honest agent will answer all three in writing or, if they don't know, will find out. An agent who deflects, obfuscates or replies verbally only is telling you something. Read our 14 red flags guide for the wider pattern.

The wider point for foreign buyers

Aluminosis is the most dramatic example of a general truth about Spanish property: the age of the building matters more than the condition of the flat. A €500,000 refurbishment inside a 1965 block does not repair the forjado above your ceiling. A pristine kitchen and a marble bathroom are decorative; the viguetas pretensadas holding them up are structural. When you are buying in Spain, especially in Catalonia, especially between 1950 and 1975, your money is buying the building at least as much as the flat.

That is why the reverse-search model works so well for cross-border buyers. When you post a request on Buvivo — "Barcelona, €300k–€400k, minimum 80 m², two bedrooms, no aluminosis, ITE favorable" — agents self-select on the constraint. The ones with a matching, clean, tested building come to you; the ones without stay away. You spend your viewing days on flats that have already passed the question, not on flats where you have to ask it for the first time.

Further reading

• The Spanish property survey (peritación): why foreign buyers keep skipping it — the general survey playbook this article sits inside
• The arras contract in Spain: deposit, penalties, and how to walk away — where the suspensive condition above lives
• 14 red flags every foreign buyer should spot — the wider warning-signs field guide
• Comunidad de propietarios in Spain: what foreign owners must know — because remediation votes happen here
• Buying property in Barcelona: the foreign buyer's guide — the city where aluminosis is a question one item
• Renovating a Spanish property (reformas): permits, contractors, timelines — for when the diagnosis lands mid-purchase

Buyers looking at mid-century Spanish flats: post a request on Buvivo with your constraints — including the ones like "ITE favorable" and "no aluminosis" that no property portal filter captures — and let matching agents come to you.