This article explains the science in plain English. For the complete real estate discussion, including inspections, disclosures, repairs, negotiations, and value, read my pillar guide, Concrete Cancer in Texas Pools: What Austin Area Home Buyers and Sellers Need to Know.
TLDR: What Concrete Cancer Means in a Swimming Pool
- Concrete cancer is an informal name commonly used for alkali-silica reaction, or ASR.
- ASR needs reactive silica, alkalis, and sufficient moisture to develop.
- The reaction can produce a gel that absorbs water, expands, and creates pressure inside the concrete.
- Cracking may be a warning sign, but many other conditions can also cause pool cracks.
- A reliable diagnosis may require engineering review, core samples, petrographic examination, and laboratory testing.
What Is Alkali-Silica Reaction?
Concrete usually contains cement, water, sand, and larger pieces of stone or gravel known as aggregate. Most concrete performs its job for many years without developing ASR. The problem begins only when a specific combination of conditions comes together.
Some aggregates contain forms of silica that can react in the highly alkaline environment inside concrete. Alkalis, primarily involving sodium and potassium compounds, are present in the cement and concrete pore solution. When reactive silica and those alkalis interact, they can form an alkali-silica gel.
That gel can absorb moisture and swell. As the material expands, it may create pressure within the aggregate, cement paste, and surrounding concrete. Concrete is strong under compression, but it does not handle internal tensile pressure nearly as well. When the pressure becomes great enough, microcracks can form and eventually grow into visible cracking.
The Federal Highway Administration explains that ASR can lead to expansion, cracking, increased permeability, and reductions in the strength and stiffness of affected concrete. Its technical materials also explain that the cracks may allow additional moisture to enter, which can contribute to continuing deterioration.
Why Is It Called Concrete Cancer?
The nickname comes from the idea that the deterioration develops within the concrete and may continue progressing over time. The phrase is memorable, but it can also be misleading because it encourages people to treat every crack as proof of the same condition.
A swimming pool can have cracks for many reasons that have nothing to do with ASR. Soil movement, concrete shrinkage, workmanship, inadequate reinforcement, plumbing leaks, hydrostatic pressure, settlement, drainage problems, and ordinary finish deterioration can all produce visible symptoms.
That is why I prefer to use the technical name whenever possible. Saying “possible ASR” reminds us that the condition must be evaluated. Saying “the pool has concrete cancer” sounds like a conclusion has already been reached, even when no qualified professional has examined the pool.
What Three Conditions Allow ASR to Develop?
Professionals often describe ASR as requiring three basic ingredients:
- Reactive silica in the aggregate. Not every type of stone or mineral used in concrete reacts the same way.
- Sufficient alkalis in the concrete. The alkaline pore solution creates the chemical environment in which the reaction may occur.
- Enough moisture. Moisture allows the gel to absorb water and expand.
If one of those ingredients is missing or sufficiently controlled, damaging expansion may not occur. This is one reason construction date alone cannot diagnose a pool. Two pools built during the same month may contain different aggregate, different concrete mixtures, and different levels of exposure.
Why Can Swimming Pools Be Especially Vulnerable?
A swimming pool is a concrete structure designed to hold water continually. Even with plaster, tile, waterproofing components, and proper maintenance, the concrete shell exists in a moisture-rich environment.
That does not mean moisture alone causes ASR. A pool still needs the other ingredients, including reactive aggregate and an alkaline environment. However, when an ASR-susceptible concrete mixture is present, regular exposure to moisture can help sustain the reaction and swelling.
The pool shell is also restrained by reinforcing steel, surrounding soil, decks, plumbing, coping, and attached finishes. Internal expansion may therefore reveal itself through a combination of cracking, movement, separation, finish failure, or water-loss symptoms rather than one universal pattern.
What Might Concrete Cancer Look Like?
ASR can produce visible symptoms, but no single appearance confirms it. Federal Highway Administration field guidance identifies possible signs such as cracking, expansion, localized crushing, joint movement, surface pop-outs, discoloration, and deposits associated with gel or moisture movement.
In a swimming pool, conditions that may deserve further evaluation can include:
- Irregular or map-like cracking
- Cracks that return after repeated cosmetic repair
- Cracking that appears to extend beyond the plaster finish
- Tile, coping, deck, or structural separations
- Bulging, distortion, or unusual movement
- Persistent damp areas, staining, or deposits near cracks
- Unexplained water loss
- A history of repeated plaster failure or structural repair
Those conditions are reasons to ask questions, not reasons to announce a diagnosis. Efflorescence, mineral deposits, ordinary plaster crazing, and soil-related movement can resemble portions of an ASR pattern. A knowledgeable professional needs to consider the complete picture.
Is Every Crack in a Swimming Pool Concrete Cancer?
No. Most people first become worried because they see a crack, but “crack” is a symptom, not a cause.
A small surface crack in plaster may be cosmetic. A structural crack through the shell may reflect movement or construction problems. A leaking plumbing line may create soil movement around the pool. Expansive soil may affect the shell or deck. A poorly detailed joint may separate. ASR is one possible explanation among several.
This is similar to seeing a crack in a home’s wall. The crack tells us something moved, but the appearance alone does not explain whether the cause was normal settling, moisture, framing movement, foundation distress, or a cosmetic issue.
A buyer should begin with a capable home inspector and pool professional, then move to specialized evaluation when the observations justify it. My guide to choosing the right home inspector explains why experience and scope matter more than simply selecting the lowest inspection fee.
Can ASR Be Diagnosed From a Photograph?
No. Photographs can be helpful for documenting changes, comparing crack progression, and showing a specialist what concerns prompted the call. They cannot reliably establish the chemical and physical processes occurring inside the concrete.
A proper investigation may begin with a visual survey and review of the pool’s history. The evaluator may consider the construction date, concrete supplier, prior repairs, water-loss history, crack pattern, movement, environmental exposure, and whether similar concerns have been documented in related projects.
When ASR remains a reasonable possibility, a more complete diagnosis may involve core sampling, petrographic examination, chemical analysis, and testing designed to evaluate current or future expansion. The Federal Highway Administration’s diagnostic guidance emphasizes combining visual observations, field investigation, and laboratory work when necessary.
What Is Petrographic Examination?
Petrography is the detailed examination of concrete and its components, often using prepared samples and microscopy. A petrographer can look for features associated with ASR, including reaction products, cracking around or through aggregate, gel deposits, and other internal evidence.
This kind of examination matters because surface symptoms may be shared by several different problems. Looking inside the concrete can help distinguish ASR from shrinkage, freeze-thaw damage, sulfate attack, ordinary cracking, or other deterioration mechanisms.
Testing should be interpreted by qualified professionals. A laboratory result is not simply a pass-or-fail sticker for the pool. The findings may need to be combined with engineering observations, the pool’s condition, the apparent rate of progression, and the practical consequences for repair or continued use.
Does ASR Stop Once a Crack Is Patched?
Not necessarily. A patch may seal or hide a visible crack without changing the chemical reaction inside the concrete. If reactive materials, alkalis, and moisture remain available, expansion may continue and the crack may return or appear somewhere else.
This does not mean every affected structure must automatically be demolished. Mitigation and repair decisions depend on the extent of damage, expected future expansion, structural performance, moisture exposure, and feasibility of available treatments. Federal guidance recognizes that mitigation may address either the cause of the reaction or the symptoms, and that each option has limitations.
For a homeowner, the practical lesson is simple: do not confuse a better-looking surface with proof that the underlying problem has been solved. Ask who designed the repair, what diagnosis supports it, what part of the structure is being addressed, and what warranty or monitoring plan accompanies the work.
Can ASR Be Prevented in a New Pool?
Prevention begins before the concrete is placed. Concrete professionals can evaluate aggregate reactivity, control the total alkali loading, select appropriate cementitious materials, use qualified mixture designs, and follow recognized testing and specification practices.
Supplementary cementitious materials and other mitigation approaches may reduce the risk in new concrete when selected and proportioned correctly. The appropriate approach belongs to the engineer, concrete producer, materials professional, and pool builder working with the actual project materials.
A future pool owner can ask the builder how the concrete mixture was selected, whether aggregate reactivity was evaluated, what documentation will be provided, and what structural and material warranties apply. Those questions are far more useful than asking for a blanket promise that “concrete cancer can never happen.”
Why Has This Become a Central Texas Real Estate Issue?
The American Society of Civil Engineers published a 2024 forensic engineering paper describing more than 100 pools in and around Central Texas as affected by ASR. Since then, public awareness has continued to grow among homeowners, buyers, sellers, pool contractors, engineers, inspectors, and real estate professionals.
The issue has also reached Texas real estate forms. Texas REALTORS reported that Alkali-Silica Reaction, also known as concrete cancer, was added to Section 3 of its revised Seller’s Disclosure Notice effective June 15, 2026, due to the increasing prevalence of the condition.
That form change does not diagnose anyone’s pool. It does show that known ASR concerns, prior reports, and pool evaluations have become information that sellers and buyers should take seriously during a transaction.
What Should a Buyer or Homeowner Do After Seeing Suspicious Cracks?
Start by slowing the situation down. Do not let a social media post diagnose the pool, but do not cover the crack and forget about it either.
- Photograph the condition and note when it was first observed.
- Gather construction, warranty, repair, service, and inspection records.
- Check whether the crack is changing, returning, leaking, or accompanied by other movement.
- Consult a qualified pool professional experienced with structural concerns.
- Obtain engineering or materials testing when recommended.
- Preserve reports and communications for future disclosure and decision-making.
During a purchase, buyers also need to protect the deadlines in their contract. Specialized testing may take longer than a typical option period, so the buyer should discuss the timing with the real estate broker, inspector, specialists, lender, insurance professional, and attorney as appropriate.
Frequently Asked Questions About Pool Concrete Cancer
Is concrete cancer contagious between nearby pools?
No. ASR is a chemical reaction within a particular concrete mixture. Nearby pools may share materials, suppliers, builders, or construction periods, but the condition does not spread from one pool to another.
Does a pool built after 2017 automatically have ASR?
No. A construction date may justify additional questions, but it does not prove that reactive aggregate was used or that damaging expansion is occurring.
Can pool plaster cause concrete cancer?
ASR occurs within concrete or mortar involving reactive aggregate, alkalis, and moisture. Pool plaster can crack or fail for its own reasons, and a damaged finish may reveal or conceal symptoms, but an ordinary plaster defect is not automatically ASR.
Can a general home inspector confirm ASR?
A general inspector may identify visible concerns and recommend further evaluation. Confirmation may require a pool specialist, professional engineer, petrographer, or laboratory testing.
Does ASR make the pool unsafe?
The answer depends on the extent and location of damage. A qualified professional should evaluate structural performance, water loss, electrical and deck conditions, and any immediate safety concerns.
My Bottom Line
Concrete cancer in a swimming pool usually refers to alkali-silica reaction, a process that can create expanding gel and internal cracking when reactive aggregate, alkalis, and moisture come together. It is a genuine concrete durability problem, but it cannot be diagnosed responsibly from the pool’s age, a single crack, or a photograph.
For buyers and sellers, the best response is evidence. Review the history, inspect the pool, bring in specialists when needed, preserve the documentation, and make decisions based on the actual condition of that particular property.
If you are buying or selling a home with a pool in the Greater Austin Area, I will help you organize the real estate side of that investigation, protect the transaction deadlines, and identify when the question needs to move from a broker to an inspector, engineer, attorney, insurance professional, or other qualified expert.
Sources and Further Reading
- American Society of Civil Engineers: Concrete Cancer and the Central Texas Pool Crisis
- Federal Highway Administration: Alkali-Silica Reaction Overview
- Federal Highway Administration: Alkali-Silica Reactivity Field Identification Handbook
- Federal Highway Administration: Diagnosis, Prognosis, and Mitigation of ASR
- Texas REALTORS: 2026 Forms Updates
You might find Can Concrete Cancer in a Pool Be Repaired? helpful too, since it covers related ground.
