Every day on my way to the plant in Kishangarh, I pass the same building.

From a distance it looks finished. Painted. Plastered. Done. Get closer and you'll see what I see: white salt crawling up from the ground, render lifting in patches the size of a hand, paint peeling back to expose the putty, the putty exposing the mortar, the mortar exposing the brick.

It's not a slum. It's not an abandoned project. It's a normal building, for normal customers, who paid normal money.

And that is exactly the problem.

The most recent national-level count of what Indian homes are actually built from is still the 2011 Census. The 2021 Census was postponed and has not yet been replaced. So the numbers I'm about to quote are dated — but they are the last full picture we have, and nothing on the ground suggests the story has fundamentally changed.

In 2011, 146 million Indian households lived behind walls of burnt clay brick. Another 66 million lived behind walls of mud or unburnt brick. Together, that was roughly seven out of every ten homes in the country, built on materials that drink water the way dry sand drinks the first monsoon rain.

Fifteen years later, the machine has not slowed down. Under PMAY alone, the government has committed to deliver another 20 million houses between 2024 and 2029. The residential construction market was valued at USD 264 billion in 2025. That is a quarter of a trillion dollars a year being poured into homes. And on a very large share of sites I visit, the wall system hasn't meaningfully evolved.

Here is the sequence I see repeat itself, from Rajasthan down to Tamil Nadu. It isn't the only way people build in this country — good work exists — but it is the default, and the default is what shapes the market.

A mason lays absorbent clay brick. Joints are inconsistent; some tight, many with voids you could slide a finger into. No cavity check. No water test. Nobody is asking whether the wall breathes one way or leaks the other.

Over the raw brick goes a semi-dry mortar render, mixed on site by eye, not by scale. Sometimes with river sand that was never washed. Sometimes with water from the same drum the mason washed his hands in that morning.

Over the render, a thin layer of wall putty. Over the putty, paint. Over the paint, a brochure photograph and a handover.

Eight, twelve, eighteen months later the wall is failing. The owner blames the painter. The painter blames the contractor. The contractor blames the brick. The brick blames the monsoon. Nobody blames the system, because the system has no name.

I'll give it one: we are building sponges, and covering them with wallpaper.

This is the part where a lot of construction-industry writers would reach for a big, emotional statistic and overclaim. I'm not going to do that, because the truth is more interesting.

India has a genuine respiratory health crisis. Around 34 million asthma cases, roughly 13% of the global total, with about three times the global mortality per case. Respiratory disease is, according to a 2024 prescription study covering more than ten thousand Indian doctors, now the single largest disease area in the country — 15.3% of all prescriptions. The state with the highest disability burden from asthma in the Global Burden of Disease data is Rajasthan. The state where I live.

Now: the main drivers of that crisis are not damp walls. They are outdoor PM2.5 pollution, biomass cooking, tobacco, dust. Anyone who tells you otherwise is selling something.

But here is what the building envelope does decide: how much of the air outside becomes the air inside.

A well-designed, well-sealed, correctly rendered wall is a filter. A badly built, cracked, damp, efflorescing wall is a sieve. A 2024 study on housing conditions in Jodhpur — Rajasthan's second-largest city — reported that indoor air in poorly ventilated, poorly constructed homes can run up to ten times worse than the air outside. The World Health Organization has documented for over a decade that living in persistently damp, mouldy buildings raises the risk of respiratory symptoms and asthma by roughly 75%.

The envelope doesn't cause India's air pollution problem. But a bad envelope makes every other thing wrong with the air a little worse, every day, for everyone inside.

That white bloom at the base of the wall — "shora" or "nona" in local language — isn't just cosmetic. It is the wall telling you, in visible handwriting, that water is moving through it, dissolving salts from soil and mortar and brick, and depositing them wherever it evaporates. Every bloom is a confession that the envelope has failed. The occupant doesn't read the confession. They read the peeling paint, and call a painter.

What is the real cost, across ten years, of choosing the cheapest possible wall system?

Not the handover cost. The decade cost. Add up the repainting. The re-rendering. The anti-damp treatments. The plumber trying to find a leak that isn't there because the leak is the wall itself. The inhaler somebody in that house now reaches for at night, a little more often than they used to.

I don't think anyone has ever sent that invoice in full to a single Indian homeowner. If they did, I don't think many would accept a semi-dry render on unprotected brick again.

The man laying that brick on the site I drive past every morning is doing the job he was trained to do, for the price he was told it was worth. He is not the problem.

The problem is a procurement culture that treats the wall as a line item to be minimised, not a system to be engineered. A specification culture where "mortar" means whatever the contractor mixes that morning. A regulatory culture where the brick has a standard, the cement has a standard, the paint has a standard — and the wall, the thing that actually keeps the weather out and the family healthier inside, has no one owning it end to end.

A wall is not a stack of products. A wall is a chemistry problem dressed up as a masonry job. Until the industry — buyers, developers, specifiers, distributors — starts treating it that way, the sponges will keep going up, and the people inside will keep breathing what they breathe.

Walk past one construction site this week. Any one. Look at the wall before the render goes on. Look at the joints. Ask yourself if you'd let your own family live behind it.

Then hit reply and tell me what you saw. I read every one.

Next week: insulation, or the almost complete absence of it, in a country that swings from 48 °C to 4 °C in the same year.

— Guillermo

Built by Chemistry is a free weekly newsletter on the reality of construction chemicals — what works, what doesn't, and what the datasheet won't tell you. Forward it to someone who builds, specifies, or buys. That's how this grows.