The first contact

Tell him how to find out whether he needs you at all.

Published 2026-08-22 5 min read

The short answer

Tape a square of plastic to the wall and wait a few days. Wet on the wall side means water is coming through; wet on the room side means condensation. The two need different work.

He calls because the basement smells and there is a dark patch on the wall. He has already decided what it is, because everyone knows what a wet basement means: water is getting in.

Sometimes it is. Sometimes it is warm air meeting a cold wall and leaving its moisture there, which is a different problem with a different, usually cheaper answer. Both produce a damp patch and a smell, and standing in the room looking at it does not reliably tell you which one you have.

The square of plastic

Tape a piece of clear plastic to the wall, sealed on all four edges, and leave it for a few days. Then look at which face is wet. Moisture trapped between the plastic and the wall came out of the wall. Moisture on the room side came out of the air.

It costs nothing, anyone can do it, and it separates the two cases in a way no amount of describing the smell over the phone ever will.

Which face of the plastic is wet is the answer. Nothing else about the patch tells you as much.

Why put this on your website

Because some of the people who do it will find condensation and never call you. That is the honest cost, and it is smaller than it looks. They were not going to be good jobs — they were going to be a visit, a diagnosis they did not want to hear, and a customer who suspects you talked yourself out of work you could not do.

And the ones who find water under the plastic arrive knowing they have a real problem, having proved it themselves. That is a completely different conversation from the one that starts with somebody hoping you will say it is nothing.

What the test does not tell you

It says where the moisture came from. It does not say where the water enters, how much of it there is, or what it would take to stop. That is your work, and saying so plainly on the same page keeps the test from being mistaken for the whole diagnosis.

It is also worth naming the third case, because it exists and it confuses people: both at once. A wall that is genuinely wet and a room that is also too humid will show moisture on both faces, and that is worth a visit rather than a guess.

Five sections and what each prevents. Our own reasoning, from how these calls usually arrive.
What the page says	What it prevents
The plastic test, described in three sentences	A phone call in which two different problems are described with the same words.
That condensation is a real answer, not a brush-off	The customer who thinks he is being turned away.
What the test cannot tell him	A homeowner acting on half a diagnosis.
The both-at-once case	A confusing result read as a failed test.
What you actually do on a first visit, and what it costs	The suspicion that a visit is a sales call in disguise.

The diagnosis block — copy it and put your own visit terms in the brackets

Heading, in his words: “Is my basement leaking, or is it just damp?”
The test, in full: “Tape a piece of clear plastic to the wall — sealed on all four edges — and leave it a few days. Then look at it.”
Reading the result: “Wet between the plastic and the wall: moisture is coming through the wall. Wet on the room side: it is condensing out of the air. Wet on both: you have both, and that is worth us looking at.”
What each one means for him: “Water through the wall is [what you do about it]. Condensation is usually [ventilation, heating, a dryer vented outside] — and that is often not a job for us at all.”
The honest limit: “The test tells you where the moisture came from. It does not tell you where it gets in or what it costs to stop. That is what we come and find out.”
The visit, priced: “A first visit is [$X or free], takes about [time], and you get [what: written findings, photographs, options] whether or not you go ahead.”
What you will not do: “We do not [quote for work before seeing which problem it is / sell a system on the phone].”

The fourth point is the one that costs you jobs and earns you the trade. Writing down the case in which the answer is “not us” is the fastest way to be believed about the case in which the answer is you.

Why there are no numbers here

You will find pages giving humidity readings, moisture-meter thresholds and a precise number of hours to leave the plastic up. This one does not, because the useful part of the test is not a measurement — it is a side. Wall side or room side. A figure would make it look scientific and give a homeowner one more thing to get wrong.