Other parts of the country get mold from wet basements. Plano gets it from under the floor. Nearly every home here sits on a concrete slab poured over shrink-swell clay, with water and drain lines running underneath. When one of those lines fails, the water has nowhere to go but up into the bottom of the walls, and the first sign is often a smell rather than a puddle. This guide covers why slab leaks are a Plano problem, how to recognize one, what the 24 to 48 hour window really means when the leak is hidden, and how the plumbing job and the mold job fit together under Texas rules.
Why slab leaks are a Plano problem
Collin County lies almost entirely in the Blackland Prairie, and its central and western parts, including Plano, sit on deep clay over marl and chalk. The dominant Houston Black soil is a classic vertisol: it shrinks hard in a dry August and swells back when the October rains come. Water enters it fast when it is cracked and very slowly once it is wet. Builders know this, which is why foundation watering is a recognized North Texas habit and why slab-on-grade foundations are standard. In 2024 about 98 percent of new single-family homes started in the Texas census division were slab-on-grade.
That movement works on under-slab copper and cast iron year after year. Plumbers in Plano report that 1970s and 1980s homes commonly have cast-iron drain lines under the slab that corrode from the inside, and that slab leaks are among the most common plumbing calls in the city. Plano's stock fits the profile: the median home was built in 1993 and 64 percent of units date from 1970 to 1999.
Hot-water slab leaks deserve a mention. A pinhole on the hot side warms the slab and keeps the wall cavity above it humid around the clock. The warm spot on the floor is the classic tell.
Signs of a slab leak, and what each one means
| What you notice | What it often means | Who handles it |
|---|---|---|
| Water bill jumps with no change in use | Supply-line leak under the slab, often hot side | Licensed plumber (leak detection) |
| Warm spot on tile or wood floor | Hot-water line leak heating the slab | Licensed plumber |
| Cupped wood flooring, lifting tile, damp carpet pad | Moisture rising through the slab | Plumber first, then licensed mold assessor |
| Musty smell along a wall or in a closet, no visible leak | Wet bottom plate and back of drywall, possible hidden mold | Licensed mold assessor with a moisture meter |
| Baseboard swelling, paint bubbling near the floor | Drywall wicking water from below | Assessor maps it; remediation contractor opens it |
| Slow drains, sewage smell, soft spots | Under-slab drain line failure (Category 3 water) | Plumber; remediation handles contaminated material |
The 24 to 48 hour window when the leak was hidden
EPA's rule for wet materials is to dry them within 24 to 48 hours to prevent mold. A burst washing-machine hose lets you do that. A slab leak breaks the rule before you know it exists: the water wicks into the bottom plate and the back of the drywall for weeks, and by the time the floor cups or the room smells, the window has passed. So the useful advice is different:
- Treat the discovery date as late. Do not wait for the plumber's schedule to open walls that are already soft.
- Stop the water first. Shut the supply at the meter or the house valve if the bill and warm spot point to a supply leak; a drain leak keeps going as long as you use the fixtures above it.
- Photograph everything before anyone cleans or cuts. Floors, baseboards, the meter reading, the bill.
- Do not scrub a large patch. Under 25 contiguous square feet you may clean it yourself; a wall cavity rarely stays that small once it is opened.
Sewage changes the job. A failed under-slab drain line releases Category 3 water. Porous materials it touched are generally removed rather than cleaned, workers use more protection, and the remediation protocol will say so. Tell the companies up front if the smell is sewage rather than musty.
Two trades, two permits, one order of operations
The mold work and the plumbing work are different trades, and the order matters. No remediation holds while the leak continues, and no Texas assessor will sign a certificate saying the cause was fixed if it was not.
Leak detection and repair
A licensed plumber locates the leak with pressure testing and acoustic or thermal equipment, then repairs it: a spot repair through the slab, a tunnel under it, or a re-route of the line through the attic or walls. Plumbing work and replacing water or sewer lines need a Plano permit, pulled by a city-registered, state-licensed plumber. Confirm current requirements with Plano Building Inspections.
Licensed assessment and protocol
A TDLR-licensed mold assessment consultant maps moisture along the affected walls, decides how much drywall and plate are involved, and writes a protocol. If the area is 25 contiguous square feet or more, the whole licensed process applies.
Remediation under containment
A separate TDLR-licensed remediation contractor files the TDLR notification. Because a delay after water damage would increase contamination, this can be an emergency notification filed the next business day instead of five days ahead. The contractor builds containment, removes wet drywall and insulation, cleans framing, and dries the cavity.
Clearance, certificate and rebuild
The consultant passes clearance, the contractor delivers the Certificate of Mold Damage Remediation within 10 days, and a registered contractor rebuilds the wall and floor, with a permit where walls are replaced. Foundation repairs, if the movement caused damage, are a fourth trade with their own permit.
The slab leak and water damage mold page describes what the companies do on each of those steps, and the process page covers the Texas sequence generally.
What it costs, roughly
Published national ranges for mold remediation run $10–$25 per square foot of affected area (This Old House, March 2026), with 100 square feet typically $1,000–$2,500 and 200 square feet $2,000–$5,000. A licensed assessment is a separate line, typically $303–$1,044 nationally, plus lab fees if air samples are taken. None of that includes the plumbing, the flooring, the rebuild or any foundation work. In a pre-1980 home, ask whether old sheet flooring or joint compound should be sampled for asbestos before tear-out. The Plano mold remediation cost page has the full table and a planning calculator.
Insurance: the words that decide it
Texas homeowners policies generally cover sudden and accidental discharge of water and generally do not cover continuous or repeated leakage, and most do not pay to remove mold except as part of repairing covered damage. Many cap or exclude mold remediation unless you bought an endorsement. A slab leak sits right on that line: the pipe failed suddenly, but the water ran for weeks. Adjusters read the same facts differently, so the paperwork you keep matters. TDI-approved endorsement wording also asks you to report a hidden loss within 30 days of when you detected or should have detected it, so call your insurer as soon as you know. Flood from outside the house is excluded entirely and is a separate NFIP policy. Nothing here is a promise of coverage; our insurance guide goes deeper.
Whoever you hire, verify each license at tdlr.texas.gov/LicenseSearch and ask for the Consumer Mold Information Sheet, proof of $1 million liability insurance and the written protocol before work begins.
Frequently asked questions
How fast does mold grow after a slab leak?
EPA guidance is to dry wet materials within 24 to 48 hours to prevent mold growth. The problem with a slab leak is that the clock usually started weeks before anyone noticed, because the water was under the floor. Treat the discovery date as late, not early, and get the area opened and dried quickly.
Who do I call first, a plumber or a mold company?
A licensed plumber. Slab leak detection and repair are plumbing work, need a Plano plumbing permit, and have to happen before any remediation holds. Once the leak is stopped, a licensed mold assessment consultant maps the moisture and writes the protocol, and a separate licensed remediation contractor does the work.
Will homeowners insurance cover mold from a slab leak?
It depends on the wording. Texas policies generally cover sudden and accidental discharge of water and not continuous or repeated leakage, and many cap or exclude mold remediation unless endorsed. Document everything before cleanup, report the loss promptly once you detect it, and ask your adjuster how your policy treats a hidden leak. Never assume coverage.
Does a slab leak mold job need a permit in Plano?
The mold removal itself usually does not. The plumbing repair, any re-route or re-pipe, foundation repairs and rebuilding walls do, pulled by contractors registered with the City of Plano. Confirm the current rules with Plano Building Inspections, and check with your own city if you are in Frisco, Allen, Richardson or elsewhere.
Want numbers from companies that work in Plano and Collin County? Request free quotes or call (972) 472-8749. Plano Mold Experts is a free quote service, not a mold company or a licensee; independent, TDLR-licensed Texas companies reply to you directly.