- A plumber fixes the pipe and a mitigation company dries the space. We install the new floor after that.
- The EPA says wet materials dried within 24 to 48 hours usually won’t grow mold. Slow leaks are often found much later.
- A patched slab must be flat and within the flooring maker’s moisture limit before anything goes on it.
- Matching old tile is often impossible, so many owners replace the floor across the whole connected area.
What a slab leak is
In most homes here, the water lines and drain lines run in or under the concrete slab. A slab leak is a leak in one of those lines. A burst supply line is the more familiar cousin: the braided hose to a toilet, sink, washing machine or ice maker that gives way and floods a room from above the floor.
They behave differently. A burst supply line announces itself with a puddle, often a big one. A slab leak can run quietly for weeks. Owners sometimes notice a warm spot on the tile from a hot water line, the sound of running water with every tap off, a damp patch or a musty smell near a wall, or a water bill that jumps for no reason.
If you suspect a slab leak, call a licensed plumber. We don’t do plumbing, and we can’t diagnose a leak. What we can do is tell you what happens to the floor once the leak is fixed.
Who does what
A slab leak repair usually involves three trades, in this order:
- The plumber finds the leak and repairs it. Some repairs open the floor and slab above the pipe. Others abandon the old line and reroute a new one through the walls or attic. Ask your plumber which approach they recommend and how much floor it will disturb.
- The water mitigation company removes wet materials and dries the structure. The EPA recommends getting help from experienced professionals where possible.
- The flooring installer, which is us, installs the new floor once the space is dry and repaired.
Patching the concrete after a slab has been opened is usually part of the plumbing repair. Check that it’s included, and that the patch will be finished level with the surrounding slab.
In a condo, the water may have come from the unit above or from a line the association maintains. Talk to the association before any floor work starts. The new floor still needs board approval and the sound-rated underlayment the building requires. We help with the approval paperwork and match the rating your association requires, and we never assume a board will approve.
What the water does to each floor
Different floors respond to the same leak very differently.
- Carpet and pad soak up water fast. UF/IFAS Extension notes that pad is nearly impossible to clean and is normally replaced.
- Laminate with a wood-fiber core can swell at the edges when water reaches it, and swollen edges don’t go back down.
- Ceramic tile usually shrugs off the water itself. It may still have to come up so the plumber can reach the slab, and water can sit in the grout and setting bed.
- Vinyl plank with a rigid SPC core doesn’t swell. On a floating floor, planks can often be lifted to let the slab dry and then reinstalled or replaced.
The EPA says that if wet or damp materials are dried within 24 to 48 hours after a leak, in most cases mold will not grow. A slow slab leak is often found long after that window. Whether any part of the old floor can be kept is a call for the mitigation company and, if a claim is involved, your adjuster. We can’t promise that a water-damaged floor can be saved.
Drying and checking the slab
Concrete holds a lot of water, and it gives it up slowly. The EPA notes that drying usually takes several days to weeks. A new concrete patch adds its own moisture as it cures.
The EPA suggests a simple first check before replacing flooring: tape the edges of a clear piece of plastic sheeting to the slab and wait about 16 hours. If moisture shows on the plastic, the slab is still too wet.
Flooring makers set their own limits. Shaw’s SPC installation guidelines, for example, accept up to 90 percent relative humidity by the ASTM F2170 in-slab test, or 8 pounds by the ASTM F1869 calcium chloride test. The same guidelines ask for a subfloor flat to within 3/16 inch over 10 feet, and they state that the maker does not warrant damage from moisture-related issues. That’s why we check the slab against the limit for your product before we install, and wait if it reads high.
Patch the floor or replace the room
When a plumber opens a trench through a tile floor, the obvious fix is to patch the tile back in. The problem is matching it. Tile from 15 or 20 years ago is usually discontinued, and even a close match can look different next to tiles that have been walked on and cleaned for years.
Many owners decide to replace the floor across the whole connected area instead: the room where the leak was plus the rooms it flows into without a doorway or threshold. With vinyl plank that’s often a single run from the living room through the kitchen and halls, with no seams where the patch was.
If the rest of the tile is sound and flat, some plank makers allow installation over it, with the opened area filled flat first. If tiles are loose or cracked, they come out. Have older tile and mastic tested before anyone tears it out.
Planning for the next leak
Nobody plans for a second leak, but supply lines, water heaters and ice makers are all common sources. Waterproof vinyl plank won’t stop a leak, and it doesn’t make a wet slab dry. What it does is survive a leak on top of it: the core won’t swell, and water can be wiped up.
A few habits help any floor: replace old rubber supply hoses with braided ones, know where your main shutoff is, and consider a leak sensor under the sink and behind the washer. If the house is closed for the summer, turning off the main water supply while you’re away is a simple safeguard. Floodwater is a separate case, and FEMA Technical Bulletin 2 doesn’t list floating vinyl plank among flood damage-resistant materials.
What the new floor costs
We estimate $5 to $12 per square foot installed, before your discount. Our working range is $6.00 to $9.50 per square foot before the discount and about $5.00 to $7.75 after, because the 50% off your flooring installation applies to installation labor. A 200 square foot room is roughly $1,200 to $1,900 before the discount. Try the cost calculator for your rooms.
Leveling a slab patch or removing old tile is priced at the measurement. More on the full job is on our water-damaged floor replacement page, and our guide to replacing floors after a hurricane covers water from above. When the slab is dry, book a free measurement.
Sources: EPA: a brief guide to mold, moisture and your home · EPA: flood cleanup to protect indoor air and your health · Shaw installation guidelines for SPC products · UF/IFAS Extension: cleaning flood-damaged carpets and rugs (DH 524) · FEMA Technical Bulletin 2: flood damage-resistant materials.