Slabs make a solid base for luxury vinyl plank, but they hold and release moisture in ways that aren’t obvious from looking at them. That’s why moisture testing is worth considering when preparing a slab for new flooring.
This guide covers why waterproof planks don’t solve moisture coming up from below, what a moisture test looks at, when a vapor barrier or underlayment makes sense, and how it all fits into floor prep and leveling.
Waterproof Planks vs. Moisture From Below
You can read more about this product on our waterproof vinyl plank flooring page.
The word “waterproof” describes the plank, though, not the whole floor system. Water spilled on top mostly stays on top. Moisture rising from the slab works from the bottom up, and that can cause problems that have nothing to do with whether the plank itself absorbs water.
Excess slab moisture can:
- Get trapped between the slab and the flooring, where it has nowhere to go
- Weaken the bond of glue-down installations
- Contribute to musty odors or mold growth underneath the floor
- Affect some underlayments and pad materials
So a waterproof plank is a good start, but it doesn’t replace checking what’s going on in the concrete underneath.
Why Florida Slabs Deserve a Closer Look
This isn’t about scaring anyone. Plenty of slabs test fine. But a few things make testing a sensible step:
- Removing old flooring. What a slab was doing under the old floor isn’t always clear until it’s checked.
Testing up front is easier than dealing with a floor problem later.
What Moisture Testing Checks
Moisture testing measures how much moisture is in the slab or coming off its surface, so it can be compared against the requirements of the flooring and any adhesive being used. Flooring manufacturers set their own limits, and those limits vary by product.
The right approach depends on the project and the product.
Testing also gives a chance to look at related issues, like:
- Areas near exterior doors, sliders or bathrooms that may read differently than the rest of the house
- Leftover thinset or adhesive that could affect how the floor sits
- Cracks or patches worth paying attention to
The goal is simple: know what you’re working with before planks go down.
When a Vapor Barrier or Underlayment Is Used
The test results, the type of LVP, and the manufacturer’s instructions all shape the next step. In general:
- Readings within the product’s limits. The installation can usually move ahead as planned, using whatever underlayment the manufacturer calls for. Some planks have an attached pad; others need a separate one.
- Readings that call for extra protection. A vapor barrier may be used to help keep rising moisture away from the planks.
- Glue-down installations. These rely on the adhesive bonding to the concrete, so moisture levels matter a lot. Any products used must match the flooring manufacturer’s requirements.
Rock Solid LVP installs both click-lock and glue-down LVP, as well as luxury vinyl tile, so the method can be chosen based on your slab and your goals rather than forcing one approach on every home.
If you bought your own flooring, we’ll look at the manufacturer’s installation instructions for your specific product. Rock Solid LVP installs customer-purchased flooring, and following those instructions on moisture and underlayment is part of doing it right.
How Moisture Testing Fits Into Floor Prep and Leveling
Moisture testing is one piece of a bigger prep process. A good LVP floor depends on what’s under it, and that usually means:
- Removal of the old flooring, including tile and thinset
- Moisture testing of the exposed slab
- Leveling low spots so the planks sit flat and lock properly
- Vapor barrier or underlayment as needed
- Installation and trim, including baseboard and quarter-round
With Rock Solid LVP, one crew handles removal, prep, installation and trim. You can learn more about this stage on our floor prep and leveling page.
Notes for Condo Owners
Condo associations often have rules about flooring and what goes underneath it. Rock Solid LVP is licensed and insured, can provide certificates for condo associations and property managers, and helps with condo association approval paperwork. Ask your association about its requirements early so prep and materials can be planned around them.
Get a Clear Answer About Your Slab
Family-owned and based in Port Charlotte, Rock Solid LVP brings 30+ years of flooring experience to homes and condos in Port Charlotte, Punta Gorda, North Port, Venice, Sarasota, Bradenton and Cape Coral, across Charlotte, Sarasota, Manatee and Lee counties. We offer free in-home estimates with clear written pricing, and we’ll talk through moisture testing, prep and installation honestly, with no pressure.
To schedule your free in-home estimate, call (941) 555-0137 or contact Rock Solid LVP.
Frequently Asked Questions
If I'm installing waterproof vinyl plank, do I still need moisture testing?
It's a good idea. Waterproof planks resist water from above, but moisture rising from a concrete slab can get trapped under the floor or affect adhesives and underlayments. Testing shows whether extra protection like a vapor barrier is needed.
Is a vapor barrier always required under LVP on concrete?
Not always. It depends on the moisture readings, the type of plank, whether it's click-lock or glue-down, and the manufacturer's installation instructions. Some planks have an attached pad and others call for a separate underlayment or barrier.
Can Rock Solid LVP install flooring I bought myself?
Yes. Rock Solid LVP installs customer-purchased flooring and will follow that product's manufacturer instructions for moisture, underlayment and installation.
Does Rock Solid LVP help with condo association requirements?
Yes. Rock Solid LVP is licensed and insured, can provide certificates for condo associations and property managers, and helps with condo association approval paperwork.