LVP over a concrete slab: what the installation guides require
On a slab, the concrete under the plank decides whether a vinyl floor lasts. Here is what three manufacturers ask for, side by side.
Rigid vinyl plank can float directly over a concrete slab, but only after the slab passes the manufacturer's moisture test and flatness limit. The guides compared here set moisture at 8 lbs by the calcium chloride test (ASTM F1869) and 85 to 90 percent relative humidity (ASTM F2170), and flatness at 3/16 inch in 10 feet. Whether a plastic sheet goes under the planks depends on the brand: Shaw requires 6 mil poly, Mannington says not to use it.
That last point is the reason to read the guide for the exact product in the box rather than a general rule from the internet. Below are the steps in the order they happen on a slab, with what Shaw (Floorte Pro 5, revision 09182024), COREtec (Scratchless, revision 05012023) and Mannington (ADURA Rigid, rev. 03.25.2026) each require.
Why a slab is the hard case
A concrete slab gives off moisture vapor, and a floating vinyl floor sits right on top of it. The two standard tests measure that moisture in different ways. ASTM F2170 is the "Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes". ASTM F1869 is the "Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride".
The manufacturers put the burden on the installer. Shaw's residential warranty: "Any moisture related testing (i.e. relative humidity, pH, and calcium chloride) is the responsibility of the installer." Mannington: "Mannington will not assume responsibility for floor covering failure due to hydrostatic pressure or excessive moisture vapor emission."
Step 1: test the slab
| Guide | Calcium chloride (ASTM F1869) | Relative humidity (ASTM F2170) | If the slab fails |
|---|---|---|---|
| Shaw, Floorte Pro 5, rev. 09182024 | 8 lbs | 90% | "moisture mitigation will need to be completed if testing results exceed product limitations." |
| COREtec, Scratchless, rev. 05012023 | 8 lbs | 90% | "we recommend use of a moisture remediation system." |
| Mannington, ADURA Rigid, rev. 03.25.2026 | 8 lbs per 1,000 sq. ft. per 24 hours | 85% | "additional drying time must be allowed or use of a moisture mitigation system is required." |
Two things follow. The same slab can pass one brand and fail another, so the test result has to be read against the guide of the floor you are buying. And a failed test is answered with drying time or a mitigation system, not with a thicker underlayment.
Step 2: flatten it
Shaw and COREtec both write "Subfloor must be flat - 3/16" in 10' or 1/8" in 6'." Mannington uses the same 3/16 inch in 10 feet and adds a tighter short check: "1/32" (0.8 mm) in 12" (305 mm)".
A floating floor is only as flat as what it rests on, which is why the tolerance comes before anything else. Low spots are filled, and Shaw names the material: "Use cementitious patching and leveling compounds that meet or exceed maximum moisture level and pH requirements."
Step 3: the plastic sheet question
This is where the guides disagree outright. Shaw, for its attached-pad rigid plank: "Installation of 6 mil Poly Film Underlayment is required for floating method over concrete substrates." and "For use over concrete substrates - seams MUST be taped." COREtec calls the same sheet "recommended only for floating applications over concrete subfloors."
Mannington goes the other way: "Mannington does not recommend the use of 6 mil poly directly under ADURA floating products." It also warns against treating the sheet as a fix: "Consequently, Visqueen (6 mil polyethylene) on top of the slab is NOT a recommended solution for controlling moisture emissions above specified limits."
So the honest answer to the vapor barrier question is: use the sheet your product's guide asks for, taped the way it says, and never as a substitute for a slab that failed its test.
Step 4: leave the floor room to move
- Perimeter gap. Shaw: "For areas less than 2500 sq ft, use 1/4" gap For areas larger than 2500 sq ft. use 1/2" gap." Mannington: "ADURA Rigid can be installed up to 50' x 50' (15.2 m X 15.2 m) or total of 2500 sq. ft. (232.3 sq m) with a 1/4" (6.4mm) expansion."
- Transitions. Mannington's ADURA Max guide asks for transitions to be considered at "room size over 50 ft. length or width", and also at substrate and room-to-room environment changes.
- Trim. Shaw: "Undercut all doorjambs. Do not fasten wall moldings and or transition strips to the planks." Baseboard is fixed to the wall, not through the floor.
Step 5: cabinets and kitchen islands
A floating floor has to move, and a cabinet run screwed down on top of it stops that. The guides handle it three ways:
- Shaw allows cabinets on top only if "that area of material must be fully adhered to the subfloor (including an additional 2'ft beyond the cabinets and islands)."
- COREtec: "This product may only be glued down underneath cabinets and at flush mount stairnosing."
- Mannington: "Do not install cabinets or kitchen islands on top of ADURA Rigid."
In a kitchen remodel that decides the order of work: cabinets first and the floor around them, or the floor first with the cabinet area glued, depending on the product.
Waterproof is not the same as slab-proof
A waterproof plank describes the plank. The warranty is narrower. Shaw: "This warranty covers topical moisture as long as the water does not flow over the edge of the surface (edge of the room, cut boards, etc.)." The same warranty "excludes all casualty events normally covered by homeowners insurance including, but not limited to, damages caused by fire, flooding, or standing water from leaking plumbing, faucets, or household appliances."
And it rests on the installation: "The flooring must be installed in accordance with the Company's installation guidelines and specifications." Keep the moisture readings and the product's guide with your paperwork.
Still deciding between vinyl and wood? Our comparison of LVP or engineered hardwood puts the two side by side, slab included. If the floor is part of a bigger job, flooring work in a remodel and a kitchen remodel are covered on their own pages.
Quick answers
Do you need a vapor barrier under LVP on concrete?
It depends on the brand. Shaw requires a 6 mil poly film with taped seams for its floating rigid plank over concrete, COREtec recommends one, and Mannington says it does not recommend 6 mil poly under its ADURA floating floors. Follow the guide for the product you buy.
How flat does a concrete slab need to be for vinyl plank?
Shaw, COREtec and Mannington all ask for 3/16 inch in 10 feet. Shaw and COREtec also accept 1/8 inch in 6 feet, and Mannington adds 1/32 inch in 12 inches. Low spots are filled with a cementitious patching or leveling compound.
What moisture level is acceptable for LVP over concrete?
In the guides compared here: 8 lbs by the calcium chloride test (ASTM F1869), and 90 percent relative humidity by in-situ probe (ASTM F2170) for Shaw and COREtec, 85 percent for Mannington ADURA Rigid. Above that, the slab needs more drying time or a mitigation system.
Can kitchen cabinets sit on top of a floating vinyl floor?
Not by default. Shaw allows it only if that area, plus 2 feet beyond the cabinets and islands, is fully glued to the subfloor; COREtec allows glue-down under cabinets; Mannington says not to install cabinets or kitchen islands on top of ADURA Rigid.
How big should the expansion gap be?
A quarter inch at the walls and fixed objects for most rooms. Shaw asks for 1/2 inch above 2,500 square feet, and Mannington allows ADURA Rigid up to 50 by 50 feet or 2,500 square feet with a 1/4 inch gap.
Does a waterproof LVP warranty cover moisture from the slab?
Read it closely. Shaw's residential warranty makes moisture testing the installer's responsibility, covers topical moisture that does not run over the edge of the floor, and excludes flooding and standing water from leaks. Mannington will not take responsibility for failure from excessive moisture vapor emission.
Sources
- Luxury Vinyl Angle/Angle SPC installation (Floorte Pro 5 Series, attached pad) (Shaw Floors)
- COREtec Scratchless Installation (COREtec (a Shaw / USFloors brand))
- ADURA Rigid Installation Guidelines (Mannington)
- ADURA Max Installation Guidelines (Mannington)
- Residential Resilient Limited Warranty (Shaw Floors)
- ASTM F2170-19a (summary page) (ASTM International)
- ASTM F1869-23 (summary page) (ASTM International)
Read on 2026-10-16.