Installing LVP Over Concrete

Concrete is one of the most common substrates for LVP, and most products are written for it. The question is never really "can LVP go over concrete" but "does this slab, in its current condition, satisfy what this product requires."

Three things decide that: the physical condition and cleanliness of the slab, its flatness, and how moisture is evaluated and controlled. Everything else on this page supports those three.

The slab has to be sound and clean before anything is measured or installed. Residue from a previous floor, curing compounds, sealers, paint and drywall debris all change what will bond and how the floor sits.

• Remove old adhesive residue, coatings and loose material as appropriate for the slab and the products being used.
• Vacuum thoroughly — grit under a floating floor telegraphs and abrades.
• Check for dusting or a chalky surface, which can indicate a weak slab surface.
• Look for efflorescence or staining, which can point to moisture movement worth investigating.
• Note anything previously coated or sealed; it may affect patching and leveling products.

Not every crack is a problem, and not every crack is cosmetic. The distinction that matters is whether the crack is stable or moving, and whether the surrounding slab is sound.

Slabs are rarely flat enough by accident. Trowel ridges, low areas near drains and perimeters, and humps along old walls are all common. A rigid plank bridges a low spot and rocks on a high one, and both conditions work the joints over time.

• Pull a long straightedge across the slab in several directions, including the diagonals.
• Mark high spots and low areas directly on the slab as you find them.
• Compare what you measure to the flatness requirement in your product's instructions — the acceptable variation is set by the manufacturer, not by a general standard.
• Grind high spots where appropriate; fill low areas with a patch or a leveling product suited to the depth.
• Recheck with the straightedge after prep, before any flooring is opened.

Deeper or widespread low areas are usually a leveling job rather than a patching job. The Self-Leveler Calculator estimates bags from your area, average pour depth and the coverage your product states.

Moisture evaluation matters more over concrete than over any other common substrate, because a slab can move moisture from the ground beneath it long after it looks and feels dry. Slabs on grade and below grade deserve particular attention.

Flooring and adhesive manufacturers specify how moisture is to be evaluated for their products. That typically includes which test methods they accept, what results are acceptable, whether vapor control is required, and which membranes or underlayments are compatible with their system.

Over concrete, a vapor retarder is a distinct requirement from cushioning, and it can apply whether or not your plank has an attached pad. Some attached-pad products permit a specific thin vapor retarder beneath them over slabs; others prohibit anything at all.

• Confirm whether your flooring has an attached pad.
• Check whether a vapor retarder is required over concrete for your product, and to what specification.
• Check how seams are lapped and sealed if a retarder is used.
• If the product allows a separate underlayment, match the approved type and thickness rather than the thickest available.
• Confirm the finished height still works at doors, appliances and transitions.

The full decision is covered in do you need underlayment under LVP?

Freshly placed concrete continues to release moisture well after it is hard enough to walk on. How long a new slab must be in place before flooring is installed, and what must be demonstrated before it is, is set by the flooring and adhesive manufacturers and by the conditions on site.

There is no single waiting period that applies to every slab. Thickness, mix, drying conditions and whether the building is enclosed and conditioned all change the answer, which is why manufacturers set a testing requirement rather than a calendar date.

1. Inspect the slab for condition, cracks, residue and previous coatings.
2. Clean thoroughly and remove anything that will not stay put.
3. Check flatness with a straightedge across the room and diagonally.
4. Mark high spots and low areas as you find them.
5. Address cracks and surface defects as appropriate to what you found.
6. Verify the moisture requirements your product sets, and carry them out.
7. Complete the prep: grind, patch or level as the condition calls for.
8. Recheck flatness and cleanliness, then install.

Floor prep covers the correction methods in general, and LVP subfloor requirements covers what the substrate has to be for any LVP job.

The floor still floats over concrete, so it still needs perimeter clearance and it still must not be pinned. Slabs add one specific wrinkle: fastening transition tracks into concrete is a different operation than into a wood subfloor, and the fastening method comes from the transition system's instructions.

See expansion gaps and transitions and doorways.