What Subfloor Prep Is Needed Before Installing SPC LVT or Laminate
Subfloor preparation is the most important step in any flooring installation. 90 percent of flooring problems trace back to poor subfloor preparation. This guide covers what you need to do before installing SPC, LVT, or laminate.
General Requirements for All Floor Types
Regardless of which flooring you choose, the subfloor must meet three requirements:
1. Flat: maximum 3mm variation over 2 meters
2. Clean: no dust, debris, oil, or old adhesive residue
3. Dry: moisture level within acceptable range
Check these three things before ordering your flooring. If the subfloor does not meet these requirements, fix it before the flooring arrives.
Concrete Subfloor Preparation
Concrete subfloors are common in basements, ground floor rooms, and newer construction. Preparation steps:
Moisture test: Perform a calcium chloride test or use a moisture meter. Acceptable level is below 3 pounds per 1000 square feet per 24 hours. If moisture is higher, install a vapor barrier.
Cracks: Hairline cracks under 2mm wide can be left alone. Wider cracks should be filled with concrete patching compound. Cracks wider than 6mm indicate structural issues that need professional evaluation.
Spalling: Concrete that is flaking or scaling should be repaired with a concrete resurfacer. Remove loose material first.
Slab flatness: Check with a straight edge. Grind down high spots. Fill low spots with self leveling underlayment.
Wood Subfloor Preparation
Wood subfloors are common in upper floors of homes. Preparation steps:
Panel thickness: Subfloor panels should be at least 5/8 inch thick. Thinner panels flex under weight and cause floor movement.
Screw down: If the subfloor squeaks, screw down panels into joists. Use deck screws 1.5 inches long.
Replace damaged panels: Rotting, water damaged, or delaminated panels must be replaced. Do not cover them with new flooring.
Flatness: Plywood panels at different heights need smoothing. Sand high transitions. Fill low panels with plywood patch or leveling compound.
Moisture Requirements for Each Floor Type
SPC: Concrete moisture under 5 pounds. SPC is the most forgiving of the three because the core does not absorb moisture. Vapor barrier recommended but not mandatory.
LVT: Concrete moisture under 3 pounds for glue down. Click lock LVT can handle up to 5 pounds. Vapor barrier recommended for both.
Laminate: Concrete moisture under 3 pounds. Vapor barrier required. Laminate is the most sensitive to moisture and requires the driest subfloor.
Underlayment Selection
Choose underlayment based on your floor type:
- SPC: 1mm to 2mm foam underlayment if needed for sound reduction
- LVT glue down: no underlayment. Use adhesive directly on subfloor
- LVT click lock: 1mm foam underlayment if subfloor is smooth
- Laminate: 2mm foam underlayment with vapor barrier attached
Do not use thick underlayment thinking it will fix subfloor problems. It will not. The floor will sag over time and the locking mechanism can fail.
Professional Tip
Hire a flooring inspector if the subfloor has significant issues. An inspector can assess moisture, flatness, and structural condition. The inspection cost is small compared to replacing a failed floor.
About PROLEADER
PROLEADER provides subfloor preparation specifications for each product line. Contact us for a pre installation checklist specific to your flooring choice.
