Why subfloor prep matters
New flooring telegraphs every bump, dip, and squeak underneath. Laminate clicks together and bridges small gaps — but large low spots flex and crack boards. Tile needs a flat plane or edges crack. Carpet hides minor issues but pad over humps wears faster.
Budget time for prep. It is often half the job on older homes.
Prep checklist
- Remove all old flooring, staples, and adhesive lumps
- Walk the floor — screw down loose OSB or plywood (squeak screws)
- Check moisture: concrete should pass a plastic-sheet or meter test for laminate/tile
- Grind or sand high spots; fill low spots with leveling compound
- Vacuum thoroughly — grit under underlayment wears grooves in laminate back
- For tile on plywood: verify deflection and use appropriate backer board
Concrete vs plywood
Concrete: patch cracks, grind paint or sealer if bonding tile mortar, install vapor barrier or moisture-rated underlay if manufacturer requires it for laminate.
Plywood subfloor: renail or screw on a grid pattern. Joints should not flex. Use underlayment or backer board per product specs — never float laminate directly on bare plank gaps without underlay.
Flatness quick test
Drag a 6–10 ft straightedge in every direction. Mark humps and dips with pencil. Grind highs; fill lows with self-leveler per bag instructions. Re-test before underlay goes down.