To level a floor for a floating floor, you primarily address high or low spots by using a leveling compound or self-leveling screed, or in cases of significant unleveling, by installing a plywood subfloor over the existing one to create a uniformly level surface.
Floating floors, such as laminate, engineered wood, or luxury vinyl plank (LVP), require a very flat subfloor to perform correctly, prevent damage, and ensure a stable, long-lasting installation.
Why Leveling is Crucial for Floating Floors
A properly leveled subfloor is paramount for floating floor installations for several key reasons:
- Warranty Compliance: Most manufacturers' warranties require the subfloor to meet specific flatness tolerances. Failure to level can void your warranty.
- Performance and Longevity: Uneven spots create stress points on the flooring planks, leading to creaking, flexing, gapping, or even board damage over time.
- Appearance: An unlevel floor can result in visible dips, humps, or an uneven surface that detracts from the aesthetic appeal of your new flooring.
- Ease of Installation: Installing floating floors on a flat surface is significantly easier, quicker, and yields better results.
Assessing Your Subfloor's Flatness
Before any leveling work begins, it's essential to accurately assess the current state of your subfloor.
Tools for Assessment
- Long Straightedge: A 6-foot or 8-foot straightedge (e.g., a sturdy board, metal ruler, or specialized floor-leveling tool).
- Feeler Gauges: To measure gaps under the straightedge.
- Chalk Line: To mark high and low spots.
- Measuring Tape: For general measurements.
Flatness Tolerances
Most floating floor manufacturers recommend a maximum variation in flatness. A common standard is:
| Measurement Point | Allowable Variation |
|---|---|
| Per 6 feet | 1/8 inch (3 mm) |
| Per 10 feet | 3/16 inch (4.7 mm) |
How to Check:
- Place the straightedge on the subfloor.
- Slide feeler gauges under the straightedge to measure any gaps.
- Move the straightedge across the entire floor, checking in multiple directions (parallel, perpendicular, and diagonally) to identify all high and low spots.
- Mark identified areas with a chalk line or marker.
Methods for Leveling a Floor
Based on the assessment, you'll choose the appropriate leveling method.
1. Using Leveling Compound or Self-Leveling Screed
This is the most common method for correcting minor to moderate low spots and achieving a very smooth finish.
- Description: A liquid or pourable mixture that, when applied, flows out to create a level, smooth surface before setting. Self-leveling screeds are typically thicker and used for larger, deeper areas, while leveling compounds are versatile.
- When to Use: Ideal for correcting dips, minor undulations, and general unleveling within the manufacturer's specified depth limits (often up to 1-2 inches in a single pour, but check product specifics).
- Process:
- Preparation:
- Clean the Subfloor: Ensure the subfloor is free of all dust, debris, grease, and old adhesive. Vacuum thoroughly.
- Prime: Apply a compatible primer to the subfloor. This helps the leveling compound bond properly and prevents rapid moisture absorption from the compound.
- Seal Openings: Seal any gaps or cracks in the subfloor, especially around vents or pipes, to prevent the compound from leaking through.
- Install Damming: For contained areas or doorways, use foam strips or wood to create a dam if you don't want the compound to flow into adjacent rooms.
- Mixing: Follow the manufacturer's instructions precisely for mixing the compound with water. Use a large bucket and a heavy-duty drill with a mixing paddle to ensure a lump-free consistency.
- Pouring and Spreading: Pour the mixed compound onto the lowest areas first. Use a gauge rake or a smooth trowel to gently guide and spread the compound across the desired area. Work quickly as it sets relatively fast.
- De-aeration (Optional but Recommended): For larger pours, use a spiked roller to remove air bubbles from the wet compound, which helps achieve a smoother, stronger finish.
- Curing: Allow the compound to cure completely according to the manufacturer's guidelines, which can range from a few hours to several days, before installing the floating floor.
- Final Check: Once dry, re-check the area with your straightedge to ensure it meets flatness requirements. Sand down any minor high spots if necessary.
- Preparation:
2. Installing a Plywood Subfloor
This method is suitable for more significant unleveling, structural issues, or when transitioning between different subfloor heights.
- Description: A layer of plywood (or OSB) is installed over the existing subfloor, shimming as necessary, to create a new, flat plane.
- When to Use:
- When the existing subfloor has major humps or valleys that are too deep for leveling compound.
- If the existing subfloor is severely damaged, deteriorated, or uneven (e.g., old, gappy planks).
- When needing to raise the floor height to match an adjacent room or reduce a step-down.
- Over joists that are significantly out of plane, requiring shimming.
- Process:
- Preparation:
- Clean and Inspect: Ensure the existing subfloor is clean and structurally sound enough to support the new layer. Address any squeaks or loose boards.
- Identify High and Low Spots: Use the straightedge method to precisely mark all high and low areas.
- Addressing High Spots: For significant humps in the existing subfloor, consider sanding or grinding them down before installing plywood, if feasible.
- Shimming Low Spots:
- Cut plywood strips or use roofing felt, asphalt shingles, or other thin, stable materials as shims.
- Place shims strategically in the low areas identified, ensuring a gradual slope up to the level plane. You'll typically place shims under the new plywood layer.
- Installing Plywood Sheets:
- Use exterior-grade plywood or OSB, typically 1/4 inch to 3/4 inch thick, depending on the severity of the unleveling and structural needs.
- Stagger the seams of the new plywood layer from the existing subfloor.
- Glue and screw/nail the plywood sheets to the existing subfloor and joists. Ensure screws or nails are long enough to penetrate the existing subfloor and into the joists, if applicable, for maximum stability.
- Leave a small expansion gap (e.g., 1/8 inch) between plywood sheets and around the perimeter of the room.
- Final Checks: After installation, re-check the entire surface with your straightedge to confirm it meets the required flatness for the floating floor.
- Preparation:
By carefully assessing your subfloor and applying the appropriate leveling technique, you can ensure a durable, beautiful, and stable foundation for your new floating floor.
