Uneven floors can complicate furniture placement, create tripping hazards, and even stop you from being able to install a new floor. Whether you’re working with wood, concrete, or tile, we’ll explain how to achieve a smooth, level surface.
Common Causes of Uneven Floors
Before you begin leveling your floor, try to understand what caused the unevenness in the first place. Here are some common causes:
- Foundation settling over time
- Moisture damage causing warping in wood subfloors
- Improper installation of the original subfloor
- Natural characteristics of the building materials used
- Structural issues such as sagging floor joists
Identifying the root cause determines whether you must address any underlying issues before leveling the floor. In some cases, particularly with structural problems, you may need to consult a professional before proceeding.
Tools and Materials Needed for Floor Leveling
Depending on your project, you may need the following:
- Long straightedge (at least 6 feet)
- Measuring tape
- Pencil for marking
- Level (spirit level or laser level)
- Random-orbit sander (for wood floors)
- Angle grinder or floor grinder (for concrete floors)
- Electric drill with a mixing paddle
- Trowels (masonry trowel and wide finishing trowel for smoothing)
- Wet/dry vacuum
- Coarse sandpaper (60–80 grit for wood floors)
- Flathead screws (for wood subfloors)
- Diamond grinding wheel (for concrete floors)
- Self-leveling underlayment
- Underlayment primer
- Cement backer board (for tile installation)
- Polymer-modified thin-set mortar (for tile installation)
Make sure you also have all necessary safety equipment, including a respirator, when working with concrete or wood that may produce fine dust.
Assessing the Floor’s Condition
Identifying High and Low Spots
Before you start leveling, identify your floor’s high and low spots. This helps determine where to focus your efforts.
Start using a long straightedge, such as a level or a straight board. Place it on its edge and move it across the floor in different directions. Look for gaps under the straightedge. Gaps indicate low spots. Then, look for areas where the straightedge rocks. Rocking indicates high spots. Mark these areas with a pencil as you go.
Measuring Floor Unevenness
Once you’ve identified the high and low spots, use your measuring tape to check the gaps under the straightedge at the low spots. Remember, you’re aiming for no more than 3/16-inch variation over a 10-foot span.
For a more precise measurement, use a laser level. Set it up in the center of the room and project a level line across the floor. Measure the distance from this line to the floor at various points to get an accurate picture of the floor’s contours.
Preparing the Floor for Leveling
Proper preparation is key to successful floor leveling. First, clean the floor and remove any debris, dust, or loose material. For wood subfloors, check for loose nails or screws and secure them. Remove any protruding fasteners that might interfere with the leveling process.
If working with a concrete floor, repair any cracks or damage before leveling. For major cracks or structural issues, consult a professional to address the underlying problem.
Finally, if you’re using a self-leveling compound, apply a primer to the floor according to the manufacturer’s instructions. This helps the compound adhere properly to the subfloor.
Leveling Techniques for Wood Subfloors
Sanding Down High Spots
Sanding down the high spots is often the simplest solution for wood subfloors with minor unevenness. Here’s how to do it:
- Use a random-orbit sander with coarse (60–80 grit) sandpaper.
- Start with the highest spots you identified earlier.
- Sand gradually, checking your progress frequently with a straightedge.
- Be careful not to sand too aggressively, or you’ll weaken the subfloor.
- Once you’ve sanded the high spots, vacuum thoroughly to remove all dust.
Adding Plywood Layers
If sanding isn’t sufficient or if you need to raise the overall floor level, adding a layer of plywood can be an effective solution. We recommend this method when you’re transitioning between rooms with different floor heights.
- Choose plywood that’s at least a quarter-inch thick.
- Cut the plywood to fit the room, leaving a quarter-inch gap around the edges.
- Secure the plywood to the existing subfloor using screws every six–eight inches.
- Use thinner plywood or hardboard in some areas to achieve a level surface if necessary.
Leveling Techniques for Concrete Floors
Grinding is the most effective method for concrete floors with high spots. Follow these steps:
- Use an angle grinder for small areas or rent a floor grinder for larger spaces.
- Attach a diamond grinding wheel to the grinder.
- Wear appropriate safety gear, including a respirator and eye protection.
- Grind down the high spots gradually, checking your progress with a straightedge.
- Vacuum thoroughly after grinding to remove all concrete dust.
Self-leveling compounds are ideal for filling low spots on concrete floors. Here’s how to apply them:
- Mix the compound according to the instructions included.
- Pour the mixture onto the low areas of the floor.
- Use a wide trowel to spread the compound evenly.
- Allow the compound to dry completely before walking on it or installing flooring.
Filling Low Spots in Any Floor Type
Self-leveling underlayment is a versatile solution that works on wood and concrete subfloors. Here’s what to do:
- Apply a primer to the subfloor and allow it to dry.
- Mix the underlayment according to the instructions.
- Pour the mixture into the low areas.
- Use a trowel to spread evenly, feathering the edges to blend with the surrounding floor.
- Allow the underlayment to dry completely before proceeding with flooring installation.
For floating floor systems like laminate or some engineered wood floors, you can use builder’s felt to level minor low spots:
- Cut pieces of builder’s felt to fit the low areas.
- Staple the felt to the subfloor, layering it as needed to achieve the desired level.
- Use your straightedge to check that the felt brings the low spots level with the surrounding floor.
Special Considerations for Tile Installation
Level tile involves some extra care. Here’s what to know.
Installing Cement Backer Board
When installing tile over a plywood subfloor, you’ll need to install a layer of cement backer board. This provides a stable, bondable surface for the tile. Here’s how to do it:
- Cut the backer board to fit the room, leaving a quarter-inch gap at the walls.
- Apply a layer of thin-set mortar to the subfloor using a trowel.
- Place the backer board onto the mortar and screw it down every six–eight inches.
- Leave a 1/8-inch gap between boards and fill these gaps with thin-set.
Ensuring Proper Substrate Stability
For a successful tile installation, the substrate must be completely stable. Any flex in the floor can cause tiles to crack or grout to come loose. Here are some tips to ensure stability:
- Check floor joists to make sure they’re adequately supporting the subfloor.
- If necessary, add blocking between joists to reduce flex.
- You may need to add an extra layer of plywood for large format tiles to increase rigidity.
DIY vs. Professional Floor Leveling
You can complete many floor leveling projects yourself. Consider taking the DIY route if the following circumstances apply:
- There’s minor unevenness (less than three-quarters of an inch over 10 feet)
- You’re comfortable using power tools and following detailed instructions
- The project doesn’t involve structural repairs
- You have the time and patience to complete the job thoroughly
Signs You Need a Professional
While DIY is often possible, we advise calling in professional help in these situations:
- The floor has significant unevenness (more than 3/4 of an inch over 10 feet)
- You suspect structural issues, such as damaged floor joists
- The project involves a large area or multiple rooms
- You’re not confident in your ability to achieve a level result
Cost Factors in Floor Leveling Projects
The cost of leveling a floor varies depending on the following factors:
- Size of the area being leveled
- Type of subfloor (wood or concrete)
- Severity of unevenness
- Materials needed (self-leveling compound, plywood, etc. )
- Whether you DIY or hire a professional
Materials for a DIY project generally cost between $3 and $8* per square foot. Professional services typically range from $3–$12 per square foot, depending on the job’s complexity.
*Cost information based on 2024 reports from A-1 Concrete Leveling and East Coast Flooring & Interiors.
