How to Fix Uneven Plywood Subfloor

Are you planning to put new flooring in your home, but your plywood subfloor is uneven? Don’t worry, with the right tools and techniques, you can easily fix this issue and have a smooth surface for your new flooring. Here’s a step-by-step guide on how to fix uneven plywood subfloor.

An uneven plywood subfloor can lead to many issues, including squeaky floors, uneven surfaces, and reduced stability for your flooring. Whether you’re planning to install new flooring or simply want to improve the existing one, addressing an uneven subfloor is a critical step. This process involves assessing the level of the floor, making necessary adjustments, and ensuring the plywood is properly secured.

In this guide, we will walk you through the essential steps and techniques required to effectively fix an uneven plywood subfloor, ensuring a solid and even foundation for your project.

What are the Causes of an Uneven Plywood Subfloor?

Before we dive into the fixing process, it’s crucial to understand the root causes of an uneven subfloor. Some common reasons include:

• Poor Installation: If the plywood is not installed properly, with inadequate adhesives or incorrect spacing between sheets, it can result in an uneven subfloor.
• Moisture Damage: Exposure to moisture can cause the plywood to warp, leading to an uneven surface.
• Settling of the House: Over time, houses may settle, causing the subfloor to shift and become uneven.

Now that you know some possible causes, let’s move on to fixing the issue.

What Will You Need?

Here are some essential tools and materials you will need to fix an uneven plywood subfloor:

• Pry Bar:  Used to remove any existing flooring or damaged plywood.
• Level: To assess the level of the subfloor.
• Circular Saw: For cutting new pieces of plywood.
• Drill and Screws: To secure the plywood sheets to the joists.
• Wood Shims: Used to fill any gaps between the subfloor and floor joists.
• Construction Adhesive: To ensure the plywood is properly secured to the subfloor.
• Measuring Tape: For accurate measurements of the subfloor and new pieces of plywood.

Once you have all the necessary tools and materials, it’s time to start fixing your uneven plywood subfloor.

9 Easy Steps on How to Fix Uneven Plywood Subfloor

Step 1: Assessing the Subfloor

Before you begin the process of fixing an uneven plywood subfloor, it’s crucial to thoroughly assess the current state of the subfloor. Start by removing any existing flooring materials, such as carpet, tiles, or laminate, to expose the plywood subfloor. Use a pry bar and be careful not to damage the plywood as you remove these materials.

Once the subfloor is exposed, take a level and place it at different points across the subfloor to check for any uneven spots. Move the level around to identify where the floor is not level and mark these areas with a pencil. It’s important to be thorough during this step, as accurate identification of uneven areas will guide the rest of the repair process.

Step 2: Removing Damaged Plywood

After identifying the uneven areas, the next step is removing damaged or warped plywood sheets. Use a pry bar to carefully lift and remove the affected areas. If the damage is widespread, it may be more effective to remove the entire sheet rather than attempting to patch specific sections. Once the damaged plywood is removed, use a circular saw to cut new pieces of plywood that match the dimensions of the removed sections. Make sure the new pieces are of the same thickness as the existing subfloor to maintain consistency. Place the new plywood pieces into position, ensuring they fit snugly without any gaps.

Step 3: Adding Shims to Level the Subfloor

With the damaged plywood removed and new pieces cut, the next step is to level the subfloor using wood shims. Wood shims are thin, wedge-shaped pieces of wood that can fill gaps and create a level surface. Start by placing the level on the subfloor to identify any low spots that require shimming. Insert wood shims under the plywood in these areas, adjusting their position until the subfloor is level. If necessary, use construction adhesive to secure the shims in place and prevent them from moving. This will ensure a stable and even surface for the new flooring.

Carefully check the subfloor level across the entire area and add shims where needed until the subfloor is completely level. This step is crucial for preventing future issues with the new flooring, so take your time to ensure the job is done correctly.

Step 4: Securing the Plywood Sheets

Once your subfloor is leveled with shims, it’s time to secure the new plywood sheets. Begin by laying the new pieces of plywood onto the leveled subfloor. Use a measuring tape to ensure they are properly aligned and fit snugly in place without leaving any gaps. Next, use a drill to insert screws through the plywood sheets into the floor joists beneath. This will secure the plywood in place and prevent any movement. Make sure the screws are evenly spaced, approximately 8 to 12 inches apart along the edges and every 12 inches in the interior sections of the plywood sheet.

Step 5: Sanding the Subfloor

After securing the plywood sheets, the next step is to sand the subfloor to create an even surface. Use a belt sander or an orbital sander for this task. Sand the entire subfloor area, paying special attention to the joints between plywood sheets and any spots where the shims have been added. This will help to smooth out any minor irregularities and ensure a consistent, level surface. Be sure to wear a dust mask and safety goggles to protect yourself from dust and debris. Once you have finished sanding, vacuum the subfloor thoroughly to remove any dust, which will help ensure proper adhesion if you plan to install new flooring.

Step 6: Applying Construction Adhesive

To further ensure the stability and durability of the subfloor, apply construction adhesive between the plywood sheets and the joists. This will help to bond the materials together and prevent any potential squeaking or shifting in the future. Using a caulking gun, apply a generous bead of construction adhesive along the top edges of the floor joists where the plywood sheets will rest. Make sure to cover the entire length of the joists to provide a continuous bond.

Next, lower the plywood sheets into place, pressing them firmly onto the adhesive. The adhesive will help to evenly distribute the load and reduce any minor unevenness that may remain. Allow the adhesive to cure according to the manufacturer’s instructions before proceeding to the next step. Properly applied construction adhesive will create a strong, long-lasting bond that enhances the overall stability of the subfloor.

Step 7: Reinforcing with Screws

After the construction adhesive has cured, it’s time to further reinforce the plywood sheets by adding screws. Begin at the edges of each plywood sheet and work your way toward the center. Use a drill to insert screws through the plywood into the floor joists beneath. Space the screws approximately 6 to 8 inches apart along the edges and about 12 inches apart in the interior sections. This secure attachment will help to maintain the level surface and prevent any movement or squeaking.

Ensure that the screw heads are flush with or slightly below the surface of the plywood to avoid creating any raised spots that could affect the installation of new flooring. Once all screws are in place, double-check the bonds to ensure everything is secure and stable.

Step 8: Installing Underlayment

Before laying down the new flooring, it’s crucial to install an underlayment to provide a smooth, supportive base. Underlayment serves several purposes including noise reduction, added cushioning, and moisture prevention. Start by rolling out the underlayment across the entire subfloor, with the edges of each sheet overlapping slightly.

Use a utility knife to trim any excess underlayment, ensuring that it fits snugly against the walls and around any obstacles. Secure the underlayment using a staple gun, placing staples at regular intervals along the edges and in the middle to prevent movement.

Step 9: Installing New Flooring

Now that the underlayment is securely in place, you can install the new flooring. Follow the manufacturer’s instructions for optimal results depending on the type of flooring you’re using—whether it’s hardwood, laminate, vinyl, or tile. Begin by laying the first row of flooring along the longest wall, ensuring the boards are properly aligned and spaced to allow for expansion. Use spacers if necessary to maintain a consistent gap between the flooring and the walls.

If you’re working with interlocking flooring, click the pieces into place according to the specified method. For nailed-down or stapled flooring, use a flooring nailer or stapler to attach the boards to the subfloor. For glue-down flooring, apply the adhesive evenly on the subfloor as directed and press the boards firmly in place.

Continue laying the flooring row by row, making sure to stagger the seams for a more natural and professional appearance. Use a tapping block and a mallet to ensure each board fits tightly against the one next to it. When you reach the final row, cut the boards to fit, leaving a small expansion gap along the wall.

Once the entire floor is installed, remove any spacers and install the baseboards or trim to cover the expansion gaps. Clean the new flooring according to the manufacturer’s guidelines, and enjoy your newly upgraded space with confidence in its stability and beauty.

By following these steps, you can successfully level a subfloor and install new flooring to create a sturdy and attractive foundation for your living space.

5 Additional Tips and Tricks

1. Use a Floor Leveling Compound: Apply a self-leveling compound to the uneven areas of your plywood subfloor. Follow the manufacturer’s instructions for mixing and application. This compound can fill in low spots and create a smooth, even surface.
2. Sand High Spots: Identify the high spots on the subfloor using a straight edge or a level. Use a belt sander or an orbital sander to gradually sand down these high areas until they are level with the surrounding floor.
3. Replace Damaged Sections: If the unevenness is due to damaged or delaminated plywood sections, consider cutting out and replacing these sections. Use a circular saw to carefully cut the damaged area and install a new piece of plywood of the same thickness.
4. Check for Moisture Issues: Uneven plywood subfloors can sometimes result from moisture problems. Check for any moisture or water damage signs and address the root cause. Ensure the subfloor is dry before making any repairs to prevent future unevenness.
5. Keep an Eye Out for Future Signs of Unevenness: Regularly check your subfloor for any signs of unevenness, such as squeaky or bouncy areas. Address these issues promptly to prevent further damage and maintain a level surface.

With these additional tips and tricks, you can ensure a smooth and level subfloor for your flooring installation project.

5 Things You Should Avoid

1. Ignoring the Underlying Cause: Addressing the symptoms without identifying and fixing the root cause of unevenness can lead to recurring problems. Always investigate why the subfloor became uneven before starting repairs.
2. Using Inadequate Materials: Skimping on quality materials such as leveling compounds, replacement plywood, or adhesives can result in subpar repairs that won’t last. Invest in high-quality products to ensure a durable fix.
3. Rushing the Preparation Phase: Proper preparation is critical to successful repairs. Failing to clean the subfloor thoroughly, skipping the moisture check, or not allowing leveling compounds to cure properly can compromise the integrity of your work.
4. Neglecting Safety Precautions: Working with power tools and chemicals can be hazardous. Always wear appropriate safety gear, such as gloves, goggles, and a dust mask, and ensure your workspace is well-ventilated.
5. Over-Sanding or Over-Filing: Excessive sanding or filing can create new low spots and unevenness. Approach sanding cautiously, taking gradual steps to smooth high spots without removing too much material at once.

By avoiding these common mistakes, you can ensure a successful subfloor repair and a level foundation for your new flooring.

What is the Best Flooring for Uneven Plywood Subfloor?

Choosing the right type of flooring for your uneven plywood subfloor is crucial to achieving a smooth and level finish. Some types of flooring are more forgiving when it comes to imperfections in the subfloor, while others may require additional preparations or be unsuitable altogether.

1. Laminate Flooring: Laminate flooring is a popular choice for uneven subfloors due to its ability to float over minor imperfections. However, it is essential to use underlayment specifically designed for uneven subfloors to prevent the laminate from bending or cracking.
2. Vinyl Flooring: Vinyl flooring is another great option for uneven plywood subfloors. Like laminate flooring, it can be installed as a floating floor and can hide minor imperfections in the subfloor.
3. Engineered Hardwood Flooring: Engineered hardwood is designed to be more stable than traditional hardwood, making it suitable for uneven subfloors. However, it is essential to ensure the subfloor is level within acceptable tolerances before installing engineered hardwood.
4. Carpet or Carpet Tiles: If your plywood subfloor has significant unevenness, carpet or carpet tiles can be a good option. The softness of the material can help mask imperfections and create a level surface.

In conclusion, laminate, vinyl, engineered hardwood, and carpet are all suitable options for uneven plywood subfloors.

What is the Gap Between Plywood and Flooring?

The gap between plywood and flooring can vary depending on the type of flooring you are installing. Generally, it is recommended to leave a 1/4 inch gap between the edge of the subfloor and the flooring material. This allows for natural expansion and contraction of the flooring due to changes in temperature and humidity.

For laminate and vinyl flooring, this gap can be covered with baseboards or quarter-round trim. A larger gap of 1/2 inch may be recommended for hardwood flooring to allow for more significant expansion and contraction.

It is crucial to follow the manufacturer’s recommendations for the specific type of flooring you are installing to ensure proper installation and prevent any issues with gaps in the future. Additionally, it is essential to properly acclimate the flooring material to the room’s temperature and humidity before installation to minimize any potential gaps.

Conclusion

How to fix uneven plywood subfloor requires a combination of careful assessment, diligent preparation, and the right materials. Start by identifying the specific cause of the unevenness, whether it’s due to low or high spots, moisture issues, or damaged plywood sections. Use the appropriate leveling compounds and sand down high areas methodically. Replace any damaged sections and ensure the subfloor is completely dry before proceeding with repairs. Be mindful of potential moisture issues and address them promptly to prevent future unevenness.

Choose suitable flooring materials that can accommodate minor imperfections in the subfloor, such as laminate, vinyl, engineered hardwood, or carpet. Following these steps and avoiding common pitfalls, such as ignoring the underlying cause or using inadequate materials, can help you achieve a level and sturdy foundation for your flooring project.

By dedicating time to proper preparation and execution, you can ensure a long-lasting, smooth surface that will support your flooring choice beautifully.