How To Fix High Spots In Subfloor

Are you planning to install new flooring in your home? Before you do, it's essential to ensure your subfloor is level.

High spots in your subfloor can cause your new flooring to be uneven, leading to issues down the line. Luckily, fixing high marks on your subfloor is a relatively easy DIY project.

Worker installing the subfloor

One technique for fixing a high spot in your subfloor is to pull up the subfloor and shave down the top of the joist. However, this can be a time-consuming and messy process.

Another method is to use a self-leveling compound to even out the subfloor. This is an excellent option if you have multiple high spots or if you want to avoid the mess of shaving down the joist.

Understanding High Spots in Subfloor

High spots in the subfloor can cause your new flooring to be uneven, leading to problems down the line. But what exactly are high spots in the subfloor, and how can you fix them?

High spots in the subfloor refer to areas where the subfloor is higher than the surrounding areas. This can be caused by several factors, including uneven joists, warped plywood, or simply an accumulation of debris or adhesive.

High spots can be particularly problematic if you're installing a floating floor, as these types require a level subfloor to prevent movement and buckling.

Identifying High Spots

1. Use a Level

Using a level is one of the easiest ways to identify high spots in your subfloor. Lay the story on the floor to see if it's level.

If the bubble in the level is off-center, you have a high spot. You can use a pencil to mark the high place to know where to focus your attention.

2. Shine a Light

Another way to identify high spots is to shine a light across the floor. High marks will cast shadows, which will help you determine where they are.

You can use a flashlight or a work light to shine across the floor and mark the high spots with a pencil.

3. Walk on the Floor

Walking on the floor can also help you identify high spots. You probably have a high spot if you feel like you're walking on a slope or if the floor feels uneven.

You can mark the high spot with a piece of tape or a pencil so that you know where to focus your attention.

Once you've identified the high spots in your subfloor, you can move on to fixing them. The following section will cover different ways to improve high marks on your subfloor.

Tools and Materials Required

When fixing high spots in the subfloor, having the right tools and materials is crucial. Here is a list of items you will need to get the job done:

Basic Tools

  • Tape measure
  • Carpenter's square
  • Circular saw
  • Reciprocating saw
  • Drill
  • Hammer
  • Pry bar
  • Chisel
  • Screwdriver
  • Level
  • Safety glasses
  • Gloves

These basic tools are essential for any DIY project, including fixing high spots in the subfloor. Make sure you have them on hand before you start.

Specialized Tools

  • Floor scraper
  • Belt sander
  • Handheld sander
  • Floor buffer
  • Pry bar with nail puller
  • Joist jack
  • Wood shims
  • Self-leveling compound

These specialized tools may not be necessary for every project, but they can make the job easier and more efficient.

For example, a floor scraper can help remove old adhesive or debris from the subfloor, while a belt sander can quickly level out high spots.

A joist jack can lift and support the subfloor while you work on it.

Always wear safety glasses and gloves when working with power tools and follow all manufacturer instructions.

Safety Precautions

Safety should always be your top priority when fixing high spots in your subfloor.

1. Wear Protective Gear

Always wear protective gear such as safety goggles, gloves, and a dust mask when working with power tools or chemicals. This will help protect you from flying debris, sharp edges, and harmful fumes.

2. Turn Off Power

Before working on your subfloor, turn off the power to any electrical outlets or appliances in the room. This will help prevent electrical shock or fire hazards.

3. Use Proper Tools

Make sure to use the right tools for the job. Using the wrong tool can cause damage to your subfloor or even result in injury.

For example, a circular saw should be used to cut plywood, while a reciprocating saw is better for cutting through nails and screws.

4. Check for Hazards

Before starting any work, check the area for any hazards, such as loose nails, screws, or debris. Clear the area of any hazards before starting work.

5. Work with a Partner

Working with a partner can make the job easier and safer. They can help support heavy tools or materials, hold a flashlight, or get help in an emergency.

Fixing High Spots: Sanding Method

If you have identified high spots in your subfloor, you can fix them using the sanding method.

This method involves sanding down the high spots until they are level with the rest of the subfloor. Here's a step-by-step guide to help you get started.

Rent or Buy a Floor Sander

You will need a floor sander to sand down the high spots. You can rent or buy a floor sander from your local hardware store. Make sure to choose a sander with coarse grit sandpaper.

Sand the High Spots

Start sanding the high spots with the floor sander. Move the sander back and forth over the high spots until they are level with the rest of the subfloor. While sanding, wear protective gear like a dust mask and safety glasses.

Check the Level

Once you have sanded down the high spots, recheck the subfloor level. Use a straightedge or level to ensure that the subfloor is level. If there are still high spots, repeat the sanding process until the subfloor is level.

Clean Up

After sanding, clean up the dust and debris from the subfloor. Use a vacuum cleaner or broom to remove all the dust and debris.

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Fixing High Spots: Planing Method

If you have high spots on your subfloor, you can use a planer to level them out. Planing is a simple process that involves removing material from the high spot until it's level with the rest of the subfloor.

Choose the Right Planer

Different planers are available, including handheld and electric ones. Electric planers are efficient but consider affordability and ease of use.

Set the Depth of the Planer

Set the planer's cut depth, ideally to a small amount, like 1/16 inch, to prevent excessive material removal.

Start Planing

Hold the planer securely and plane the high spot, ensuring not to create a low spot by over-planing.

Check Your Progress

After planing, use a straightedge or level to check for remaining gaps. Continue planing as necessary.

Sand the Planed Area

Sand the leveled area with fine-grit sandpaper to smooth any roughness without scratching the subfloor.

Clean Up

Sweep or vacuum sawdust and debris, and wipe the area with a damp cloth if needed.

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Fixing High Spots: Self-Leveling Compound Method

Clean the Subfloor

Ensure the subfloor is debris-free by sweeping and vacuuming thoroughly.

Apply the Self-Leveling Compound

Mix and apply the compound per the manufacturer's guidelines, ensuring it's level with the surrounding area.

Allow Compound to Dry

Let it dry as specified by the manufacturer, which may vary from hours to a day.

Sand the Surface

Post-drying, sand any rough spots to ensure a level and smooth surface.

Apply a Primer

Use a primer to enhance the adhesion of the new flooring, adhering to its specific instructions.

Install the New Flooring

After the primer dries, proceed with your new flooring installation.

Post Repair Steps

Once you have fixed the high spots in your subfloor, you should follow a few post-repair steps to ensure the subfloor is ready for the next stage of your project.


After fixing the high spots, you should sand the entire subfloor again to ensure it is level.


Once you have sanded the subfloor, you should clean the entire area to remove dust and debris.


If there are any gaps or holes in the subfloor, you should fill them with wood filler. Use a putty knife to apply the wood filler, and smooth it out so it is level with the rest of the subfloor.

Allow the wood filler to dry completely before sanding the area.


Before installing any flooring, you should prime the subfloor to ensure it is ready for the new flooring.

Use a primer designed explicitly for subfloors and apply it evenly to the entire subfloor. Allow the primer to dry completely before installing the new flooring.

Maintenance Tips

Maintaining your subfloor is crucial to prevent high spots from forming. Here are a few tips to keep your subfloor in good condition:

  • Regularly inspect your subfloor for any signs of damage or wear and tear.
  • Keep your subfloor clean and dry. Avoid allowing any water or moisture to sit on the subfloor for an extended period of time, as this can cause it to warp or rot.
  • Use the appropriate cleaning products when cleaning your subfloor.
  • Avoid placing heavy objects or furniture on the subfloor, as this can cause it to sag or warp over time.

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