How to Seal a Gap Between the Baseboard or Wall and the Floor

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Seal out dust, moisture, and pests by filling the gap

Co-authored by Art Fricke and Cheyenne Main

Last Updated: May 21, 2024 Fact Checked

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• Cleaning & Prepping the Area
|
• Choosing the Right Caulk
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• Caulking the Gap
|
• Identifying Foundation Issues
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• Expert Q&A
|
• Tips
|
• Things You'll Need

|Show more |Show less

Temperature fluctuations, a sagging subfloor, or missing baseboards can create gaps between a wall and the floor beneath it—luckily, caulk can fill most small gaps. Fill large gaps with spray foam insulation, scrap wood, or a long piece of foam insulation. Then, all you need to do is install a baseboard and caulk around it. We talked to commercial handyman Kevin Turner as well as home renovation and repair specialist Art Fricke to find the best way to fill gaps with caulk. If the gap is a sign of a deeper structural problem, we have advice for how to identify and fix that, too. Keep reading to learn more!

Fixing a Large Gap Between the Wall and Floor

If the gap is smaller than ¹⁄₂ in (1.3 cm), fill it with silicone caulk. Fill gaps larger than ¹⁄₂ in (1.3 cm) with a few pieces of wood, foam insulation, or spray insulation. Nail a baseboard or quarter round over the filled gap, then caulk around the baseboard.

Steps

Section 1 of 4:

Cleaning & Prepping the Area

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1. 1
   Scrape off any old caulk from the gap, if necessary. If there’s any old or cracked caulk along the gap, take a utility knife or a putty knife and run the edge along it to scrape it off. Be careful not to strip or chip the paint on the walls. Continue scraping until all of the old caulk is removed.

   • If there are gaps in your wooden floor, Turner says to “use a pry bar or a flooring tool to pull it together.”
   • Turner says you can also use “a little bit of wood filler, and then get one of those furniture marking pens that best color matches your floor and color it to match.”

   Tip: Use 180-grit sandpaper to scrub off any stubborn bits of caulk.
2. 2
   Vacuum any dust and dirt from the inside of the gap. Use the hose extension on a vacuum cleaner and insert the tip into the gap. Vacuum all along the gap to suck up any dust, dirt, debris, and pieces of caulk that may be there. Dirt and other contaminants can affect how well you seal the gap, so work the hose attachment around the area to remove as much as you can.

   • If you don’t have a vacuum or a hose attachment, use a damp cloth to scrub dirt and debris out of the gap.
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3. 3
   Scrub the gap with rubbing alcohol to sanitize it. Fill a bowl with rubbing alcohol, dip a clean sponge or cloth into it, and wring out the excess. Scrub the top and bottom of the gap to kill germs, remove any loose debris, dirt, and stains, and sanitize the area so mold doesn’t form when you seal it.

   • If you don’t have rubbing alcohol or your floor is wood, marble, painted, or granite, mix 1 US gal (3.8 L) water and 1 US tbsp (15 mL) bleach as an alternative cleaning solution.
   • Rubbing alcohol can irritate your eyes and sinuses if you breathe in the fumes directly. Consider wearing a mask and goggles and work in a well-ventilated area.
4. 4
   Let the area around the gap dry completely. Run a clean, dry cloth over the area and wait a few hours for it to air dry. To speed up the drying process, aim a blow dryer set on low heat to dry the wall and floor near the gap. Touch the area with your finger to make sure it’s completely dry so moisture doesn’t get trapped in the caulk.

   • Moisture can cause bacteria and mold to develop in the wall.
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Section 2 of 4:

Choosing & Preparing the Caulk

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1. 1
   Use silicone caulk to waterproof kitchens and bathrooms. If you’re fixing a gap between a tile floor and wall, such as in a shower or a bathroom, go with a silicone caulk so you can create an airtight, waterproof seal. Fricke recommends buying “silicone caulk that's 100% silicone, fast cure, [and] water ready in 30 minutes.”

   • If the gap is larger than ¹⁄₂ in (1.3 cm), insert a few pieces of wood, a strip of foam insulation, or spray insulation into the gap.
   • Silicone caulk is generally clear in color. The waterproof seal will help prevent moisture from getting into your walls, which can lead to rot and mold.
   • Fricke says that silicone caulk cures through crystallization as it's exposed to oxygen.
2. 2
   Choose latex caulk for gaps in non-humid areas of the house. If you’re fixing a gap between a floor and a painted wall that isn’t exposed to a lot of humidity, such as a bedroom or living room wall, use a latex caulk. Latex dries quickly and expands slightly to fill cracks. Choose a color that closely resembles the paint of your wall so the gap isn’t noticeable.

   • Latex caulk will create a tight seal but isn’t as waterproof as silicone.
   • Fricke says that latex caulks cure through an evaporation process.
3. 3
   Press the release trigger and pull back the rod on the caulk gun. Find the small metal trigger on the back of the handle of the caulk gun. Press the trigger and hold it down to release the steel rod. Then, pull the steel rod all the way back and release the trigger.

   • You may need to twist the steel rod to lock it into place.
4. 4
   Insert the caulk tube into the caulk gun with the nozzle facing away. Place the base of the caulk tube in the caulk gun so it’s flush against the back. Then, rest the nozzle end into position at the front of the gun. Push the metal rod back into place so it’s pressing against the back of the caulk tube to hold it securely.

   • Shake the caulk gun gently to make sure the caulk tube is secure.
5. 5
   Cut the caulk tube to make an opening the size of your gap. Insert the sealed nozzle into the gap until it can’t go any further to find the width that the nozzle opening needs to be to fill it. Take a pair of scissors or a utility knife and cut the nozzle at a 45-degree angle where it made contact with both the wall and floor so it’s the size of the gap.

   • Cutting the nozzle at an angle helps you guide the caulk into the gap as it flows out of the tube.
6. 6
   Push a long nail into the nozzle to pierce the seal. Stick a long nail or metal rod into the nozzle end of the caulk gun and push it through the internal seal. Keep the nozzle held upright and remove the nail or rod from the nozzle.

   • You could also use a long pin or piece of wire to penetrate the internal seal.
   • Some caulk guns have a metal rod you can use to pierce the internal seal of the caulk tube.
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Section 3 of 4:

Caulking the Gap Between the Floor and the Wall

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1. 1
   Insert the tip of the caulk tube into the gap at a 45-degree angle. Hold the caulk gun near the gap and tilt it so it’s angled to keep the caulk from falling straight out of the nozzle when you squeeze the trigger. Stick the tip of the nozzle into the gap so it’s flush and even with it.

   • Instead of trying to use a caulking tool to make a straight line, Fricke says to outline the gap along with wall with masking tape instead.
   • If the gap is larger than ¹⁄₂ in (1.3 cm), measure the length of your walls and cut baseboards or quarter rounds to size. Nail them over the cracks under each wall.
   • If you’re able to insert the tip of the nozzle more than ¹⁄₄ in (0.64 cm) deep, then cut the nozzle again so the opening is wider.
2. 2
   Pull the trigger on the caulk gun to push the caulk out of the nozzle. Once the nozzle is in position, gently pull the trigger on the caulk gun to force the caulk out of the tube and into the nozzle. Continue tapping on the trigger until the caulk starts to flow out of the tip of the nozzle.

   • If the gap is larger than ¹⁄₂ in (1.3 cm), caulk a thin line across the bottom and top of each baseboard to seal the gap.
   • Try not to hold the trigger down or too much caulk may flow out of the nozzle.
3. 3
   Move the tube down the gap to fill it with caulk. As the caulk starts to flow out of the nozzle, keep lightly tapping on the trigger to keep the flow steady and consistent. Move the nozzle down the entire length of the gap to fill it with the caulk.

   • For bigger gaps, move slowly and allow more caulk to flow into the area underneath the wall.

   Tip: If too much caulk does flow out of the nozzle, immediately wipe it up with a clean cloth so it doesn’t have a chance to set.
4. 4
   Use a caulking tool or damp cloth to smooth the caulk in the gap. A caulking tool is made of plastic or metal with straight corners and edges used to smooth the caulk to form an even layer. Run a caulking tool (or your finger covered in a damp rag) over the caulk to remove any excess and form the caulk into a smooth and even layer.

   • A smooth layer of caulk will create a tighter and better seal.
   • You can find caulking tools at home improvement stores, hardware stores, and online.
5. 5
   Allow the caulk to dry for 24 hours. Leave the gap undisturbed for a full day so the caulk can dry and set to form a tight seal. If you fix a gap in a bathroom or shower, avoid using the shower for a full day so the moisture won’t damage the caulk. Lightly touch the caulk with your fingers after 24 hours to make sure it’s dry.

   • According to Fricke, you can speed up the drying process by turning a fan on or using a blow dryer set on low heat. If you use heat, “that's actually going to make it take longer to cure.”
   • If the caulk still isn’t dry, wait another 12 hours.
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Section 4 of 4:

Identifying Potential Foundation Issues

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1. 1
   Look for sloped or uneven floors for signs of foundation settlement. Check the floor near the gap and look to see if it’s sloped or uneven. Sloped floors are a sign that the building’s foundation is settling and the structure is uneven. If your floors are uneven, contact a licensed building inspector to check the foundation and offer potential solutions.

   • Other signs of uneven foundation settling include cracked walls or windows, visible cracks in the foundation, or windows and doors that don’t open or close easily.
   • Look online for building inspectors in your area. The inspector may tell you that you need to hire a contractor to repair your foundation.
   • Problems with the foundation could lead to serious structural damage if they're not repaired.
2. 2
   Check the floor joists in your crawl space for moisture damage or rot. Locate the building’s crawlspace and look to see if there are wooden floor joists beneath the walls of the structure. If there are, look for cracks, splinters, and signs that the wood is damaged or rotting. Contact a building inspector to view the joists if you believe that they are damaged.

   • Damaged floor joists can cause the floor to move, which can create a gap between the floor and the wall above it.
   • Look online for a building inspector you can hire to check your floor joists if you find signs of damage.
3. 3
   Examine your walls for tiny pin holes caused by termites. Termites can eat through the support structures of your home, causing the house to settle and create gaps between the floors and walls. Look for small holes, mud tubes, or rattling or rustling sounds in your walls. Contact a licensed exterminator as soon as possible to take care of the problem.

   • Other signs of termites include discolored or drooping drywall, peeling paint, buckling floorboards, and crumbling or damaged wood.
   • Call a local exterminator to investigate your home if you believe you have a termite infestation.
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Expert Q&A

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• Question

  How can I fill in gaps between floor boards?

  

  Kevin Turner
  Commercial Handyman

  Kevin Turner is a handyman and the owner of Red Gator Maintenance, a handyman business based in Fresno, California. Working on handyman-related projects since the age of 12, Kevin specializes in a wide variety of home improvement projects such as (but not limited to) lighting/electrical, plumbing, deck staining, drywall repairs, cabinet installation, air conditioning, trash removal, and window, roof, and appliance repairs.

  

  Kevin Turner

  Commercial Handyman

  Expert Answer

  You can use a pry bar or flooring tool to try and pull the boards together. If that doesn't work or you don't want to risk damaging the boards, you can use wood filler to fill in the gap. Then, just use a furniture marking pen to try and match the color of the wood filler to the color of your floor.

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• Question

  Can I use caulk to fill the gaps between floorboards?

  

  Kevin Turner
  Commercial Handyman

  Kevin Turner is a handyman and the owner of Red Gator Maintenance, a handyman business based in Fresno, California. Working on handyman-related projects since the age of 12, Kevin specializes in a wide variety of home improvement projects such as (but not limited to) lighting/electrical, plumbing, deck staining, drywall repairs, cabinet installation, air conditioning, trash removal, and window, roof, and appliance repairs.

  

  Kevin Turner

  Commercial Handyman

  Expert Answer

  You can, but wood filler is probably a better option. If you go for caulk, look for brown or tan caulk that will closely resemble the color of your floor.

  Thanks! We're glad this was helpful.
  Thank you for your feedback.
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• Question

  Why do floor boards spread apart?

  

  Kevin Turner
  Commercial Handyman

  Kevin Turner is a handyman and the owner of Red Gator Maintenance, a handyman business based in Fresno, California. Working on handyman-related projects since the age of 12, Kevin specializes in a wide variety of home improvement projects such as (but not limited to) lighting/electrical, plumbing, deck staining, drywall repairs, cabinet installation, air conditioning, trash removal, and window, roof, and appliance repairs.

  

  Kevin Turner

  Commercial Handyman

  Expert Answer

  Weather and changes in temperature can cause the wood to expand and contract. Over time, this can lead to gaps in the floor boards.

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  Thank you for your feedback.
  If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow

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Tips

• Homeowner’s insurance typically does not cover damage from a shifting or settling foundation. You can get earthquake or flood policies to cover foundation damage from those events.
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• Some homeowners see caulking baseboards as a waste of money because the caulk wears over time. However, caulking can save your floor from moisture damage and keep bugs out.
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Things You’ll Need

• A few pieces of wood, a strip of foam insulation, or spray insulation (for large gaps)
• Caulk
• Caulk gun
• Caulking tool
• Baseboards
• Vacuum
• Rubbing alcohol
• Utility knife or putty knife