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Gap Between Bathroom Vanity and Wall? How To Fill It Like a Pro

Taking on a complete bathroom renovation? Replacing a worn-out old vanity? The new vanity probably won’t be the exact same size as the old one. One of the biggest challenges is figuring out how to fill the gap between vanity and wall.

Whether you’re dealing with a slight space or something more substantial, we can help you figure out how to fill the gap between vanity and wall space.

Depending on the size of the gap, you can use several creative solutions. Common options include caulk, installing a backsplash, or inserting a filler strip.

Gap Between Bathroom Vanity and Wall

How To Avoid a Large Gap Between Vanity and Wall As Best as Possible

Start by shutting off the water and removing the old sink. Install your new vanity as close to the wall as possible to get a good idea about what size gap you need to fill.

If you have questions about removing your old vanity, this video is helpful. 

Follow These Steps To Install the Vanity:

  1. Measure the new vanity and measure the wall space.
  2. Make marks on the wall with a pencil or snap a chalk line.
  3. Line up the new vanity with the wall or floor to see how much gap exists. It’s best to line up with the wall so the final install is less noticeable and more secure.
  4. Ensure water pipe holes in the back of the cabinet match up with existing plumbing. If not, cut holes in the new vanity.
  5. Attach the new vanity to the wall. If the setup is floating, use shims to hold up the vanity so you can screw it in level. Be sure to use wall plugs or anchors to ensure a secure fit to the wall.
  6. Ensure pipes are free and not choked before connecting to the new sink and faucet.
  7. If the countertop and sink aren’t already connected, connect them with silicone and clips. Do not hook up the water lines until the sink is securely connected.
  8. Once the vanity is in place, reconnect the water lines and turn the water back on. Connect the hot and cold lines properly and be vigilant when checking for leaks. Use a flashlight and patience to look for any water drips (if your shower head drips after turning it off, read our solution here).
  9. Once the water is back on, and you are certain there are no leaks, then and only then can you proceed to fill any gaps between the vanity and wall.

Why Do I Need To Cover Gaps?

It might seem a little silly to worry about a gap between a bathroom vanity and the wall. If you’re like me, you wonder why it even matters if everything works just fine with the gap.

Certainly, covering any gaps makes the vanity look finished, but that’s not the only reason. Not only does the vanity look more admirable and aesthetically pleasing, but it is also healthier for you and your family.

Damp, dark places are the breeding ground for mold. Bathrooms are notorious for being the perfect environment for mold to grow. As you know, mold can make you quite sick. Preventing mold growth is better than dealing with remediation costs and potential health issues.

Filling gaps between the vanity and wall keeps the water from splashing out from the sink. You don’t have to worry about it hitting the wall and rolling down into the pits of darkness. 

How To Fill the Gap Between Bathroom Vanity and Wall

Whether the back or side wall has a gap, particular methods can be used to seal the opening, so the vanity appears flush with the wall.

Use a Backsplash

Use a Backsplash

Picking a backsplash that matches the sink is the easiest way to hide any gaps. Backsplashes can come in a variety of thicknesses. 

Most natural stone backsplashes are around 3/8 to 1/2 inches thick. Standard sizes are usually enough to cover any gap without causing an additional gap elsewhere. 

Make sure that you use a matching color silicone to give it a seamless look.


Caulk is a beautiful tool to have in the house at any given time since it is an excellent, fast-drying sealant. Plus, caulk has come a long way over the years. 

Today we have access to many caulk colors so you don’t have to stick with white. It is less stinky than before with low-odor options.

Using a ribbon to fill the gap between the wall and the vanity forms a tight seal. It prevents water, debris, and mold from getting behind the vanity.

Use a Backer Rod

A backer rod is a flexible foam-like rod that is great for joints and filling significant gaps. To install a backer rod, follow these steps:

  • Cut the rod to size.
  • Stuff it lightly into the void
  • Use caulk or silicone to keep the rod in place and cause an eye-pleasing aesthetic. 

A backer rod works great in expansion and retraction situations, like bathroom. The caulk or silicone won’t crack or break the seal.

Bathroom Sealant Tape

Sealant tape is a unique product that is easy to use. It comes on a roll that you can pull off like tape but seals like caulk. 

If you don’t like working with caulk because it’s too messy, sealant tape might work. It fills small gaps between the countertop and wall. 

Since it works like regular tape, this sealant is easy to square off. That means a neater finished product. However, it must be a smaller gap since the tape can puncture easily if the gap is too large.

Vanity Filler Strip

Vanity filler strips are pre-cut wood, stone, or vinyl pieces that can fit and overlap the gap

Filler strips are an attractive option to add as a frame for your picturesque new vanity. Strips can connect by silicone or by being tacked in, depending on where it’s being fastened. 

Note that you must use caulk or silicone with the filler strips. Sealing the strips at the connection points prevents water from seeping in and weakening the joints. 

Metal Strip Trim

Metal Strips are another convenient way to quickly frame the vanity and the wall. 

These strips are usually angled slightly to allow run-off water to hit the bevel and puddle instead of seeping behind the vanity. It works a lot like wood or vinyl filler strips. 

Metal strips were more popular years ago, whereas stone and other materials are much more readily available today.

Tile the Wall

If the gap between the wall and sink is small, installing tile as a backsplash can flawlessly cover that gap. Using grout and a bead of caulk will seal any chances of water creeping in and running down the wall. 

Tile is usually between six to ten millimeters thick, but there is no standard size for tile thickness. Therefore, you’ll want to measure the tile you select before installing it as a backsplash.

How Much Gap Is Acceptable?

Getting your gap less than ½ inch wide is the goal. Having a large gap that cannot be filled with traditional fillers is unacceptable. Most fillers can cover gaps that are under one inch thick. If you use a tile and still have a slight gap, caulk can fill the remainder of the opening.

You can also choose a free-standing vanity that requires at least a four-inch gap between the wall and vanity, so it is possible to clean up any spills from behind the vanity to avoid any future mold growth.

How Much Gap Is Acceptable

Related Questions

Here are some related questions when filling gaps between the countertop and wall when installing a new vanity.

How much of a gap can you safely caulk?

You can safely caulk a gap that is about a ¼ inch without worrying that it will sink or break the seal. 

When trying to caulk more significant gaps, gravity can pull the caulk down instead of staying in a long ribbon. If you need to caulk a larger opening, packing the gap with a backer rod, shims, or other pro-grade packing material could help maintain a solid seal on the caulk.

What is the difference between caulk and silicone?

Elasticity is the difference between caulk and silicone. Since both are sealants, either can be used when filling a gap. However, silicone is more flexible to withstand slight movements in expansion and contraction. Nevertheless, silicone takes longer to dry and set.

Can I use clear silicone to fill gaps?

You can use clear silicone to fill gaps, but it won’t look seamless. It’s because clear silicone dries clear or milky, leaving the appearance of the gap still visible. 

For a seamless look, it’s best to use a colored silicone or caulk that will match one or both areas you are sealing. For example, use white silicone to match a white sink butted to a blue wall.


When using the right resources, filling a gap between the vanity and wall can be reasonably simple. Remember to use materials that will make the gap disappear. 

Not all walls are created square, so use a filler that will allow the most seamless appearance when filling the gap. Using a suitable filler will not only make the vanity project look finished but will prevent mold from growing behind the vanity in the future.

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