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Bathtub Creaking When You Step In? The Support Foam Fix

A creaking tub has a gap under its floor that lets it flex. Find the spot, then fill the space with low-expansion foam so it stops moving.

By Jamilur Rahman Updated November 5, 2026 · 6 min read

Time
1 hour plus cure time
Cost
Under $20
Difficulty
Medium
An empty white acrylic bathtub with a faint shadow gap along its lower edge where it meets the bathroom floor
In this guide
  1. Quick answer
  2. Free vs. permanent fix
  3. What you'll need
  4. Why it happens
  5. Try this first (free)
  6. When free fixes aren't enough
  7. Buy the fix
  8. What is under your tub? The material matters
  9. What to skip
  10. FAQ
  11. Related problems

Quick answer

Why is my bathtub creaking when I walk in it? Usually there is a gap between the bottom of the tub and the floor, so the tub flexes under your weight. Find where it moves, then fill the gap with low-expansion polyurethane foam from a can, which stops the flex and the creak.

Free fix vs. permanent fix

Free fix · 30 minutes

Find the spot and shim the gap

  • Step around the tub floor to find where it flexes
  • Look for an access panel, basement or crawlspace below
  • Tap wood shims into any gap you can see
  • Check that the tub rim is fastened to the wall studs

How long it lasts: A few months to years if the gap is small and visible. Shims cannot reach a gap you cannot see.

Most readers choose Permanent fix
Low-expansion polyurethane foam (illustration)
Illustration

Low-expansion support foam

The creak comes from the tub's thin floor flexing over an air gap. Low-expansion foam fills the space under the tub and cures into a firm support, so the floor stops moving. Use low-expansion foam only, since regular foam can push an acrylic tub out of shape.

What to get: Low-expansion polyurethane foam

How long it lasts: Years. Cured foam fills the whole gap and stays put.

Check price on Amazon

As an Amazon Associate I earn from qualifying purchases.

What you'll need

  • A helper

    One person steps in the tub while the other watches below

    Free

  • Flashlight

    To see the gap and any pipes or wires

    You have it

  • Gloves and safety glasses

    Foam sticks to skin and is hard to remove

    You have it
  • Wood shims (illustration)
    Illustration

    Wood shims

    A cheap fix for a small visible gap

    Check price
  • Our pick
    Low-expansion polyurethane foam (illustration)
    Illustration

    Low-expansion polyurethane foam

    Labeled minimal-expanding or window and door foam

    Check price

Why it happens

1

A gap under the tub floor

Acrylic and fiberglass tubs have thin floors that need solid support. A gap between the tub and the subfloor lets the floor flex and creak under your weight.

2

A support bed that shrank

The mortar or foam bed some tubs sit in can shrink or crack. When the support pulls away, the tub moves.

3

A loose rim or wall flange

The tub's rim is usually fastened to the wall studs. If those fixings loosen, the tub shifts at the edge.

4

A squeaky subfloor

Sometimes the noise is not the tub at all. Boards or nails in the subfloor rub, and the tub carries the sound.

Try this first (free)

Do these in order, starting with the simplest.

  1. Locate the creak

    Tool used: A helper

    Step in at different spots while a helper listens and watches from under the tub or at an access panel. Note where it moves or makes noise, and mark that spot with tape.

  2. Check the rim and the wall edge

    Tool used: Flashlight

    Look along the tub rim where it meets the wall. If you can see loose screws, snug them gently. Do not crack the tub, and reseal any gap with caulk afterward.

  3. Look under the tub

    Tool used: Flashlight

    Open any access panel, usually behind the faucet wall, in a closet or room next door, or from a basement ceiling. With the flashlight, look for the gap between the tub bottom and the floor. Take care around pipes and wires.

  4. Shim what you can see

    Tool used: Wood shims

    Tap wood shims into the gap at the spot that flexes, snug but without lifting the tub. They work for visible gaps but cannot reach under the whole tub.

    Wood shims (illustration)
    Illustration

    Tool for this step

    Wood shims · A cheap fix for a small visible gap

    Check price on Amazon

  5. Fill the gap with foam

    Tool used: Low-expansion polyurethane foam

    Wear gloves and glasses, shake the can, and spray a thin, steady layer into the gap. Foam still expands, so work in short bursts. Add more after a few minutes if needed, and keep weight off the tub for the cure time on the can.

    Low-expansion polyurethane foam (illustration)
    Illustration

    Tool for this step

    Low-expansion polyurethane foam · Labeled minimal-expanding or window and door foam

    Check price on Amazon

When free fixes aren't enough

Shims only handle a gap you can see and reach. Most tubs hide the gap, and the tub floor is thin, so foam is what fills it. Stop and call a pro if the floor beside the tub is soft or stained, if you see a leak, or if you cannot reach the underside without cutting into a wall or floor. A creak plus water damage is a plumbing or rot problem, not a foam job.

Buy the fix

Still stuck after the free fixes? These are the products we would look at.

Our picks compared
PickProductFixesWho it's forBuy
Best pick
Low-expansion polyurethane foam (illustration)
Illustration
Low-expansion polyurethane foam
a flexing tub floor over a gap you can reach Anyone with an acrylic or fiberglass tub that creaks and a way to reach the underside. Check price
Budget pick
Wood shims (illustration)
Illustration
Wood shims
a small, visible gap that makes the tub flex People who can see and reach the gap from an access panel. Check price
Best pick
Low-expansion polyurethane foam (illustration)
Illustration

Low-expansion polyurethane foam

Fixes: a flexing tub floor over a gap you can reach

Look for: Labeled low-expansion, minimal-expanding, or window and door foam; Cures firm, not soft or crumbly; Comes with a straw nozzle you can aim into a gap.

Who it's for
Anyone with an acrylic or fiberglass tub that creaks and a way to reach the underside.
Honest downside
You cannot reach the underside, or the tub is cast iron with its own feet. Ask a pro.
Check price on Amazon
Budget pick
Wood shims (illustration)
Illustration

Wood shims

Fixes: a small, visible gap that makes the tub flex

Look for: Tapered shims thin enough for a narrow gap; Dry, untreated wood; A set with several sizes.

Who it's for
People who can see and reach the gap from an access panel.
Honest downside
You cannot reach the gap, or the shims will not stay in place. They can slip out.
Check price on Amazon

As an Amazon Associate I earn from qualifying purchases. We don't show prices because they change, so use the button to see today's price.

How we picked: How we picked: this page is based on bathtub installation and support guides, the instructions printed on low-expansion foam cans, and the problems and fixes people report in reviews. We do not test products by hand.

What is under your tub? The material matters

  • Acrylic or fiberglass: a thin shell that needs full support from below, such as foam or a mortar bed. Foam is the fix on this page.
  • Enameled steel: it can pop or creak where it meets the floor. Shim and foam carefully.
  • Cast iron: very heavy and held up by its own feet or base. A creak usually comes from the floor, not the tub, so call a pro.

What to skip

Regular expanding foam and caulk

High-expansion foam grows with a lot of force and can push the tub up, bow its floor or crack it. Caulk only seals the edge and does nothing for a flexing floor. Use foam labeled low-expansion.

Frequently asked questions

Why does my tub creak even though it looks solid?
The tub's floor is thin and needs support under it. Any gap lets it flex a hair, which shows up as a creak even when you cannot see movement.
Is support foam safe for an acrylic tub?
Yes, if you use low-expansion foam in short bursts. Regular expanding foam can warp the tub. Follow the instructions on the can and let it cure.
How do I get under the tub?
Look for an access panel behind the faucet wall, in a closet or room next door, or from a basement or crawlspace below. If there is none, call a pro rather than cutting into a wall.
Can a creaking tub cause damage?
A tub that flexes can crack, and cracks let water into the floor. Fix it soon. If the floor beside it feels soft, have a pro look at it.

As an Amazon Associate I earn from qualifying purchases. Affiliate disclosure

Low-expansion polyurethane foam (illustration)
Illustration

Our pick: Low-expansion polyurethane foam

Check price