Short answer
A gap opening between the tub and the wall is almost always a failed caulk joint, and a new bead closes it. Press the caulk and then step into the empty tub and watch the gap. If the gap stays the same width, the joint gets cut out, cleaned and re-sealed, and the wall and tub stay where they are. If the gap opens as you stand in it, the tub is not supported properly underneath, and it gets shimmed and re-secured before any new caulk goes on, because caulk on a tub that moves splits again within months.
Tell a failed caulk joint from a tub that is not supported
- Look along the whole joint in strong light. A crack that runs the full length, with old caulk curling away, is a failed seal.
- Press the caulk with a fingernail. Caulk that is hard, cracked or peeling off in strips has lost its grip and cannot be patched.
- Step into the empty tub next to that wall and watch the gap. A gap that opens wider as you stand in it means the tub itself is moving.
- Press the tub floor with your foot in several spots. Firm everywhere is normal. Soft or springy means the tub sits on no support or on a rotted base.
- Check the floor at the base of the tub and the ceiling in the room below for stains, soft spots or a musty smell.
- Run the shower for 10 minutes, then look along that wall and inside the gap for fresh water.
If the gap stays the same width when you stand in the tub, and nothing below is stained, the joint is the whole problem and new caulk is the fix. If the gap opens as you step in, or the tub floor gives, stop and have the tub re-secured first.
Repair or replace
| Situation | What to do |
|---|---|
| Caulk cracked or peeling, tub does not move | Repair. Cut the old caulk out, dry the joint, and run new flexible mold-resistant caulk. |
| Gap opens when you stand in the tub | Repair. A pro shims and re-secures the tub rim to the framing, then re-caulks the joint. |
| Acrylic or fiberglass tub that flexes a little underfoot | Repair. Some flex is normal in a plastic tub. Re-secure the rim and use flexible caulk, not grout. |
| Tub floor feels soft or springy | Hire this out. The tub has lost its support or the base under it is rotted, and caulk hides that fault instead of fixing it. |
| Caulk black with mold, floor or ceiling below stained | Open and dry the wet area first. The joint has been leaking long enough to reach the structure. |
| Tub is cracked, or the wall panels move and feel wet | Replace the surround. Water is behind it, and sealing the front face traps it. |
What it costs
Runhome contractor estimates for this job, including the trip and assessment.
| Option | Range |
|---|---|
| Re-secure the tub rim and replace the caulk | $205 to $420 |
Can I do it myself?
Yes, if the tub does not move when you stand in it. Cut the old caulk out with a plastic scraper and a utility blade, scrub the joint with a bathroom cleaner, and let it dry for a day. Then run one bead of flexible mold-resistant caulk, with the tub full of water so the joint sets at its widest.
Hire someone if the gap opens when you step in, if the tub floor feels soft, if the wall panels move when you push them, or if the ceiling below is stained. Those faults are behind the wall, and new caulk over them buys a few months and costs you the floor.
What a contractor will ask you
Have these ready and you skip the back-and-forth.
- A wide photo of the whole tub and both walls, including the floor right below the gap.
- When you first noticed the gap, and whether it is getting wider.
- Whether any water has reached the bathroom floor or the ceiling below.
- How old the tub and the surround are.
- What the tub is made of. Acrylic and fiberglass flex under hand pressure, cast iron and steel do not.
- Whether the tub rim or floor moves when you step in near that wall.
- Whether the old caulk is moldy, cracked or peeling, and roughly when it was last done.
Common questions
- My bathtub is separating from the wall, is that serious?
It is urgent but usually cheap. An open joint sends shower water straight into the wall and the floor framing, and that damage costs far more than the caulk. Get it sealed within a few weeks, sooner if you see water on the floor.
- Can I just caulk over the old caulk?
No. New caulk does not bond to old caulk, and the bead peels away in a month. All of the old material comes out first.
- Why does the caulk around my tub keep cracking?
The tub is moving more than the caulk can stretch. That happens when the rim was never fastened to the framing, when the tub sits on no mortar bed, or when grout was used in the joint instead of caulk.
- The gap is wider than a caulk bead, what fills it?
Foam backer rod goes in first, then caulk over it. A joint over about 1/4 inch that is filled with caulk alone sags and splits.
- Does the tub have to come out to fix this?
Rarely. The rim is re-secured through the surround or from an access panel, and the tub stays. A tub only comes out when it is cracked or the framing under it is rotted.