Almost as important as buying a new bathtub is understanding how to maintain it. The first step in maintaining any bathtub is knowing which sealing agent belongs in which joint, because the wrong one fails in months and takes the wall behind it along for the ride.
The short answer: for the joint between a bathtub and the wall or floor, use 100 percent silicone sealant in a kitchen and bath grade, and look for a mildew resistance claim on the tube. Caulk is the broader family of sealing agents. Sealant is the silicone branch of that family, and the tub joint is one of the few places where the distinction genuinely decides whether the seal holds.
Below is what separates the two, which one each joint in your bathroom actually needs, and the application step that most people skip.
What are the main differences between caulk and sealant
In general, caulk and sealant are more or less interchangeable terms, because they refer to the same group of sealing agents applied the same way, through a caulking gun. Sealants are classified as caulk, and the main difference between the two is the material used.
Sealants are made from a flexible material, usually silicone, and stay flexible for their whole service life. Caulk is the umbrella term, covering sealing agents made from silicone, latex, acrylic or a blend of them. So every sealant is a caulk, but not every caulk is a sealant, and the ones that are not tend to dry hard.
That flexibility is the whole argument. A bathtub is not a fixed object. Fill it and it sinks slightly on its supports, drain it and it rises again. A material that stays elastic moves with that cycle. A material that dries rigid cracks along the same line every time.
One thing you will read that is not true
You will often see caulk described as the outdoor product and sealant as the indoor one. It is a tidy distinction and it does not survive contact with a hardware aisle. Silicone sealant is a mainstay of exterior weatherproofing, and GE sells its Advanced Silicone 2 line in a dedicated Window and Door variant rated for rain exposure. Acrylic latex caulk, meanwhile, is the standard interior material for trim, skirting and paint preparation.
Ignore indoors and outdoors. The useful questions are whether the joint gets wet, whether it moves, and whether it needs paint on it.
What is caulk
Caulk is an umbrella term for a range of sealing agents made from silicone, latex, acrylic or a combination. It is applied with a caulking gun to seal gaps, repair cracks or join surfaces. Its advantages are that it is easy to apply, easy to remove, and, in its acrylic latex forms, that it can be painted over for a seamless finish.
The catch is that the acrylic latex versions were never designed to sit in standing water. They give up water to the air to harden, and once hard they have very little give. In a joint that flexes under a few hundred pounds of water and bather, that is the wrong property.
Pros and cons of caulk
This table covers acrylic latex and siliconized acrylic caulk, which is what people mean when they say caulk rather than sealant.
| Pros | Cons |
|---|---|
| Takes paint, so it disappears into trim and painted walls | Breaks down under standing water |
| Tools smooth with a wet finger and cleans up with water | Dries rigid, so it splits in a joint that moves |
| Low odour and easy to work with in a small room | Shorter service life in a wet area |
| Easier to cut out and replace | Not the right choice for the tub joint itself |
What is sealant
Sealant is a type of caulk, typically made from a flexible material, usually silicone. Its advantage over rigid caulk is flexibility, which lets it fill awkward or intrusive angles while still holding a strong bond. Where caulk hardens and becomes rigid as it dries, silicone does not, which makes it the stronger material for resisting water and mildew.
There are two main types you will meet:
- Polyurethane sealant. Used on roofs, rain gutters, joints between prefabricated building elements, and rainwater collection pipes.
- 100 percent silicone sealant. Used for bathtub and shower surrounds, doors and drains. This is the one your tub wants.
Pros and cons of sealant
| Pros | Cons |
|---|---|
| More water resistant than standard caulk | Harder to apply and remove than caulk |
| Flexibility allows for versatile applications | Strong odour while curing |
| Holds up to repeated temperature swings | Cannot be painted over |
| Resists mildew better in a wet joint | Needs a clean, fully stripped surface to bond |
What to look for on the tube
This is where most bathroom sealing goes wrong, and it goes wrong in the shop rather than at the joint. Three things on the front label decide whether you bought the right product.
- The words 100 percent silicone. Not siliconized. Not silicone enhanced. Not plus silicone. Those phrases describe acrylic latex with a modest amount of silicone added, and they sit in a different performance class entirely. If the tube needs an adjective in front of silicone, it is not 100 percent silicone.
- A kitchen and bath or tub and tile designation. This tells you the formula is intended for continuous moisture rather than occasional splashing.
- A mildew resistance claim. Mildew resistant formulas carry additives that slow the black staining that makes people redo a joint long before it has actually failed.
Colour is worth a thought too. Clear silicone hides an imperfect bead better than white does, and on a dark floor or a stone surround it disappears. White reads cleaner against white tile, and shows mildew sooner, which is arguably a feature.
Which one does your joint actually need
Four questions. The answer changes with the joint, not just the room.
How do you know which to use for a bathtub and showers
In general, sealant is the preferred sealing solution for bathtubs and showers, because it is more water resistant than traditional caulk. Silicone sealant forms a watertight seal that survives heavy temperature changes.
You can also use a hybrid acrylic latex silicone caulk, which offers some of both: more resilience than plain acrylic latex, and the ability to take paint. It is a reasonable compromise for the trim around a bathroom, and it is still not what belongs in the tub joint. When the choice is between a bead you can paint and a bead that will not let water through, the tub joint always wants the second one.
The substrate matters as well. A stone resin tub, an acrylic one and a cast iron one all move differently under load, and cast iron on a timber floor moves the most, simply because it is heavier. If you are still choosing, our guide to common bathtub materials covers how each behaves once it is installed.
When to use each one
When to use caulk
Caulk is used mostly to close gaps between walls and woodwork, but it also works for railings, molding, or blending mitered corners. It performs well on cornices, coving, architrave and skirting. In a bathroom, think of it as the material for everything that is near the water rather than in it.
When to use sealant
Sealant is the right choice wherever you need to seal a bath, a shower, or any similar area where movement occurs. It also suits kitchen and bathroom sinks, the base of a toilet, and the bottom edges of a bath.
Browsing the sealant aisle you will also find exterior silicones, sold for door frames, windows and cracks in brickwork. They are the same chemistry aimed at weather rather than steam, which is the clearest sign that the indoor and outdoor split is not a real rule.
What they actually do in a bathroom
For installing a bathtub and repairing a bathroom, both are genuinely useful. They act as a light adhesive and a water seal at once. The jobs worth knowing about:
- Sealing cracks and gaps, including the hairline splits covered in our guide to bathtub cracks
- Creating a watertight seal where the tub meets the wall and the floor
- Forming a solid, sealed base between the bathroom walls and the tub
- Bedding a drain flange so water cannot track around it
- Sealing seams at trim, which we cover in more detail in what a bathtub trim is
- Refreshing tired tile surfaces where the perimeter joint has gone
What a bead cannot do is waterproof a bathroom. It seals a line, not a surface. Everything behind the tile does that job, and if that layer is missing or damaged then no amount of silicone at the edge will save it. Our guide to waterproofing a bathroom properly covers what sits behind the finish.
How to seal a tub joint, step by step
This is the part most guides skim, and it is the part that decides the outcome. Nine steps, in order.
1. Strip out every trace of the old bead
Fresh silicone will not bond to cured silicone. Not partially, not weakly, not at all. A new bead laid over an old one is stuck to a film that is itself letting go, which is why a joint that has been recaulked three times fails faster each time.
Cut both edges with a utility knife or a dedicated caulk removal tool, then pull the bead out in one length if you can. Scrape the residue with a plastic putty knife rather than a metal one, especially on stone resin or acrylic, where a steel edge leaves scratches that show.
2. Kill the mildew before you cover it
Any black staining left in the joint keeps growing under the new bead and shows through within weeks. Clean the bare joint, let the mildew treatment do its work, then rinse.
3. Get the joint completely dry
Silicone needs a dry, clean, oil-free surface. Wipe the joint with rubbing alcohol as a final pass, which lifts soap residue and body oils that water alone leaves behind, and let it flash off. Run the extractor fan.
4. Fill the tub with water
This is the step almost nobody mentions and the one that determines whether the bead survives.
A tub full of water with a person in it weighs a few hundred pounds. Under that load the tub deflects, and the gap between the tub and the tile opens to its widest. Seal an empty tub and you have sealed that gap at its narrowest point, so the first bath stretches the bead beyond what it can take and peels it off one edge. That is the single most common reason a fresh joint fails within a month.
Fill to just below the overflow before you lay a bead, and leave the water in until the silicone has cured. The joint then sets at its widest, and spends the rest of its life being gently compressed rather than stretched.
This one is trade and community practice rather than a printed manufacturer instruction. It is the most repeated fix in DIY plumbing discussions about resealing a tub, and the mechanics behind it are straightforward enough to trust.
5. Mask both sides
Two lines of painter's tape, one on the tub and one on the tile, set the bead width for you and give you a clean edge that no amount of careful tooling will match. Leave a gap between them roughly the width of the joint plus a little.
6. Cut the nozzle small, at 45 degrees
Start smaller than you think you need. A narrow bead cures faster and more completely than a thick one, because silicone cures from the outside inward and depth is what the cure has to travel through. A fat bead skins over and stays soft underneath for far longer than the label suggests. Two thin passes beat one thick one.
7. Lay the bead in one continuous pull
Keep the gun moving at a steady speed with steady pressure. Stopping and restarting leaves a thin spot, and thin spots are where the joint opens first.
8. Tool it before it skins
You have roughly 10 minutes with most silicones, and less in a warm humid room. Draw a wet fingertip or a tooling blade along the bead once, firmly, to press it into both surfaces and leave a slight concave face. Once, not repeatedly. Then pull the tape away immediately, while the silicone is still wet.
9. Leave it alone, and leave the water in
Keep water off the bead for the window on the tube, then drain the tub and keep it out of use until full cure. The planner below turns the label figures into an actual time.
When can you run the water again
Using the tub too soon is the most common reason a fresh bead fails. Three questions.
Drying time, durability and upkeep
Three factors decide which product suits a given job: how long it takes to become usable, how long it lasts, and how much attention it needs.
| Factor | Acrylic latex caulk | 100 percent silicone sealant |
|---|---|---|
| Tooling window | Roughly 10 to 20 minutes | Roughly 10 minutes, less in humid air |
| Before water contact | Per the label, commonly several hours | Per the label. GE's data sheet for Advanced Silicone 2 Kitchen and Bath states water exposure is possible in as little as 30 minutes under its stated conditions, and that otherwise the sealant should not be exposed to water for 8 hours |
| Full cure | About 24 hours | About 24 hours, with GE specifying no touching or cleaning for 24 hours. Longer for a thick bead or cool dry air |
| Service life in a wet tub joint | Shorter. Expect to redo it sooner | Up to about 5 years |
| Upkeep | Keep it dry and painted | Wipe down, ventilate, watch for mildew at the edges |
A note on that service life, because you will see much longer numbers quoted. Twenty years is a figure that belongs to sealant in a dry, static joint, not to a bathroom. A tub joint lives in steam, gets scrubbed, and moves every single time the tub is used. Around 5 years is the realistic planning figure, and a joint that reaches it without staining has done well.
There is also a genuinely counterintuitive difference in how the two cure. Silicone cures by reacting with moisture in the air, so a warm steamy bathroom speeds it up. Acrylic latex hardens by giving water up to the air, so the same steamy bathroom slows it down. Same room, opposite effect, which is worth knowing before you decide whether to run the fan.
Why the last bead failed
If you are resealing rather than sealing for the first time, the reason the last one went is worth knowing, because otherwise you will reproduce it.
| What you are seeing | What actually happened |
|---|---|
| The bead peels away cleanly in a strip | It never bonded. Either it went over old silicone, or the joint was damp or soapy when it was laid |
| A gap opens only when the tub is full | The bead was applied to an empty tub, so it is being stretched past its limit on every use |
| Black staining through the bead | Mildew was sealed in rather than cleaned out, or the product carried no mildew resistance |
| A straight crack along the middle | Acrylic latex or grout in a joint that moves. Rigid material, moving joint |
| Soft and gummy weeks later | The bead was too thick and the inside never cured, or the air was too dry for silicone to cure properly |
| Water behind the tile despite a sound bead | The failure is not at the joint. Look at the waterproofing layer behind the surface |
If the tub itself is the problem rather than the joint, resealing only buys time. The warning signs that a bathtub needs replacing are worth checking before you spend an evening on a bead, and if the answer is replacement then our guides to removing and replacing a bathtub and to the surrounding tub surround pick up from there.
What about grout and plumber's putty
Two other materials come up when people seal a tub, and both are right for something other than the job they get used for.
Grout does not belong in the tub joint
Grout is rigid, and the line where a tub meets tile is a change of plane. Under the tile industry standard TCNA EJ171, every change of plane and every tile termination requires a movement joint filled with a flexible sealant rather than grout. Grout in that line cracks, because the joint moves, and then it wicks water into the wall through the crack it just made. If a previous owner grouted the joint, that grout has to come out before silicone goes in.
Plumber's putty belongs at the drain, with one important exception
Plumber's putty is not a temporary material, and it is not a general tub sealant either. It has one proper job on a bathtub: bedding the drain flange, where it stays soft so the flange can be pulled and reset without cutting anything out. It is a compression seal, not a movement joint.
The exception matters if you own a stone resin or marble tub. Plumber's putty stains porous and composite stone, leaving dark rings around the flange that do not come out, which is why the standard practice on stone and cultured marble is to bed the flange in 100 percent silicone instead.
This is not a theoretical concern for us. Badeloft's own installation instructions for the EZ Drop-in Drain call for a small dab of clear silicone around the drain body rather than putty, precisely because our tubs are stone resin. If you are installing one, follow the drain's own sequence in our guide to installing a freestanding bathtub with the EZ Drop-in Drain, or the broader walkthrough in how to install a freestanding bathtub. Where a drain manufacturer specifies a material, their instruction beats any general rule, including this one.
Common questions
Is caulk an adhesive
Partly. Caulk and sealant both grip the surfaces they touch, which is enough to hold a light trim piece or stabilise a panel, and that is why they are sometimes described as light adhesives. They are not structural adhesives. Nothing in a bathroom should be held in place by a bead of silicone alone.
Can I put new silicone over old silicone
No. It will not bond, and it will fail sooner than the bead underneath it. All of the old material has to come out first.
Can you paint over silicone sealant
No. Paint will not adhere to 100 percent silicone and peels away in sheets. If a bead has to be painted, use a paintable acrylic latex caulk, and keep it out of the wet joint. Where painted trim meets a tub, run silicone in the tub joint and stop the paintable caulk short of it.
How long before I can use the shower or bath
Read the tube, because the range across products is wide. Fast cure silicones advertise water readiness in as little as 30 minutes under stated conditions, while the general figure on the same data sheet is 8 hours, and full cure is around 24. A wide bead in cool dry air takes longer than any label number.
Why does my tub joint keep cracking in the same place
Almost always one of two things: a rigid material in a moving joint, or a bead that was laid on an empty tub and gets stretched every time the tub fills. Fix the material, fill the tub before you seal, and the crack usually stops coming back.
Clear or white silicone
Clear is more forgiving of an imperfect bead and vanishes against stone and dark floors. White looks crisper against white tile and shows mildew earlier, which gives you warning before the staining sets in.
The short version
Sealant is a kind of caulk, and for the joint around a bathtub it is the kind you want: 100 percent silicone, kitchen and bath grade, mildew resistant. Strip the old bead out completely, fill the tub before you seal it, cut the nozzle small, tool it once, and leave the water in until it has cured. Save paintable caulk for the trim, keep grout out of the joint entirely, and keep plumber's putty away from stone.
Get those right and a tub joint will give you about 5 good years. Get the fill step wrong and it will give you a month.
If you are planning a new tub rather than repairing an existing one, our collection of stone resin freestanding bathtubs is where to start, and each one is installed to our own freestanding installation instructions, so you know what goes at the drain and what goes at the floor before the tub arrives.