How to Caulk a Bathtub

I've recaulked this bathtub twice already in the five years that we've been here. Being male, I'm blind to most dirt, grim, mold, and mildew. My wife though is not. I never notice the mold or mildew in the tub, but she does. Not only that, but it drives her absolutely nuts.

So when I asked what she wanted for her birthday, and she replied, "fix the bathroom caulking, it's gross!", I thought If I have to do this again, I'm going to research it first and do it right this time. It' a lot more work doing it correctly, but hopefully this will last... longer anyway.

Two article on the web (after a bunch of searching), really seemed to be on target, and are the basis for the steps that follow for how to caulk a bathtub. I suggest you read these articles as well.

The Natural Handyman: How to Caulk or Recaulk a Bathtub or Shower Enclosure
House Repair Talk: Bathtub Caulk: See posting by Nestor Kelebay

Credit, and thanks goes to Jerry Alonzy and Nestor Kelebay for those great articles.



The corner shown in the "before" photo above was the worst area. You'll notice that the gap between the bathtub and shower tile has quarter round ceramic tiles. I searched the web for a while and couldn't find anything like this arrangement. I then concluded that they were either used for decorative detailing or to hide a large gap. Seemed to me they needed to go, as they created too many seams where caulk could fail, leak and harbor mold and mildew. Cleaning just the surface, wasn't an option, as it seemed the mildew was coming from behind the quarter round tile. Note: You can click on all photos to enlarge them.

Here's the whole tub. I never see the mildew, but she does. I believe the tub is fiberglass with an acrylic finish. The shower walls are ceramic tiles with grout between them.

Here's a close up of my really bad previous caulk job. I did the typical bad quickie job here; put down a bead of caulk, spread with my finger... done in 10 minutes for less... and it shows, and failed, twice.

Here's the better way.
Step 1: Removing the old bathtub caulk

I have ceramic quarter rounds to remove here, whereas you'll most likely only have caulk. The following photos show the mechanical means of removing the old caulk. Start with a utility knife, or razor blade scraper, at a low angle, to cut the caulk seal. The low angle is so that you don't cut or scratch the tub, or shower enclosure.

Then use a putty knife (or a drywall tool, couldn't find my putty knife) to remove the old caulk.

Women often know best. Look what was lurking beneath the surface. This also means water was leaking behind the corner of the tub too.

Here's that same area, showing mold and mildew beneath the removed tiles and caulk.

Use a screw driver to remove caulk from the gap between the shower walls and tub. Be careful not to chip/crack/damage the tiles or the tub.

Behind the quarter round ceramic pieces was filled with my old caulk job, so I had a lot to remove.

Remove as much caulk as you can with mechanical means before going to step 2.

Can you see the sweat? It's actually quite hard work.

Step 2: Removing ALL (microscopic) old Caulk

If you click on the photo to enlarge it, you will see a thin layer of caulk on the wall that needs to come off. And here my friends is the most important point of this entire article. YOU MUST remove ALL of the silicone caulk before applying new caulk. And here's why. Silicone caulk does not adhere to itself! So if you have even so much as a microscopic layer of silicone caulk left and then apply new caulk, it wont stick for long. You should test a small spot on your bathtub and wall before applying any chemicals to be sure it does not stain or have other bad results...

Here's how to remove all of it. Lay down some folded over paper towel strips at the gap, and soak them with mineral spirits. There is also a specific product for this, from DAP, called Silicone Be Gone™, it's a gel form of mineral spirits. I could not find it nearby, so I used mineral spirits which seemed to work nicely. You have to leave it for 1-2 hours without drying, so you cover the paper towels with plastic Saran Wrap. The mineral spirits don't remove the caulk, it just makes it softer so that it's easier to remove.

Turn on your bathroom exhaust fan, if you have one, and put a fan in the window to blow the fumes outside.

Now that the caulk has softened, I'm able to remove even more. By the way, the sharper the blade, the more successful you will be with removal, so buy yourself a bunch of new blades. I had a 100 pack in the basement and used about 10 blades.

Okay and now... You're going to soak it with mineral spirits again to get off even more. It's time consuming, but it's the only way to get the new caulk around the bathtub to adhere well.

Reuse your paper towels. Soak them again with mineral spirits.

Cover with plastic and wait another 1-2 hours. Don't let it dry out.

Do more scraping with the razor blade, and also use things like a stiff plastic brush, Scotch-Brite green scouring pads (more aggressive, but might scratch fiberglass, or acrylic surfaces) or white (less aggressive, but scratch resistant) scouring pads, rub with paper towel, etc. Do everything you can to remove ALL of the silicone, without scratching the shower enclosure, tiles, or bath.

Nestor's article (link above) recommends rubbing a fine powder onto the old caulk area, and where it sticks you will know you have more caulk to remove. You then would repeat the process again for those areas that still had caulk. I tried this with some flour, but nothing stuck, meaning I didn't have any silicone left, or flour doesn't work so well for this trick. I'm not sure.

When you feel that all the caulk is gone, wipe off the area with water.

Step 3: Retarding Mildew and Mold

I didn't find any of the concentrated mold killer as recommended by Nestor. All of the products except for one, only claimed to retard mildew or mold. The one product that was a concentrate and a "killer" said for exterior use only, so I didn't get that. I'm not sure that what I got will do much, but with all mold and mildew remediation, the first step is always to fix the water leakage problem. Hopefully the new, good seal will do just that.

Give it a quick squirt into the gap. Don't over do it as you want this area to be bone dry when you recaulk.

If you've had a more serious leak in this area, you may have water damage, mold and mildew, which could require removal of shower tiles, new wallboard and so on. Fixing serious water damage, and mold and mildew issues is beyond the scope of this article.

Step 4: Clean with Denatured Alcohol

Use a paper towel, soaked with denatured alcohol to clean away any residual grim.

Step 5: Let it Dry Over Night.
You can only apply the new silicone caulk to the bathtub with it is absolutely bone dry.

Step 6: Painters Tape to Control the Application of Caulk

Get moderately wide tape, and for this job, you don't need the version that is for delicate applications, but as you will tape left over you might want it anyway. I find that for painting projects the delicate stuff is a must have. It's more expensive though, so it's up to you.

Apply the tape with a 1/4 inch of tub surface showing and a 1/4 of shower wall showing between the gap and tape. Press it down tightly so that the new bathtub caulk doesn't migrate under the tape, especially at the tile joints if you have them in your shower wall.

Here's a close up of the tape job. The corners of my shower were fine, but I needed to go up the corners a bit with new caulk.

Step 7: Caulking the Bathtub

The Natural Handyman link above has good information on the type of caulk you should use for your tub and shower wall combination. In my case my tub is fiberglass and my shower walls are tile, so I'm using 100% pure silicone caulk, which is recommended by many fiberglass tub manufacturers. You might wonder why you wouldn't use grout around the bathtub. Grout is not flexible, anytime you are sealing between disparate materials that may expand and contract, or move, for example when you fill the tub with water and then add your body weight the gap size can change, so you need flexible material here (caulk) and not grout.

These tubes are made to go into caulk guns. If you don't have a caulk gun you get a get one for less than 10 bucks, or you can buy tubes of caulk that come in squeezable tubes, which may be easy for a beginner to control anyway. One trick with applying caulk is not cutting the hole too big. You can cut the nozzle open with a utility knife, or you might have a cutter like I do (shown above) in the handle of your caulk gun. Cut the hole at an angle and make it about the size of a coat hanger wire.

Then you'll need to puncture the seal within the caulk tube with a nail or you may have a pin on your caulk gun for puncturing the seal, prior to putting the cartridge in the gun.

Squeeze an even bead of caulk into, and along the gap. Do this all in one caulking session. Some people recommend filling the tub 3/4 full with water, to simulate the weight of taking a bath, or taking a shower, which would widen the gap before caulking, to be sure you've got a seal that will accommodate usage conditions. They leave the water in the tub while the caulk is curing. I didn't do that as I don't think my tub moves much, if at all. Also if you fill the tub with water, you run the risk wetting the area your about to caulk.

With your finger carefully smooth out the caulk, so that it is an even thickness all the way around.

Now you can remove the tape, being careful not to disturb the remaining caulk.

Give the caulk a few minutes to skin over, which is also a good time to mix up a small contain of half water and half dish detergent for the next step.

Dip your fingers into the soapy solution and run your finger gently alone the caulk for the final shaping. The soap allows your finger to slide over the caulk without sticking to it. The goal here is to give the caulk a final finished shape and to be sure it is forms a nice seal at the bead edge. Do not flatten the caulk so much that it makes a feathery, thin edge. A feathery edge will be more likely to pull away with time.

And here is the final result. A good seal around the bathtub that should last for some greater time without leaks, mold or mildew. General maintenance is required to clean this area periodically to prevent mold/mildew. Notes on maintenance to come...--Peter

The Natural Handyman: How to Caulk or Recaulk a Bathtub or Shower Enclosure
House Repair Talk: Bathtub Caulk: See posting by Nestor Kelebay

My Standard Disclaimer: This is what I did. This does not mean this is the best way, the right way, to building code, or even safe for your needs. So you are on your own with your project. I make no promises about the information presented here. I'm just a do-it-yourselfer, not a professional at all, sharing my story. So if something goes wrong with your project, you are on your own. Good luck, and have fun!

All content and photos, copyright 2009, Dover Projects.

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  1. Hey Peter,
    How wide was your gap between the tub and the bottom of the tiles (where it should meet the tub)? I assume you had the ceramic quarter round originally b/c the gap made the original owner to afraid to caulk.
    Is the caulk holding up?

  2. Lee in CentrevilleJuly 4, 2009 at 12:05 PM

    thanks - i wouldn't have thought of using the tape! Also the rubbing alchohol for final cleaning since it dries faster. Just taped and am going to caulk today. FYI one concern I have is how big a gap one should caulk over because the tile was not cut right and there is about a 1/4" gap in a one place along the vertical corner in my shower. Hoping the caulk will work on it's own. Last own had grout and caulk there but I think that was part of the problem of the water getting in there when it the grout cracked. I'm just going to try to get the bead a little thicker and "in there" more in that spot.

  3. Lee in Centreville VAJuly 4, 2009 at 12:11 PM

    Hey Ryan who posted above - you were wondering the same thing as I am about my project - although mine is the vertical corner in a shower. How wide of a gap do you think is too wide for caulk alone? I am not entirely sure I should go ahead and caulk. Is there something made that is like a filler that is flexible but adheres to the drywall underneath and the tile on both sides to sort of fill the gap a bit before you caulk, that is made just for that purpose? The alternative seems to be to retile the whole thing or at least try to take out a few tiles and deal with perhaps the tile color not matching exactly in order to eliminate the gap. Sucks that whoever did this did not cut the tile better.

  4. Peter - thanks for the great article - I found several guides online but yours has the best step-by-step descriptions and photos. Like you I have caulked this shower before, but this time I followed your advice to remove all traces of previous caulk so hopefully it will be better. Your article gave a few tips that I used but I didn't do the denatured alcohol (I felt the mineral spirits had done a good enough job) and I didn't do the wash-up liquid. I've used my finger before, but this time I used a tool for spreading the caulk. The tip on leaving a 1/4 inch either side of the gap was a spot on. The majority of the effort is removing the old caulk - putting in the new caulk was easy, quick and a joy!
    Andy, Richmond, VA

  5. So far the caulk is holding up perfectly, but it has only been 1 month since doing this job.

    If you have a large gap between the tub and the shower tiles, you can use "backer rod", which is made just for this purpose to fill the gap first, giving the caulk a good surface back up against. Any gap larger than 1/4" should first be filled with backer rod (it's flexible, foam-like rope), prior to caulking.

    It's available at home stores and comes in a few sizes. Here's an example:

    Here's a bit more about backer rod this article:

    Also, if you are smoothing caulk over a larger gap, some use the back of a spoon, rather than their finger.--Peter

  6. I had a new fiberglass tub installed by a professional plumber, well worth the expense, I did not caulk the tub surround at the bottom of the tiling but did caulk the verticals. My plumber told me it really is optional to caulk, as if any water does get behind the tile , it will easily drain, if it is caulked , it has no where to go ...any comments??

  7. " I didn't do the denatured alcohol (I felt the mineral spirits had done a good enough job)"

    The Alcohol is inportant because it cleans the Mineral Spirts up, what does leave residue of its own.

    The Alcohol also helps drive out the water.

  8. Anonymous from July 6th, 2009: I didn't respond back then, as I wasn't sure what to say. I'll give it my thoughts now, and someone else can weigh-in with more, or a correction.

    I'd still caulk it for these reasons:
    1. I'd prefer no water to get back there. Who knows how much goes back there and whether it has a chance to grow mold or start to rot. Mold can grow fairly quickly.
    2. It, depending on the fit, might look better than a gap.

  9. Anonymous from August 10th: Thanks for your input!--Peter

  10. Hi Peter,
    I did what you did a few times and kept getting nasty-looking caulk after a few months. Thanks so much for all your tips. I'm going to spend a while on it this time and see what happens!!!

  11. It's only been about 5 months, but so far the caulk is still looking great. My wife cleaned the shower and caulk the other day, and I was like "What! You can't touch that, it's in experimental mode!": 1. I have to take update photos to show if any mold/mildew or other issues have happened, and 2. What did you clean it with?! I got thoughts of her scrubbing it, really hard with a toothbrush, disturbing my perfectly sealed edges. LOL. Well, I'm not sure how she cleaned it, and cleaning IS part of keeping the caulk in good shape, but I wanted to supervise, and document, and make sure she was using approved cleaning fuilds...! LOL.--Peter

  12. Can you help me? I am caulking a bathroom sink that keeps getting dirt and grime in between it and the counter. How do I prevent this? I don't really want the caulk to show like it does on a bathtub. What are your suggestions?

  13. This is a great article! I just recaulked my tub yesterday and only AFTER did I come across this. I am worried I'll have to recaulk again because my edges may be too flat/feathery (I may not have used enough caulk). Also, you mentioned that you used silicone caulk and I did not. I have ceramic tiles that meet with a porcelain tub. Are non-silicone caulks okay, as well?
    - ad

  14. This is one of the coolest help sites on the internet. Thanks as this one is particularly excellent. Helped me with a problem that was resurfaced several times. Should be good to go now.

    The idea of using tape for the edges is great. Just one note is make sure you get all the smoothing/finishing done before you remove them.

  15. Hi Peter!
    What a blessing it is to find your website. As a single woman with a 4 yo who is purchasing her first home, I felt a bit intimidated by the inspectors report for the minor work that needed to be done. The work that I could actually do without hiring it out. Your pics and easy to understand language makes me feel more confident. Like a DIYer! Keep it up!!

  16. This is far and away the best online "how to" article I have ever read-on any topic. Now I know what to buy and how to do it. I agree with the previous poster that it is a blessing to find this.
    I wish you would write a few about changing faucet O rings and washers too. And really, it would be great if you wrote a book. I know I can do these things myself but it is a matter of getting the right information. And here it is. Your wife is lucky to have you (and you to have her I'm sure)

  17. having a problem with acrylic latex caulk.. caulked between tub and bottom tile. cured 10 days before getting wet. once wet surface of caulk is turning white ( beige caulk) seems caulk is absorbing water . is it possible it never fully cured?

  18. Apologies for the late reply, very busy with my day job and Facebook (what a time sucker!). I'm afraid I don't know the answer to your acrylic latex caulk question...

    Also, thanks very much for the nice comments above!--Peter

  19. NEW!!! DOVER PROJECTS ON FACEBOOK! Join in with your DIY spirit! Click on the BIG blue box for "Facebook, Dover Projects" in the right column above! See you there!--Peter

  20. Thank you, this guide is great. We just used it to caulk our tub and it looks like a pro did it!

  21. Anonymous, glad it helped out! Thanks for the feedback.--Peter

  22. Thank you for investing so much time into capturing and then sharing freely what you've learned about home remodeling, and in this case silicone sealant replacement. Please thank your wife for me and let her know that your labor of love is well appreciated, and helps other husbands serve their families by caring for their home. I've come back to this site a number of times over the last few weeks as i had to replace a bathroom shower in our home. All the best to you - Joel G

  23. This is such a great article. Thanks for posting it. I have referred to it many times while fixing my daughter's bathtub!

  24. Thanks for the nice comments people! If you are on Facebook at all, there's a bunch of us sharing our projects there. I'm currently remodeling our entire kitchen. Whooowaa.

  25. I should add that filling the tub full of water is quite necessary for a fibre glass tub. I caulked a brand new tub without filling it with water and within weeks, the silicone pulls apart. The thing is that I could only notice the "cracks" when I am taking a bath (with body weight and water.

  26. thanks for the great tutorial. this will be very helpful. that caulking that you did looks great so I'm sure your wife had a very happy birthday because of it.

  27. Thanks for the site and documenting the process with photos. It's enough of a job without stopping to take pictures and keeps notes!

    I spent extra time on removing ALL the old caulk, prep, and taping. Thanks to your instructions and the new caulk came out great.


  28. Peter, great article. I'm going through the process now. I'm currently removing the old caulk. What cleaning products do you or your wife use now in the shower to ensure that your new caulk job stays safe?

  29. Hi there...
    Great article Peter...

    It would be great if you added a
    "list of ingredients"

    That way assembly of all equipment will be made a little easier.


  30. Hi Peter... My husband and I recently bought my dads home and we are new to having to do our own “fixer uppers”. Most of the time we are lost, so I was so glad to find you!!! We are at this very moment in the process of re-caulking the "gap" between our tub and tiles. I have looked everywhere for what we should fill the gap with. I guess I should have hunted more thoroughly for you before we did what we did... but hopefully you will agree with what we did and say it will be okay!! =) We went to Lowes and found a grout that actually came in a tube… its called sanded caulk, it kinda seems like grout... we actually used that to fill in behind that gap and we are letting it dry as I type this. After a few hours we are gonna caulk. I’m gonna line with the painters tape because thats a fabulous idea!! And we are gonna gunk on the caulking and I’m PRAYING all will go well. Do you think we made a bad decision with that sanded caulkin’?? Thank you so much for posting all your great info on the web… You have saved this couple!!! =)

  31. Nice job I just did all four of my tubs I found using rubbing alcohol softened it enough to remove it all and of course patients and lots of hard work. After four bathtubs I consider myself an expert now if only I can get my husband to do it next time.

  32. Nice article
    Just did my tube following your directions. I owe you a beer.

  33. WOW! This is the best step by step guide I've seen. I would SO hire you to come do mine :). Thank you for your very informative tutorial. I read it all to my husband and he just looked at me with these big eyes lol.

  34. Thanks for the info this was a great article as I am a beginner! There are 1000's out there but this one was simple and an easy read!!

  35. I'm certainly impressed with the makeover. With the what you've shown us, water will surely just drip away right down the spout. Totally moisture free!

  36. Hi,
    Instead of using your finger to even it out, you can use a table spoon. Always dip the spoon in water before taking off a chunk of silicone. This way, it will look more even and straight and it will also have that finished look at the end.

    Great article, Thanks!

  37. Your wife is so lucky!!! Flowers would have been cheaper and far less time consuming.

  38. Great stuff. I suggest filling your tub with water first. It helps open up the caulk areas allowing tighter fill. When tubs fill and empty they expand and contract stretching the caulk areas. After time they eventually begin to separate especially if your tub is against an outside wall.

  39. I am really impressed with how you put this all together to present on the web. Just doing it is one thing, and you did it perfectly right, but taking the time and trouble to document this and then present it is impressive. Good job.

    I understand Gyuri's point about the spoon but for a tub like this the finger tip the way you did it is much better. Also, I understand the other people's comments about filling the tub, but that only applies to certain types of tubs (fiberglass, etc.)

  40. How do you know that there isn't any mold/mildew back in the "crack" before you re-seal it?? Just pulled out a bunch of disgusting sealant, we don't have tile just the plastic tub & wall surround, and some parts have tons of black mold on the back side of it & some have the orange gunk. The shower/tub is only 5 years old & I wonder if the guy who installed it did it right. Im also wondering how bad this is for my health to be pulling out this mold covered stuff & if it's flying around in the air now :/


Please leave your questions or comments here. I love to get feedback. You can do so without an account or user names and passwords, etc. Just select "Anonymous" next to "comment as". Thanks!--Peter