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.
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Before


After


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

Resources
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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