Contractor who remodeled our bathroom used non-sanded grout between bathtub (acrylic) and first layer of tile. He said that he recommends that instead of caulk as caulk will be trapping moisture and grout is better against mold. Now, year after, I see the grout along bathtub cracking and mold appearing in it. So what should I do? I am thinking of scrubbing some loose grout and refilling. But should I use grout again or should I use caulk this time? If caulk, then what kind of caulk should I use?

5 Answers 5


In all the shower installs I overseen, the company I worked for maintained that caulk is to be used in any inside corners except where excessive/standing water is. For example, caulk corners where tub and walls meet, and vertical inside corners where the walls come together. DO NOT caulk where the floor and walls meet, I personally seen caulk creep out of the joint after a week of use in a residence I worked on while I was finishing up the punch list.

Find a reputed mold/mildewcide to clean the joint after you clear all the old grout then allow to dry as long as possible and use a color matched caulk. This is available at Home Depot or at tile supply houses. It is available in sanded or unsanded.

In theory, it may trap moisture, but when the tile is installed and the grout sealed, which should be the case, between the tile being water impervious and the grout has been sealed from moisture infiltration, the amount of water getting past both those points is very minor in my opinion, I read this is so elsewhere.

11-30-2013 addition

To clean the joint of old grout, protect the tub with blue painters tape, maybe a few layers and use a razor knife to begin to V cut the grout out, again be careful the side of the razor knife will be rubbing very hard on the tub/tape and can wear through readily. There is a grout saw available at hardware stores, but they will cut a joint about 1/8" wide, most tile is set closer. If you use this, use a metal shield of some sort to protect the surface of the tub. A large drywall knife (12") would work or a section of very thin gauge metal purchased from a hardware store where they sell small pieces of flat metal. Careful with this, it must be kept secure from moving or the metal will deposit gray marks on the acrylic. Tape it to the tub at the ends and let the metal go up to the face of the tile so any scratches is covered by the new caulk.

To caulk, first the joint MUST be clean and dry, cut the tip to the size of the joint, and apply caulk. Look as the caulk is exiting the tip to ensure the caulk is going INTO the joint, this is where the work is done by the caulk, This why it must be clean. Yes there will be caulk EVERYWHERE to a degree. This is why I keep a 5 gal. bucket handy half filled with water and a rounded edge sponge to clean the surface. Paper towels won't last in the cleaning process, and it may gouge out the caulk if a folded corner of the paper towel goes awry.

To clean the excess caulk, with the wetted sponge, squeezed the daylights out of it to get most of the water out of it. It is imperative you are not depositing too much water on the surface of the tile, it will weaken the caulk. You can clean the caulk from the surface completely leaving the caulk only in the joint and with the color matched caulk, it will look like the other joints on the wall. These caulks are specified to tubs and showers.

  • Can you recommend a good mold/mildewcide? Also, is silicone caulk even water washeable? I was caulking toilet with silicone and water didn't wash it off at all.
    – Uncle Meat
    Commented Nov 30, 2013 at 19:55
  • I have used X-14 to clear basement walls of mildew. Looking online, the results come up with diluted bleach as the product to use, which if I remember right, that what X-14 is, for the most part. Ammonia is suggested too.
    – Jack
    Commented Dec 3, 2013 at 1:46
  • I read the first paragraph a few times and I'm still not sure if Jack is saying to use caulk or grout between the tub and tile.
    – orrd
    Commented Nov 21, 2018 at 21:51
  • It does say use caulk where tub and tile meet, and grout where shower floors meet the walls. Caulk can handle the occasional wetting of water at the top of a tub, but cannot handle the saturation of water at the level of a shower floor, that is where grout is recommended.
    – Jack
    Commented Nov 22, 2018 at 3:40

My Uncle was a plumber, so I called him, before re-caulking my newish bathtub for the 3rd time. I told him that no matter how good a job I did, scraping & cleaning out the old caulk, spraying a bleach & water solution into the crack, to kill any mildew that might be present, then wiping it down with a clean, damp cloth, once dry, then laying down the caulk, wetting my finger and smoothing it down, to perfections, that within a couple of months I'd get gaps between the tub and the wall tile, and the orangish mildew would return. He told me that what most people forget is WEIGHT. When you lay down the caulk you must have the approximate weight of a person, who'd be using the tub or shower, IN the tub, or despite the beautiful caulking job you've done, the moment someone gets in to use it, the added weight to the tub will separate the caulk from the joint. He told me that depending on how good the bathtub seal is, he simply fills the tub at least 1/2-3/4 of the way with water, OR if the tub seal won't hold the water, he puts at least 4 bags of dry cement mix (you could perhaps use play sand) in the tub, for weight.
Since our tub was new, the seal held perfectly, held the water, we THEN laid down a nice thick, smooth bead of caulk, left the water in for two days, then drained it and voila, no more gaps going on almost 2 years now.


Hope these tips from my experience doing caulking around tubs and showers help:

  • Take your time. Don't rush it or you'll be doing it again within a year or two. It might take two nights to get the old caulk all out. So what. You want a job that will last.
  • Clean out all the old caulk. Use a 1" paint scraper, razor blade scraper, knife, maybe high grit sandpaper so long as the part sanded will be caulked over.
  • Buy the most expensive Tub and Tile caulk you can find. I prefer GE. You don't want to have to do the job again and $10 - $15 isn't much when you consider the aggravation of redoing it.
  • Right before caulking saturate a portion of a clean cloth with rubbing alcohol and force it into the joint. Wipe it once from each direction to make sure its clean. Then let it dry.
  • Cut the caulk tube diameter to the width of the average gap.
  • Caulk the gap, not the tub or tile outside surface. The caulk needs to contact both inner surfaces, but for aesthetics, don't overlap the two outside surfaces more than about 1/8".
  • Have a roll of toilet paper handy
  • After caulking the gap along one wall, dip the smallest finger that will bridge the gap in rubbing alcohol and quickly and firmly wipe straight down the gap. If not suitable, wipe the finger with a piece of toilet paper, fold, discard, re-Hopdip finger in alcohol, and repeat.
  • Make it a habit to keep your hands clean at all times or you'll end up with caulk in places you don't want it.

Good caulking :-)

  • Please be very careful scraping this joint out at the tub! Acrylic surfaces scratch very easily.
    – Jack
    Commented Nov 30, 2013 at 12:43

I've always heard that there should be a small gap between the tile and the tub, and that gap should be filled with silicone caulking. I found this video really helpful for getting a perfect bead of caulk around the bathtub. It involves setting up some tape to use as a straight edge, and using a plastic spoon to smooth the caulk (instead of the normal finger method).

I've used this method and the caulking turned out perfectly.


Your contractor is wrong. This joint should always be caulked with a silicone mold resistant kitchen/bath type caulk, as should the vertical inside corners of your tub walls. Make sure you clean out the grout joint completely and let it dry thoroughly so you have a clean surface to attach the caulk to.

Then prepare to ignore it for around 15 years...

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