How to caulk or recaulk a bathtub or shower enclosure

Don't ignore loose caulk!

In a nutshell, caulk is used in a tub or shower enclosure to keep water from creeping up, under or around the tiles at joints between tile and the tub or shower pan, or on joints where walls meet. Leaky caulk is not to be ignored!  I have often seen tiled bathrooms where the two or three bottom rows of tiles were loosened by water which crept up under the tiles from the bottom!  The repair can be time-consuming and expensive.  And you might not be able to use the enclosure again for a week or more while things "dry out"!

Caulk can be used as a glue and a sealant

Caulk works because it is both a strong glue and a flexible sealant, characteristics necessary to seal a joint between dissimilar materials or a joint that has movement.  In the damp environment of a tub or shower, the right caulk keeps the water where it belongs and protects your home!

Before you read this article...
Please note that I may use the terms "water-based", "latex", "PVA" or "acrylic latex" somewhat loosely and even interchangeably.    Undried water-based caulks can be cleaned from hands and surfaces with soap and water.  There are no oil-based caulks that are acceptable for interior bathroom use.  Silicone caulks cannot be cleaned up with anything, so care must be taken to keep them off of your hands and any absorbent surface you don't want permanently stained.)

The Winning Strategy... remove the old caulk, clean the surface meticulously and THEN apply the new caulk.

The best way to keep your caulk in tip top shape is to apply it properly in the first place. So, the first step in replacing caulk is getting all the old caulk off. Though you can do a patch job that will last for a brief period of time, a complete job gives the long lasting results.

Pre-clean the work area...

This is a vital step to a successful job. By pre-cleaning the area with a good combination bathroom surface cleaner / soap scum remover before removing the caulk, you will introduce less moisture around the tiles than you would if you cleaned afterwards. After the old caulk is off, the final cleaning will be done with alcohol... more on this later.

Remove the old caulk...

Try to determine the kind of caulk currently installed.  It will help you to plan the removal!  Get a sharp knife and try to cut it. If it is very rubbery and somewhat soft, it is most likely a pure silicone caulk. If it seems to be very hard, then it is probably a water-based latex or PVA caulks, such as Loctite "2 in 1" (formerly Polyseamseal), Phenoseal, or one of the hardware store brands.

Silicone caulk can be removed with a sharp, single-edged razor in a razor blade holder.
Be very careful to keep the razor angled low so that you don't scratch the tub or shower pan, especially if it is a plastic or fiberglass. A utility knife can also be used to cut the caulk from between the tiles and the tub if the razor can't quite get it out, especially in deeper pockets and corners! Sometimes, if you have a porcelain tub, little black lines will appear on the porcelain as you scrape off the caulk, even though you know you didn't scratch the surface. These marks usually come off with the alcohol wipe. If they don't, use a little scouring powder or Soft Scrub... with a minimum of water.

A heat gun can be used to soften hardened water-based caulk.
Many latex or other water-based caulks are flexible, but still set very hard!  Hot air will soften caulk and ease removal. (Sorry, bringing your spouse into the shower will not work.)  Set the heat gun at a low temperature (under 300 degrees F, or your gun's lowest setting), to protect the surfaces and your hands. Keep the heat gun moving to prevent overheating of any area... you want to heat and soften the caulk, not cremate it! Work your way around the enclosure, softening the caulk first and then using your tool to remove it. This strategy is unnecessary for silicone caulks because they are softer and easier to remove.

Once the caulk is scraped off, the area should be thoroughly cleaned.
Wipe the joint down with denatured alcohol and allow it to dry for a few minutes. The alcohol does a good job of cleaning off any remaining soap scum, grease, or other nasties and yucks that may have crept under loose caulk or you may have missed during precleaning. Use a vacuum to suck out any bits of pieces of caulk that may be lurking under the edge of the tile.

Unfortunately, the alcohol will not kill mildew.
If the area was heavily mildewed, you may want to spray it with a concentrated mildew killer after the alcohol wipe. The alcohol cuts the soap scum better than most anything, and gives the mildew killer a fighting chance to knock out any residual mildew. Let it sit for a few minutes, then wipe off any residue with a sponge, rinsing frequently in hot, clear water (no soap). Then, you can use your heat gun to blow dry the area to be caulked if you are in a hurry, or just wait overnight and proceed tomorrow!

It is always a judgment call whether or not to wait overnight or longer before recaulking the enclosure.
If you are replacing the caulk because of leakage, or if it was obviously falling off, you would be wise to put a small fan or heater in the enclosure and let it dry out at least overnight.

Sometimes, the caulk is not leaking but is only discolored from mildew.  If this is the case, you can recaulk immediately as long as you are using a water-based caulk because it will adhere to a slightly moist surface.

If you are using silicone caulk, then there is no debate... the enclosure must be dry as a bone or the caulk will fail! (More on choosing caulks below.)

If you have a recurring mildew problem... reappearance in a few months or less... let the enclosure dry more thoroughly next time you caulk, as long as a week in some cases.

Choosing a caulk... Acrylic latex vs. PVA (polyvinyl acetate) vs. 100% Silicone vs. Siliconized Acrylic Latex

If you are working with a tiled enclosure and a ceramic tub, you can use any bathroom-type, mildew-resistant caulk. I prefer PVA and acrylic latex caulks because they seem to be more mildew resistant, are long-lasting and can be more thoroughly removed from bathroom surfaces.  Cleanup is also easier because they can be washed off with soap and water.  However, they dry somewhat harder than silicone caulk.

The exception is if you have (1) a fiberglass tub with ceramic tile walls, (2) a completely fiberglass sectional enclosure or (3) one of those three or five-piece tub surrounds with caulked joints.  Because it is relatively soft, 100% silicone caulk is the recommendation of many fiberglass enclosure manufacturers. It is easy to work with, has good smoothing qualities and can be removed, when necessary, without cutting into the enclosure.

The biggest downside to EVER using silicone caulk is how difficult it is to completely remove from surfaces when cured!  Since nothing sticks to cured silicone caulk (including itself) any residue left behind will be a point of possible leakage or failure in the new caulk.  Also, silicone caulk leaves a slimy residue on your hands that will not wash off with anything.  I've tried every solvent, soap, and hand cleaner and none work! Even the GE Silicon web site is silent on this pervasive problem! The only cure for the silicone "greasies" is that tried and true cure of many of life's torments... time!

Loctite "2 in 1" Seal & Bond Tub and Tile (formerly Polyseamseal is one of the more mildew-proof PVA caulks available.  I was skeptical when the product first became available so I first tried the product in my own home. The stuff deserves high praise. It does indeed stay mildew-free longer than any product I have ever used, and under the most adverse conditions... my kids' bathroom!! I have used it successfully in all types of enclosures, though you will have to use a heat gun to remove it in a fiberglass enclosure, as mentioned earlier.

Needless to say, there are quite a few other PVA caulk brands that offer excellent mildew resistance. If they are intended for bathroom usage, or labelled indoor/outdoor, they most likely have high levels of mildewcide... a chemical additive that helps the caulk resist mildew for may years.

Siliconized caulks are a hybrid that supposedly have the adhesive qualities of latex caulk but are a little softer and more flexible. I just don't see a clear advantage to them, advertising notwithstanding. Since silicone is a product designed so things don't stick to it, how can mixing silicone and latex improve the product, other than give the manufacturer a new advertising angle?

Just be sure the caulk you choose is a bathroom tub and tile caulk with mildew resistance.

Important: Do not use EXTERIOR CAULKS in the tub or shower.  Though you might think they would be even better than interior ones, you couldn't be more wrong. 
They are designed for different purposes and to stand up under different environmental conditions. Only use caulks designed for bathrooms in bathrooms!!

Fill the tub with water before caulking? Maybe...

Many plumbers feel that a tub should be filled with water prior to caulking.  The principle is that the weight of the water will settle tub slightly downward or, in the case of plastic enclosures, expand it slightly outward.  Thus, the caulk seal will last longer because it will never be stretched when you enter the tub... it will be "pre-compressed".

It this true?  Properly installed, quality tub and shower enclosures will normally not move enough to exceed the expansion (and adhesion) of the caulk.

What to do?  If you don't mind leaning over a tub full of water while you caulk the back wall, there's no harm and it could be helpful.  I have probably recaulked 200 tubs over 30 years and only had a couple of callbacks regarding caulk failure that I could attribute to tub movement. And I never fill them with water.  However, I can't speak to your own tub so take this with a grain of salt.

So, as with most things home repair, it is left up to you.  As I said, this is the preferred technique of many professional caulkers, so I won't discourage you if this is your preference.  You could have one of those unstable tubs... who knows?

Just don't drop the caulking tube in the tub!

Applying the new caulk...

This is the part of the project that separates the mice from the rats. It's a sad truth that, no matter what pains you go through to prep the enclosure, carefully pick the proper caulk, terminate the mildew... all anyone is going to notice is your artistic application of the caulk!!

Having a caulk job look professional is a tall order, mostly because there are few professionals at caulking. In new tile installations, joints that should be caulked are grouted, only because it is a pain to leave the horizontal and vertical seams grout-free for caulking.

Caulking is more of an art than a craft, a mixture of finesse and experience. And every job turns out a little different... some better than others. Even the type and texture of the tile can affect the quality of the job. And using white caulk with colored grout is about as frustrating as you can get!

However, don't loose heart! I can give you a few guidelines that may help you do the best possible job:

Forget about the ice cubes and special "smoothing" devices that look like gynecological instruments! Raise up your hands and look at them... you are seeing ten custom made tools for smoothing caulk! The technique I use is simple:

What about really large gaps?

If the tub was originally installed out of level, the tile installer sometimes leaves too much of a gap above the tub.  It should be no more than 1/4" but I've seen gaps as large as 3/4".  To caulk a gap this wide you have two choices

1)  Fill the gap in multiple steps, allowing the caulk to dry overnight till you have built it up to fully seal the crack.  The final coat can be the "decorative" coat, which is thin and can be smoothed to fairly even finish.  If you try to do it in one coat, you will invariably get a sloppy, smeary job.

2) Put "backer" material into the hole and then coat it with caulk.  There is a foam backer material available in various widths in many hardware stores.  There is also an older product called "oakum" that is a waxed rope used for similar purposes.  Both of these materials were designed to fill gaps under exterior siding, but they will work well... in some circumstances... in tubs enclosures also.