# Tub caulk - Touching up a spot.



## cjaustin81 (Sep 4, 2014)

I caulked my tub a couple months ago w 100% silicone caulk. There's two spots where the gap between the tub/tile was bigger than the rest. The caulk has sunken in where these areas are, but no gaps or cracks exist.

Can I touch these two areas up w caulk after I clean the area? Or do I have to remove the bead of caulk on that side and use a backer and recaulk?

Where the corner is here you can see its sunken in.









This is before I caulked.









Originally they had some hard material in there, which I removed. Wasn't sure if this was old caulk or not.









The other spot where the caulk has sunken in is under the tile in the top right corner.









Should I have used a backer rod in these 2 spots?


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## Nestor_Kelebay (Jun 17, 2008)

No, the smallest backer rod available is 1/4 inch, and there's no way you'll be able to squeeze that backer rod into the gap anyway.

You don't use backer rod when caulking a tub anyhow.

I'd be reluctant to "touch up" those two sections. Silicone caulk won't stick to silicone caulk, so the only way to do it would be to use a razor to cut through the silicone on both sides of that recessed area in Photo #1, remove the silicone between the cut lines and recaulk that spot.

The problem is that the silicone you put in won't stick to the "ends" of the silicone that's there, and considering that spot is right at the corner of the tub, you could have a water leak between the new silicone and the old there.

If there's no water leakage, I'd just leave it the way it is.

So far as the sunken spot under the tile in Photo #4, I'd just fill that in with an acrylic grout sealer, like Tile Lab "Gloss Sealer & Finish" which you should be able to buy at Home Depot. Clean the spot well with a toothbrush and phosphoric acid, and then just use a small artist's paint brush to apply acrylic grout sealer so as to "fill in" that spot. It may take repeated thick coats to fill it in.

Phosphoric acid is the active ingredient in most bathroom cleaners as well as very many toilet bowl cleaners. It's used to clean bathrooms because it easily cuts through soap scum, but doesn't attach chrome plating at all, even at high concentrations. You can buy gelled phosphoric acid toilet bowl cleaner at most hardware stores and home centers, but if they don't have it, EVERY PLACE listed under "Janitorial Equipment & Supplies" in your yellow pages phone directory will sell a phosphoric acid based toilet bowl cleaner.


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## cjaustin81 (Sep 4, 2014)

Nestor_Kelebay said:


> No, the smallest backer rod available is 1/4 inch, and there's no way you'll be able to squeeze that backer rod into the gap anyway.
> 
> You don't use backer rod when caulking a tub anyhow.
> 
> ...


When I googled this, there were a bunch of articles showing people filling in gaps around the tub with a foam backer-rod. They said you want the backer to be 1/8" larger than the gap. 










As far as the acrylic grout sealer, that looks to be just for sealing. How would that "fill in" that gap under the tile? 

Even if I were to cut out a section and re-caulk in that spot, my concern is there's nothing behind it to prevent it from sinking in again. 

I've caulked under pic 4 a couple months ago. That caulk is still waterproof.. the problem is the caulk sunk in so there's not much caulk on the tile.. rather it's inside the tile but still forming a bond.


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## ilo55 (Mar 21, 2015)

Silicon is a blank cartridge ( pump it could be a cream) white cement fill (you get a soft cream consistency).With this fill in the blanks.Correct.After drying,apply the silicone and pull the tape from the two sides.A small spoonful of plastic,silicone and soak it in soapy water with it correctly.Bands immediately (before drying) to remove it.

Regards


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## Nestor_Kelebay (Jun 17, 2008)

cjaustin81 said:


> When I googled this, there were a bunch of articles showing people filling in gaps around the tub with a foam backer-rod. They said you want the backer to be 1/8" larger than the gap.


Well, truth is that you can find just about everyone saying everything on the internet. Newbies come to these Q&A forums because they want to know what's real and what's bogus.

Backer rod is meant for deep gaps of constant or narrowing width. That's because caulk works best when it's thinner in depth than it is wide. Caulk is meant to stretch and shrink with any movement across the gap as well as seal the gap when there's lateral movement between the two sides of the gap, and filling a deep gap with caulk causes the caulk to let go on one side or the other. By using backer rod in that gap to ensure that the thickness of the caulk is less than it's width, you allow the two "ends" of the caulk to move relative to each other without either end letting go of it's side of the gap. That is where and why you use backer rod, NOT because it saves on the cost of expensive caulk, which is the popular misconception.

Further, every enameled steel tub has a rim around it which is about an inch high. The bottom edge of the tile backer board should be from 1/8 to 1/4 inch above that rim. The bottom row of tiles then hangs down in front of the rim. So, you can have a fair bit of space between the bottom row of tiles and the rim around the tub. Pushing backer rod under the tile is as likely as not to end up with that backer rod ending up in that space behind the bottom row of tiles. And, if so you'll have a fight on your hands trying to get it out of there.

Finally, the bottom row of tiles should be cut so that they come down to about 1/16th of an inch of the top of the tub. You simply can't squeeze 1/4 inch backer rod into a 1/16th inch gap.

When you caulk, simply run a dry finger over the wet silicone caulk, and that will be enough pressure to squeeze silicone under the bottom row of tiles, and that's all you need. When you remove the silicone in future to re-caulk, it's not necessary to remove the silicone under the bottom row of tiles. (but you can if you want to, and it's not hard to do with the hook blade from a utility knife held in the jaws of a needle nose set of locking pliers) As long as you get ALL of the silicone off the bottom tiles and the tub, then the new silicone will stick well to the surfaces it needs to.



cjaustin81 said:


> As far as the acrylic grout sealer, that looks to be just for sealing. How would that "fill in" that gap under the tile?


An acrylic film forming grout sealer (like TileLab's Gloss Sealer and Finish) forms a clear film as it dries just like latex paint forms a film as it dries. You just apply multiple coats of the sealer to the depression and it will seal that depression you have under the tile to ensure no water gets into the wall at that spot. If you continue applying coats of sealer, you wouldn't have any trouble actually filling that depression with clear plastic sealer so the sealer is flush with the grout on each side.



cjaustin81 said:


> Even if I were to cut out a section and re-caulk in that spot, my concern is there's nothing behind it to prevent it from sinking in again.
> 
> I've caulked under pic 4 a couple months ago. That caulk is still waterproof.. the problem is the caulk sunk in so there's not much caulk on the tile.. rather it's inside the tile but still forming a bond.


Really what the problem is here is that you're either not putting enough silicone on before you spread it with a dry finger, or you are pressing too hard with your finger, thereby pushing the caulk in too far.

Remember that the caulk only has to seal between the tub and the tile face, and even the lightest finger pressure will ensure that. Using more pressure on your finger simply forces more caulk under (and behind) the bottom row of tiles, and that doesn't do you any good. It doesn't do any harm, but it doesn't do any good, and in your case it's making you want to recaulk spots where there isn't enough caulk between tub and tile. Better to apply more caulk NEXT TIME, use a lighter finger pressure, pull your masking tape off, and then dip your fingers in a 50/50 solution of dish washing detergent in water, and tool the joint so that it looks pretty. And, only do 2 or 3 feet of caulk at a time or it'll start to dry out on you and running a dry finger over it will make a mess of it.


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## Nestor_Kelebay (Jun 17, 2008)

CJAUSTIN:

It wasn't until I sent that last post that I saw the picture of your gap. I have never seen a gap that wide between tub and tile.

That is bizarre.

Yes, if I were you I would use foam backer rod in that gap.

Your picture doesn't show enough of the tiling to be able to tell if those tiles are square or rectangular. If the tiles are square, the installer should have cut that bottom row of tiles so that it fit down close to the tub as seen in your previous pictures. The way he/she has installed those tiles there's far too large a gap between tub and tile.

I would be inclined to "fix" that by first siliconing a strip of 1 inch wide 18 or 20 gauge stainless steel sheet metal to the front of the bottom row of tiles, allowing that silicone to set up, and then caulking between the steel and the tub. Either that or use foam backer rod and goop a 1 inch wide swath of silicone across that joint.

The gap between tub and tile should be like the gap shown in the first pictures in this thread.


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