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Jstepson t1_j28zil8 wrote

You can use a thing called backer rod make just for prefilling large gaps prior to caulking they come in different thicknesses and are shoved into gap prior to caulking, gives caulking something to hold onto and if this is a wet area 100% silicone needs to be used. When applying silicone put blue painters tape at the edges of where you want silicone to stop,install silicone then Cann lick finger and wipe one side to other to make sure it's in good. Let set an hour and peel blue tape off should be nice neat line of caulk.Wait at least 12 hours then use shower without fear of water damage.


Bayou_vg t1_j2akuzd wrote

Backer rod is the answer.


SuspiciousChicken t1_j2c9icx wrote

Yes, and in addition to creating a joint that is attached on only 2 sides and can flex properly, it will also solve OP's problem of too much sealant oozing out while drying.

By using less sealant, properly adhered with a backer rod, all of it will perform better.


firstLOL t1_j2b6rkh wrote

You'll get better adhesion to the shower floor and tile if, instead of using a finger, you use a profiling tool (ideally an angled one, not a concave curve that you'd get with the finger).

Concave silicone in areas that get a lot of water (like showers) mean the part that is doing most of the 'work' to keep water in the shower (where the top and bottom edges of the silicone meet their respective surfaces) is often very thin. A suitable straight angle avoids this issue.

One other good thing to do is wipe the area thoroughly with isopropyl alcohol before applying the silicone (giving enough time for it to effervesce evaporate away). Silicone hates soap residues, grit, and especially grease (another reason not to use a finger!), and alcohol is great at getting rid of all three.


damarius t1_j2baa6z wrote


I think you mean evaporate. Isopropyl alcohol doesn't have bubbles. Yes, nitpicky grammar nazi-ish I know. That's how I roll.

Edit: I should have added that this sounds like a sound approach to resolving the problem but I'm not a professional.


firstLOL t1_j2cvdts wrote

Thanks, grammar angel on my shoulder! You are correct, though effervesce is a much more fun word to say.


climbtigerfrog OP t1_j2bp72k wrote



Kleenexexpress t1_j2cb3i5 wrote

I noticed our friend here said to wait an hour before pulling your tape. Not to nitpick but I was taught to pull your tape immediately after your final swipe. But what do I know, I don’t even tape when I do these types of caulk jobs.


Bldaz t1_j2dohq5 wrote

Silicone will start drying before you finish applying, tape will pull it off more the longer you wait. I don’t use tape My choice 1 -That needs to be cleared out first. 2-You can use a silicone grout that matches the existing grout or Try Amp caulking very little sag. Just a simple reminder there’s a 1/4-1/2 “ lip extending upward on that tub you can’t see. Curious if that sub floor is sagging


caramelcooler t1_j2b4oyc wrote

One small note, sealant needs an hourglass sort of shape to expand and contract at the thinner middle part, with the wider top/bottom having more contact with the surfaces. So even using a backer rod when it’s not really “needed” for shallower joints between parallel surfaces can still help, if there’s room.


DoctorKynes t1_j2b5jvb wrote

Do backer rods work for baseboard gaps? Was planning on shoe molding throughout the house but between cutting and painting it would become quite a project.


RidersPainfulTruth t1_j2b6r8n wrote

You’re better off with quarter round. Caulking that much linear footage sucks compared to chopping shoe molding with a miter saw


Tack122 t1_j2b7r2o wrote

Shoe always looks better than quarter round imo.

Quarter round also takes up an annoying amount of space when you want to sit furniture flush against a wall.


akmacmac t1_j2bma6i wrote

I’ve always heard to never caulk the baseboard (or shoe molding) to the floor. Something about too much movement between these surfaces causing caulking to crack/separate). (Except, I think, in bathrooms, for purposes of keeping water on the floor from getting underneath). The alternative to shoe molding would be to pull the baseboards and scribe them to the floor (basically trace the contour of the floor and shave off the bottom edge so it sits tight against the floor). Also agree shoe molding looks much better than quarter round.


ineedhelpbad9 t1_j2c4b08 wrote

I thought that was only for floating floors that aren't attached to the subfloor.


jmm166 t1_j2bmf0j wrote

Gloves. Wet your GLOVED finger. It’s hard to really get off skin.


[deleted] t1_j2a2ff3 wrote



slashfromgunsnroses t1_j2agavk wrote

Silicone is pretty strong and a larger gap actually allows it to absord more movement. With the backer rod it will sit just nicely.

Grout is water permeable and will actually allow water to leak behind causing damage.

Silicone all the way.


md9918 t1_j2b34m7 wrote

I've done this before. The grout will crack because it's brittle and the shower pan and walls expand and contract at different rates depending on temp and humidity. You need something stretchy like silicone for any transition in surface, even inside corners of the same kind of surface.


corylol t1_j2b42na wrote

Absolutely should NOT be grouted. Never grout a change of plane like this.


ShewTheMighty t1_j2affjf wrote

As others have said:

1.) Remove old caulking. razor blade and peel should do the trick.

2.) Clean the area with a blue non scratch scotch bright pad and some shower cleaner to remove any remaining caulk. (Soap and water is probably best careful of cleaner with alcohol as it will get trapped and reduce the bond of the caulk. Be sure to let the area dry before caulking no matter what you use.)

3.) Apply backer rod; also called rope caulk, or filler rope, in gap, be sure to use appropriate size backer rod for wet areas, typically silicon. Snug but not packed in. You want it to be receded a consistent distance. (For deep areas you can stuff a smaller piece of rod farther back then stick the main single piece in front of that.)

4.) Apply painters tape above and below the gap ~1/4" from area you'll be caulking. I'd suggest using 1" tape because you'll likely be using quite a bit of caulking, especially if this is the first time for you, to cover that area and when you smooth it out you wanna be sure the tape is wide enough to catch excess.

5.) Apply silicone bathroom caulking, I like 'Alex Flex" but if it's cold where you are be sure to verify the caulk will set within the temperature, especially If there is cold outside are coming out via the crack. They make more expensive caulk for colder settings.

6.) smooth out with silicone caulk applicator. You can use your finger but with large gaps you'll have better luck with an applicator.

7.) Remove painter's tape prior to drying. sometimes you can run over the caulk again with the applicator to smooth out the transition from where tape was removed.

8.) Let dry for 24 hours prior to use, lightly touch to make sure the caulk is firm and you're good to go. (12 hours maybe enough dry time but with such a large gap and winter upon us, more time is recommended.)

Hope that helps, good luck.


akmacmac t1_j2bmxt1 wrote

This is a great post, but Alex Flex is not the right stuff for this application. Alex Flex is a siliconized acrylic latex meant for painting projects. It’s not supposed to be in wet areas. The only thing I’m aware of that should be used here is 100% silicone.


ShewTheMighty t1_j2cmgs9 wrote

Fair point. The 100% silicone is the best option. Honestly never paid attention to the fact it was a mix. Alex Flex is commonly available, "100% waterproof" (when not submerged), and often cheaper though.

Since the area in question is above the tubs water line it would do the job fine but you are right, 100% silicone is better so long as you don't want/need to paint the area.


8Julio8 t1_j2bqddk wrote

Some Siliconized acrylic latex is rated for wet areas. Any tub and shower caulk that’s not 100% silicone will probably be siliconized acrylic latex.


akmacmac t1_j2brnzw wrote

That’s true, and they’re definitely easier to work with, but Alex Flex is definitely not the right thing to use here. If not pure silicone, should definitely be using something that states for use in tubs and showers for this application.


climbtigerfrog OP t1_j2bo1r4 wrote

Thanks for the detailed advice!


ShewTheMighty t1_j2clzhi wrote

Happy to help.

As one of the replies to my post said Alex Flex may not be the "best" option compared to a 100% silicon caulking alternative. That said Alex Flex is marketed as 100% water proof, so long as it is not submerged. In my experience it would work fine in this application since it's above the tubs water line but 100% silicone is better.

Edit: I'd probably go with something like GE's "supreme silicone kitchen and bath" for a 100% silicone option. It's readily available.


DickeyDooEd t1_j293gw6 wrote

Wow, big gap, I wonder why it was done like that. I suggest the backer rod then fill the shower full of water with the drain covered to weigh it down. Then use 100% neutral curing silicone. If it's just white GE makes one that is guaranteed to not mold. I have used it and it's very good. I believe it's call Supreme. Just make sure you us a Neutral curing silicone. You can get it color matched through Mapei, Laticrete etc.

Most big box stores will carry it. Do not use caulk or Siliconized caulk. On all change of planes you must use 100% silicone. Caulk is just gonna crack. Use a smoothing tool to put the silicone in and a spray bottle with water and a couple of drops of Dawn. It will give you professional results. Once put on give it a long time to cure as that is one huge gap. Then drain the water and you should be good to go.


DeathMonkey6969 t1_j2b6wrz wrote

> I wonder why it was done like that.

To me it looks like the pan has settled.


climbtigerfrog OP t1_j2boab0 wrote

Thanks! I think the gap is there because the installer wanted to make the shower floor sloped for drainage. The existing caulk is my first attempt at sealing it.


med561 t1_j2axdd6 wrote


Scrape/clean out all the old silicone / mold

Clear area with 90% isopropyl to kill mold/moisture. Let that dry/breath for 24h

As other have said, buy some bathroom/tile backing rod and jam it in there this will give an anchor point for the next step, the gap here looks about the widest end of a tile spacer so someone likely put a bunch at the bottom for some reason, and leveled the tiles from there, maybe an uneven tub or floor idk.

Once dry, fill your bathtub with water to weigh it down

Fill the remaining _\ gap with Microban Silicone. Microban or similar generic bathroom specific silicone not regular silicone.

This will prevent mold buildup, regular silicone will be black within 3y

Let silicone dry 72H yes it is a pain in the ass to not use the shower for 72 Hours. You can get away with 48 but if possible give it a full 3 days to cure. Plastic line your shower and run a fan if you must.

Buy more silicone than you think, it won't go very far and depending on how well you do it you might need to do a little touch up.

For a nice seam there is a tool to round it or a bit of canola oil on the finger and smooth the silicone out manually leaving a good amount as it will shrink and pull inwards

Good luck.


climbtigerfrog OP t1_j2boq82 wrote

Thanks! I appreciate the drying time tip especially. I'm sure i didn't wait long enough last time.


sparcasm t1_j29sr30 wrote

You can clean it out and fill it flush with sanded grout.

After the grout is dry go over it with clear silicone.

Chose a grout that is much lighter than the rest of the grout as the silicone will darken the grout you applied in the crack.

It’s not a perfect solution but it does work.


AcornWoodpecker t1_j28ygyg wrote

Maybe put some weather strip in first then caulk over? I'd probably look into plumbers putty as another option that can take caulk over it.


Shmeepsheep t1_j2b301f wrote

Plumbers putty will dry up and crack away of used to fill that gap, won't provide a water tight surface, and would take a lot to fill that. Backer rod would be the appropriate backing for silicone, not caulk


AcornWoodpecker t1_j2cf7ms wrote

Yeah, backer rod is what I was thinking. It's basically the same thing as the weather strip tubes, different sections of the store for sure.

I guess I grew up using caulk as a general term for anything that covered a joint, be it silicon or traditional stuff. OP should choose their goop for their situation.


nashant t1_j29gui7 wrote

Are you sure the tray hasn't dropped? Looks to me like there was sealer there but it's degraded and split as the tray dropped.


DPearl42 t1_j2b6s8m wrote

Don’t use the polyseamseal! It gets very hard and brittle. Silicone is the best bet.


ScottyDontKnow t1_j2b8yu6 wrote

Fill the tub with water before you caulk as well. The weight of the water can cause the tub to slightly lower.


theonePappabox t1_j2bcwq5 wrote

Black caulk fills the biggest gaps. (That’s what I have been told.) I have only ever seen white caulk.


Vmax-Mike t1_j2bq6je wrote

You will have to do it in stages. I have a corner shower that I redid. On the big gaps, put a base bead in, then leave it alone to dry. That’s how I did mine. Obviously take that old caulking out, clean it, then start over.


jayg2112 t1_j2a26co wrote

I had a similar issue - I used pvc 1/2" round and then caulked it with marine grade caulk (more like epoxy iirc). It's been good for over 10 years now & still looks good to boot.


Barnettmetal t1_j2bmdvw wrote

Bathroom grade white silicone will be absolutely good you just need to apply it properly.


wastedkarma t1_j2c18tw wrote

And for the love of god if this this is a tub and not just a shower pan, FILL THE TUB WITH WATER before you caulk. You need to weight the tub down before the caulk is applied so it’s applied when the tub is maximally displaced.


drnoonee t1_j2dls8o wrote

I've used silicone meant for pools and the back of a spoon to smooth the seam. This has held for several years.


Nasty113 t1_j2epaai wrote

I’m really NOT liking what I’m seeing here. I have extreme doubts that the water has not penetrated the surface and is now behind the wall. Eventually an entire wall of tile is going to end up coming loose. I would put the likelihood of this at 90%. It won’t happen tomorrow or the next day but eventually it will.

If this is your home I would get it taken care when funds allow. I would recommend not showering in there for a few days and even put a small box tan or whatever pointing at that joint just to get some airflow going to make sure it’s to reduce any moisture that has penetrated the surface. If it’s a rental, I’d recommend using the backer rod and a silicone caulk. It’s not ideal but at least it should stop it from getting exponentially worse.

I really hate saying this because I’m not bragging but just to give a background. I’ve owned a flooring company for 34 years specializing in all sorts of tile, remodels, etc. We have done everything from residential homes, schools, hospitals, to military bases, etc.


Raul_McCai t1_j2b9ih8 wrote

I should think you could get a butyl (gasket material) seal that will fill the void and then use silicone to lock that in place and seal it all up


Jbrels24 t1_j2bv12i wrote

Why not grout it ?


jabowman t1_j2d74ak wrote

Quarter round


sparkseid t1_j2bbibh wrote

Scrape out the caulking and use grout , seal the grout.


hautwings t1_j2bjano wrote

Isn’t that a bad idea? The grout can crack from tub movement


newaccount721 t1_j2cy698 wrote

Yeah whoever flipped my house just grout in places like this. It all cracked within the first year. Pretty annoying I must say


Reelplayer t1_j28ws66 wrote

This shouldn't be filled. A gap at the bottom of the wall prevents water from climbing up behind the wall by capillary action.


Bubbagumpredditor t1_j290fkl wrote

It also allows your shower to leak water into the wall


Reelplayer t1_j291kgz wrote

Not if your wall is properly waterproofed. Red guard on the wall with a seal to the floor membrane, then tile or surround with a gap at the bottom. Standard stuff.


Talbotus t1_j28x6v8 wrote

As long as its waterproofed behind there this is correct. Makes it tougher to clean tho.


Reelplayer t1_j291vxj wrote

I would argue that old, nasty caulk under there is more difficult to clean. And mold behind the surround or water damaged drywall is much more difficult to deal with.


circle22woman t1_j291h43 wrote

A gap at the bottom won't stop water from working its way up since capillary action will "pull" the water up. And the gaps will get super gross unless it's constantly cleaned.


Reelplayer t1_j29270d wrote

That's not true. The gap allows a pressure break so the water can just spill right back into the pan.


circle22woman t1_j2c0ukn wrote

That's not how capillary action works. There is no "pressure" with capillary action.


Reelplayer t1_j2cag04 wrote

Yes that's true. Technically it's surface tension. I figured it would just be simpler for others to understand if I said pressure break. And it doesn't change the point of having a gap.