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I recently did some patch work on my bathtub caulking. Just a little to give it a few more months before I redo the entire bathtub. My tub is floating and has a tub surround.

My wife usually removes the caulk during the day and she prefers that I do the actual caulking as I am better at getting a good bead size.

One of the steps she does to prepare the scene for me is full the bathtub all the way with water for what she says "so the caulk wont pull away". My personal problem comes from the tub water was not full and I did the patch work. My wife was against that and insisted that I fill the tub and start over. To make all parties happy I did just that.

What am I accomplishing by filling the tub with water? The weight from that does not reflect the weight that will be in the tub (estimation alert) 95% of the time. If filling the tub with water is beneficial why all the way?

Most of the instructions I ran into make no mention of filling the tub with water at all.

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    I don't see the point. Either a) You caulk with an empty bath, and the bath deflects a bit when you put water in occasionally, or b) you caulk with a full bath, and the bath deflects a bit when you take the water out.
    – AndyT
    Commented Nov 12, 2015 at 14:20
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    Why on earth does your wife usually remove the caulk during the day? Once it's applied why can't it be left there?
    – Myles
    Commented Nov 12, 2015 at 20:34
  • @Myles As a favour to me. I hate being there with an exacto knife scraping the residual off. She values showers and does whatever she can to accelerate the process
    – Matt
    Commented Nov 12, 2015 at 20:42
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    @Myles I believe what he means is that when he is doing work like this his wife will remove the caulk during the day so he can do the work in the evening. I don't think he means that his wife randomly removes the caulk and he ends up having to re-do the work.
    – Sherwin Flight
    Commented Nov 13, 2015 at 5:30
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    Are we in an episode of the twilight Zone hear ?
    – Alaska Man
    Commented Aug 18, 2018 at 6:13

4 Answers 4

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While caulk is fairly elastic, it handles better under compression than tension. By filling the tub all the way, you expand the gap quite a bit. Once the caulk is applied and the tub drained, the caulk compresses. During normal use, the caulk will likely never be in tension. As you'd have to add more weight than a tub full of water, before the caulk had to fill a gap larger than when it was applied.

Also, there's an old saying. "Happy wife, happy life" - Unknown

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    It's not so much the caulk itself but the interface between the caulk and the bath/wall. Compression tends close up cracks, tension tends to open them.
    – Peter Green
    Commented Nov 12, 2015 at 21:47
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Depends on the tub, to some extent, and how (or if) it was bedded when installed. Acrylic, fiberglass and thin steel tubs do noticeably deform with a load, especially if not bedded (I'm a fan of the good old plaster bed under the tub.)

Most cast-iron tubs don't deform to any noticeable extent.

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  • Are you saying that I should fill it all the way every time I re caulk then? I would think that I should not fill it that much as that is not the weight the tub will experience all the time.
    – Matt
    Commented Nov 12, 2015 at 14:16
  • One day I will redo the tub as the surround is about 3 inches ahead of the tubs edge. That is a problem for future Matt though.
    – Matt
    Commented Nov 12, 2015 at 14:17
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the water pulls the tub to the position it is in when you take a bath the sides slitly deflect and it pulls down from the surround so filling is the best practice to fill the voids and have a longer lasting seal that wont leak

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  • Are you saying that I should fill it all the way every time I re caulk then? I would think that I should not fill it that much as that is not the weight the tub will experience all the time.
    – Matt
    Commented Nov 12, 2015 at 14:16
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    I dont think it will be as bad on a re calk, but a first time I always fill er up
    – Ed Beal
    Commented Nov 12, 2015 at 14:26
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So, filling a bath with water before applying sealant (caulk), is going to make the job of applying it a whole lot more difficult depending on the size of your bath and where it is situated.

You either have to lean over the water at odd angles, or actually get in the bath with the water in it!

I can see absolutely no issue with applying the sealant and right after you are done, fill the bath with water.

For my bath, it is far easier and more comfortable to actually stand/kneel in the bath whilst applying sealant, particularly around the tap area, which is always the most difficult area.

Unless you are an exceptionally slow worker, the first sealant you will have applied, should only have been in place for 15 to 20 minutes at most, so it will still be wet!

So, do yourself a favour - fill the bath just after applying sealant.

You also need to consider how good your job of removing old sealant, any mould and grit etc. actually was - the smoother and cleaner the area of application, the better the job will be.

To me, that and using high quality sealant, is more important than filling the bath with water. You are far more likely to end up with gaps later on, if you don't do a decent job of removing the old sealant first.

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