Filling Bathtub - Tile Gap

I completely renovated one of my bathrooms over 2 years ago...new tub, ceramic wall tile, etc. The gap between the top of the tub and the bottom edge of the 1st course of tile can't be more than 1/8". No matter what material I use to fill it, it eventually cracks, separates, and gets moldy looking. I've tried grout, standard latex caulk, anti-microbial caulk. I've tried to fill it in 2 segments... 1st fill the gap under the tile and behind the front edge, let cure, then do a "finish fill" of the front edge. That doesn't work either. A few months later, it looks like crap.
The old tub is actually much lighter than the original so there shouldn't be any settling. Besides, its been way too long. The only thing I haven't tried is rubbery silicone caulk.
Any ideas? Is silicone the answer??
THanks!
--Jeff
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I have read/seen on tv/whatever that when you do that caulking, you should first fill the tub with water so it's at it's heaviest.
nancy
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Typing error....
The NEW tub (fibergalss) is actually much lighter than the original (enamel over cast iron)...

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An old plumber once told me the best way to caulk a tub is when its full and you are naked inside of it. Eliminates the settling.
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I too have the same problem, I tried filling the tub and then running a bead of caulk, I even left the water in the tub for 24 hours. After I let the water out the tub would rise and push the caulk up. Then after a few months a bathing cycles the caulk pulls away and I am left with a huge bead of caulk hanging out. Nothing I have tried works.
Solution: replace caulk; take showers!
I wish I could make I could make it look good yet still function because the tub is a jaquzzi and its a shame to waste it..
SD
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on 8/10/2007 8:54 AM JB said the following:

Fiberglass tubs, and showers, should be installed on a bed of wet concrete or other material made for that purpose. That way, there is full support and no flexing of the bottom when stepped on or filled with water.
--

Bill
In Hamptonburgh, NY
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1. Caulk with tub full of water and you in it. 2. Use backer rod (foam) as the "foundation" for the caulk, if the gap is too broad or too deep.

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On a tiled surround and a sheet metal tub, I used some tiles that look like quarter rounds. I don't know the technical name. As I recall, the edges were beveled such that nibs along the tile edges were in contact with the wall and the top of the tub. There was then a gap to be filled with caulk against the wall and against the tub. I tend to use dark grout and caulking. This "quarter round" treatment is 25 years old and it still looks fine, never touched it. The look of it is reminiscent of the larger bullnose tile that were used over mortar years ago.
Bill

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Good idea! I hadn't thought of ceramic "shoe molding" around the edges.
--Jeff
wrote:

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There is a flexible seal you can buy that might solve your problem. It is a semi-rigid rubber, and it runs the legth of the tub. In my new house, I have fiberglass tubs, which I have never had before. I am seeing some separation similar to what you describe, although my walls aren't tile, they are the fiberglass surrounds. Eventually they will all be replaced, but I am trying the flexible seal for now.
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