Bathtub Caulking - fill the gap!

Hi all:
I've got a problem with the area around my whirlpool bath and surround. Problem is, I've got a wide gap between the tub and surround, especially at the faucet end of the tub. The gap at its worst is approximately a half inch wide, too wide for caulking alone. When we bought the house, the water was coming into the kitchen pantry downstairs every time we took a shower due to a crappy caulking job. We did a temporary fix with that dreadful rubber tape business, but that stuff of course doesn't stick all that well and is no permanent solution.
I saw another post on this topic awhile back, and replies suggested a material called backer rod to fill the gap, then you caulk over. After a trip to the local Home Depot, and dealing with an orange aproned bloke who had never heard of the stuff, he asked his resident plumbing expert.
The plumbing expert first informed me that he had never encountered this problem with a tub that HE had installed, because he'd do it right the first time. In addition, he had never heard of such a thing as backer rod in his 21 years as a professional plumber. I resisted the urge to ask what an obviously skilled plumber with 21 years experience was doing working at Home Depot.
Sorry, my HD rant got in the way of my original problem. Anyhow, I found the darned backer rod myself (showed it to plumbing expert, who declared it weatherstripping and inappropriate for the task at hand), stuffed it in the gap as directed on the package and caulked over it. My husband and I did without showers for several days to let everything get good and dry.
So, now we're using the shower and bath again. The pantry is staying dry for the moment. But the darned caulking has started peeling off the backer rod, especially right under the faucet and in a couple of other spots where it gets more wet.
I'm sure just the backer rod itself is stuffed in tight enough to hold the water back for awhile, but we need a more permanent solution. To add insult to injury, the black backer rod covered with white cracking caulking looks awful too.
Help!
KD
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Indeed it is not normally used in plumbing but normally for insulation behind exterior caulk if a gap is large. Did you use silicone caulk? Silicone caulk might not adhere well to it. You might instead use a water resistent sheetrock filler. Waterproof would be better if you can find one. Use one that is strong (not the light stuff made of beads that can be painted in 10 minutes). Or visit a tile store and see what they recommend.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Backer rod is used to keep sealant from filling large voidss and to keep the sealant from sticking to the other surfaces. Sealant is to stick to two materials and stretch / compress along one plane.
TB
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Ok, so it would appear that I have used the wrong material. Maybe arrogant HD plumber guy was right, although he didn't offer any solutions. To the HD employees and fans out there, I sincerely apologize.
It would appear that the caulking is not going to stick to this stuff, and it is 3/4 the way around the tub. Obviously I need to remove the job I just did and do it right. So what's right?
While there is a slight gap along the long side of the tub, caulking will probably be sufficient to fill it (I hope). The head of the tub is all right, caulking will fix it no problem. The wide gap at the foot of the tub however, has a 1/2 inch gap, too wide for caulking. Something needs to be stuffed in there before I can caulk over it. Is water resistent sheetrock filler then answer? Is there something different I can do?
Thanks,
KD

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
KD,

I recently had to purchase a lot of the backer rod to seal the gaps around windows in our new house construction. I found ours at a little mom and pop hardware store in town. It was in the painting section.
When I needed a little bit more, I looked at the local Lowes and, like you experienced, they looked at me like I was from Mars. I eventually found it myself in the weatherstripping area.

The caulking really doesn't "need" to stick to the backer rod. It's mainly just there to fill the gap so the caulking can span the two surfaces you are caulking. You could theoretically fill the gap with just caulking, but it would take a long time to dry and the caulking would not have any "flex" ability.

The backer rod I found at Lowes was a light blue color which may not show through as bad. But, most of the backer rod was black. Can you push the backer rod a little farther into the gap so there is more caulking covering it?
Anthony
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.