Issues recaulking bathtub

Over the weekend I set out to recaulk my bathtub, as the old caulk job was very messy and black with mildew. I scraped off the old stuff with a razorblade, washed the area with bleach and water, gave it a few hours to dry, and applied the new caulk. Allowed about 36 hours for the new caulk application to dry.
The tub surround does not appear to sit flush against my wall... there is up to a 1cm gap between the tub surround and wall, and when something presses on the tub surround there is obvious strain on the caulk, such that the seal has been broken in many sections.
Is there a way to avoid this problem? Does the tub surround need to be glued to the wall somehow prior to caulking? Or could there have been an issue with the way I applied the caulk that resulted in the seal easily breaking?
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This is just a guess, but I would be thinking that I need to get something up in behind the tub surround in the space between the tub surround and the wall. That should keep the tub surround from pressing in toward the wall and stop that movement which is causing the separation you mentioned.
I would probably try one of two things.
One is to use the same silicone caulk but first apply it to the joint and then use a flat taping tool and PRESS the caulk IN and UP to get it up behind the tub surround. Then, after that is done re-caulk the joint as you did before.
Or, maybe I would try using bathroom ADHESIVE CAULK first. That is the adhesive caulk that is used to set soap dishes in place etc. Do the same routine -- apply it and press it up in behind the tub surround. Then, use regular caulk and caulk the seam.
Again, just a guess, but that's what I would try.

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Same here
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snipped-for-privacy@gmail.com wrote:

sure the tub and surround do not move. Then caulk. Do you have a molding around the outside perimeter of the surround? If so, I would seriously consider taking it down to see how the surround is mounted. Hard to solve a problem with so much unknown - if the surround was slapped up to cover a damaged wall, you may have more to do than to fasten it.
When you want to caulk a fine seam around bathtub, it must be immaculately clean and dry - all soap scum, moisture, etc. Wipe with full-strength bleach, let dry, wipe with denatured alcohol, let dry, apply caulk. If you aren't steady with a caulking gun, use painter's tape for guide and remove it as soon as the caulk is in place and smoothed out. Silicone caulk, not latex.
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******* You might try filling your tub with water next time, before you caulk. I found out that the weight of the water can pull the tub down, causing it to break away from the newly applied caulk...same thing happens when you stand in the tub and use the shower.
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