I have a long time customer with a caulking problem around her acrylic bathtub. When the tub is full, she sees a fairly significant gap between the tub and the wall tile at the faucet end of the tub.
When I recaulked it a couple of months ago, I (250#) was in the tub and that seemed to do the job. A couple of weeks after that, however, she said that the gap was showing up again.
We’re scheduling another caulking session for later this week and I would appreciate some input on what to look for. I haven’t worked with many acrylic tubs and I’m wondering if there is something I may have overlooked – or if there is a recommended caulk for acrylic tubs.
She bought her condo three years ago and had it extensively remodeled before moving in. The remodel included a complete gut and rebuild of the bathroom – and the contractor had to do part of the work from the downstairs neighbor’s condo. I have a nagging suspicion that there may be some structural issues that are letting the tub move excessively when full of water and her. (She probably weighs 130# soaking wet. – lol)
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I think we need to see pics of her in the tub soaking wet to make a proper diagnosis.. :)
Try filling the tub full of water, then caulking it..
If you used any kind of silicone, it will fail. It simply does not stick to acrylic. I've successfully, once, peeled all the silicone off an acrylic tub in one piece, like a gasket. :P
We used Mono Ultra Kitchen and Bath, which adheres well. It's finicky and unpleasant to use, but it says right on the tube "Excellent adhesion to blah blah, acrylic, blah blah."
There are other products that will stick, but I haven't used them.
From your description, the tub is deforming from the internal pressure of water when full. The sidewalls of the tub are being pushed outwards, which in turn pulls the end(s) in toward the center. It's logical, too, that the faucet-end of the tub would be the one to show more inward movement, as the backrest end of a tub comprises a sloped wall that acts a bit like the web in a structural I- or H-beam. This sort of thing does not happen with steel or C-I tubs; only with cheap FG or acrylics. The better grade of FG units have structural reinforcement glassed into them.
The proper fix to this is to pull the tub, re-frame things to support the sidewalls, and re-install. Then caulk with the product shown below.
If pulling the tub is not an option, you might try this product anyway; if anything is going to hold and stretch enough to keep that gap sealed, this would be it. It's a rubber-based thermoplastic caulking called Mulco Flextra. I use this quite successfully on acrylics and other difficult surfaces. I have yet to find anything it doesn't adhere to perfectly.
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