Mold-Resistant Caulk for Acrylic Tub/Shower?

[Nate B.]

I have an acrylic tub and surround. For the seam between the top of the tub and the bottom of the surround, my contractor used caulking that didn't adhere so I had to remove it (assuming 100% silicone). I contacted American Standard (the manufacturer) and they recommended Loctite Tub & Tile Adhesive Caulk PolySeamSeal. This stuff adhered really well but grows mold daily. I've tried drying it off after each shower and tried putting car wax on it to help seal it which hasn't helped much. Any advice on a good mold-proof caulk that will adhere to acrylic tub/surround or something I could use to better seal the existing loctite caulk would be greatly appreciated. I have thought about trying to put 100% silicone caulk over the existing. I'd rather not remove the existing if possible.

There was a lot of flex between the tub and the surround before I put this new stuff on it, so the caulking/adhesive needs to help hold it together rather than just seal the joint. Thanks!

 

[Jadnashua]

Depending on the size of the gap, you may be able to use some foam caulk backer rod, then caulk over that. When you just put caulk in the gap, you have a relatively square chunk and when things move, it doesn’t stretch, and is more likely to just pull off of one side or the other. If you use the foam backer rod, then caulk, it forces the caulk into an hourglass shape, and the thinner cross-section can stretch, preventing it from pulling off of the edges unless there’s a huge amount of flex. To prevent mold takes three components, and you can only control one of them (moisture can be controlled, but food requires regular cleaning (soap scum, body oils, etc.), and the mold spores will be there pretty much whatever you do. You need all three components for mold to grow. It’s harder to get a nice smooth bead with pure silicone, but it can be done. Some comes with stuff in it to help reduce mold. So, shaping it right so it can stretch, keeping it clean, and drying after use should give you a longer service life.

For silicone to stick, you need to get the surfaces really clean and then dry before application, then ensure you wait the prescribed time before getting it wet. Depending on the one you use, that could be overnight, or as much as a week. Many will skin over sooner, but pay attention to the instructions.

 

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[Nate B.]

Thanks, I really appreciate the reply! All good things to know and keep in mind. I like your foam caulk backer rod idea. However, the gap I'm dealing with is smaller than the small sized backer rod that I've seen. And even though the gap is small, there was a lot of movement with the original caulk (I don't think the contractor glued this part of the bath/surround down very well against the studs behind). After a posted this, I was able to get in touch with the manufacturer again and they recommended DAP Kwik seal Ultra this time. I'll probably give that a try and post an update. I'm just worried that I won't be able to get 100% silicone to stick and I'm too lazy to try it again.